No Common Candidate Genes for Resistance to Fusarium graminearum, F. proliferatum, F. sporotrichioides, and F. subglutanins in Soybean (Glycine max L.) Accessions from Maturity Groups 0 and I: Findings from Genome-Wide Association Mapping

Seedling diseases and root rot, caused by species of Fusarium, can limit soybean (Glycine max L.) production in the United States. Currently, there are few commercially available cultivars resistant to Fusarium. This study was conducted to assess the resistance of soybean maturity group (MG) accessions from 0 and I to Fusarium proliferatum, F. sporotrichioides, and F. subglutinans, as well as to identify common quantitative trait loci (QTL) for resistance to these pathogens, in addition to F. graminearum, using a genome-wide association study (GWAS). A total of 155, 91, and 48 accessions from the USDA soybean germplasm collection from maturity groups 0 and I were screened with a single isolate each of F. proliferatum, F. sporotrichioides, and F. subglutinans, respectively, using the inoculum layer inoculation method in the greenhouse. The disease severity was assessed 21 days post-inoculation and analyzed using non-parametric statistics to determine the relative treatment effects (RTE). Eleven and seven accessions showed significantly lower RTEs when inoculated with F. proliferatum and F. subglutinans, respectively, compared to the susceptible cultivar 'Williams 82'. One accession was significantly less susceptible to both F. proliferatum and F. subglutinans. The GWAS conducted with 41,985 single-nucleotide markers identified one QTL associated with resistance to both F. proliferatum and F. sporotrichioides, as well as another QTL for resistance to both F. subglutinans and F. graminearum. However, no common QTLs were identified for the four pathogens. The USDA accessions and QTLs identified in this study can be utilized to selectively breed resistance to multiple species of Fusarium.

First report of Candidatus Phytoplasma australasia (16SrII- subgroup D) associated with virescence of Chia (Salvia hispanica L.) from India

Chia (Salvia hispanica L., Lamiaceae) is an important commercial and medicinal crop recently popularized in India and widely cultivated in Karnataka (Joy et al., 2022). During the field survey of chia crop diseases, characteristic virescence like symptoms were observed at Main Agricultural Research Station, UAS, Raichur as well as at Mysuru and HD Kote region. The incidence was ranged from 2 - 4 per cent in an area of 30 hectares. Typical symptoms associated with chia are malformed shoot and/or inflorescence axis with reduced floral parts with greenish florets. The stem axis become thick, flattened, leaves are reduced towards terminal region. A total of five phytoplasma suspected samples and five suspected healthy samples were used for identification purpose. The Plant Genomic DNA Miniprep Kit (Sigma Aldrich, USA) was used to extract the DNA from five symptomatic and five asymptomatic samples and the DNA was used as template to amplify the phytoplasma-specific 16S rDNA gene using P1/P7 primers (Deng and Hiruki, 1991; Schneider et al., 1995) followed by nested PCR using R16F2n/R16R2 primers (Gundersen and Lee 1996). The expected 1.25-kb amplicon was detected from the suspected symptomatic samples. Nested PCR products were purified and sequenced from both the directions using ABIX370 Genetic Analyzer (Applied Biosystems, Waltham, MA). The analysis revealed that all five sequences shared 100 per cent identity with Candidatus Phytoplasma aurantifolia (OM649850, ON975012) and Tomato big bud phytoplasma (EF193359). The in-silico RFLP pattern of F2n/R2 primed region of 16S rDNA gene analyzed by using iPhyClassifier (Zhao et al. 2009) revealed that the sequence shared 98.72 per cent nucleotide sequence similarity with coefficient value of 1.00 to the reference strain RFLP pattern of 16Sr group II, subgroup D (witches'-broom disease of lime; U15442). Based on 16SrDNA sequences and in-silico RFLP analysis, the phytoplasma associated with the chia virescence was identified as a member of 16SrII-D group. Further, SecA gene was also amplified from the samples using SecAfor1/SecArev3 primer pair (Hodgetts et al., 2008). All samples produced ~400 bp products and sequenced as detailed above. Sequence analysis by nBLAST revealed 100 per cent similarity to Ca. P. australasia (MW020545) and Ca. P. aurantifolia isolate Idukki Kerala 1 (MK726369) both representing 16SrII-D group phytoplasma. The representative sequence (16Sr: PP359693, PP359694; secA:PP386558, PP386559) were deposited in GenBank. Chia virescence phytoplasma belonging to Ca. phytoplasma australasia has not been reported anywhere. The phytopathological studies associated with chia crop are very limited. Joy et al. (2022) reported the occurrence of foot rot disease caused by Athelia rolfsii. Several hosts are recorded to be associated with 16SrII D phytoplasma which includes china aster, eggplant and crotalaria (Mahadevakumar et al., 2017, Yadav et al., 2016a, b). Now the wide occurrence of the phytoplasma in the area might have transmitted by vectors. The occurrence of virescence is of great importance as it affects the overall yield which reduces the market value. To our knowledge, this is the first report of a group 16SrII-D phytoplasma associated with chia virescence in India.

First report of soybean root rot caused by Fusarium falciforme in the Republic of Korea

Phytopathogenic Fusarium species causing root and stem rot diseases in susceptible soybean (Glycine max (L.) Merrill) are a major threat to soybean production worldwide. Several Fusarium species have been reported to infect soybean plants in the Republic of Korea, including F. solani, F. oxysporum, F. fujikuroi, and F. graminearum (Cho et al., 2004; Choi et al., 2019; Kang et al., 2020). During the nationwide survey of soybean diseases in 2015, soybean plants showing symptoms of leaf chlorosis, wilting, and shoot death were found in soybean fields in Seosan, Chungnam. Fusarium isolates were obtained from the margins of sterilized necrotic symptomatic and asymptomatic regions of the stem tissues of diseased samples by culturing on potato dextrose agar (PDA). To examine the morphological characteristics, isolates were cultured on PDA at 25°C in the darkness for 10 days. Colonies produced white aerial mycelia with apricot pigments in the medium. Macroconidia were hyaline, slightly curved in shape with 3 or 4 septa, and their average length and width were 34.6± 0.56 μm (31.4 to 37.8 μm) and 4.7±0.16 μm (4.1 to 5.8 μm), respectively (n = 20). Microconidia were elongated, oval with 0 or 1 septum, and their average length and width were 11.4±0.87 and 5.2±0.32 μm, respectively (n = 20). The colonies and conidia exhibited morphological similarities to those of F. falciforme (Xu et al., 2022). Using the primers described by O'Donnell et al. (2008), identity of a representative strain '15-110' was further confirmed by sequencing portions of two genes, the translation elongation factor 1-alpha (EF-1α) and the second largest subunit of RNA polymerase II (RPB2). The two sequences (GenBank accession No. OQ992718 and OR060664) of 15-110 were 99% similar to those of two F. falciforme strains, 21BeanYC6-14 (GenBank accession nos. ON375419 and ON331931), and 21BeanYC6-16 (GenBank accession nos. ON697187 and ON331933). To test the pathogenicity, a single-spore isolate was cultured on carnation leaf agar (CLA) at 25℃ for 10 days. Pathogenicity test was performed by root-cutting assays using 14-day-old soybean seedlings of 'Daewon' and 'Taekwang'. Ten-day-old mycelia of 15-110 were collected from the CLA plates by scraping with distilled water, and the spore suspension was filtered and diluted to 1 × 106 conidia/mL. The roots of the soybean seedlings were partially cut and inoculated by soaking in the diluted spore suspension for two hours. The seedlings were then transplanted into 12 cm plastic pots (11 cm in height) and grown in a growth chamber at 25°C, 14h light/10h dark for 2 weeks. The infected plants exhibited wilting, observed brown discoloration on the root, and eventually died within 2 weeks, whereas the control plants inoculated with sterile water remained healthy. F. falciforme 15-110 was reisolated from infected plants, but not from the uninoculated controls. The morphology of the re-isolated fungus on PDA and its target gene sequences were identical to those of the original colony. To the best of our knowledge, this is the first report of root rot in soybean caused by F. falciforme in the Republic of Korea. Fusarium spp. induce a range of diseases in soybean plants, including root rot, damping-off, and wilt. Given the variable aggressiveness and susceptibility to fungicides among different Fusarium species, it is imperative to identify the Fusarium species posing a threat to soybean production. This understanding is crucial for developing a targeted and tailored disease management strategy to control Fusarium diseases.

Biological Control of Rapeseed Clubroot (Plasmodiophora brassicae) using the Endophytic Fungus Didymella macrostoma P2

Didymella macrostoma P2 was isolated from rapeseed (Brassica napus), and it is an endophyte of rapeseed and an antagonist of three rapeseed pathogens, Botrytis cinerea, Leptosphaeria biglobosa and Sclerotinia sclerotiorum. However, whether or not P2 has a suppressive effect on infection of rapeseed by the clubroot pathogen Plasmodiophora brassicae remains unknown. This study was conducted to detect production of antimicrobials by P2 and to determine efficacy of the antimicrobials and P2 pycnidiospores in suppression of rapeseed clubroot. Results showed that cultural filtrates (CF) of P2 in potato dextrose broth and the substances in pycnidiospore mucilages exuded from P2 pycnidia were inhibitory to P. brassicae. In the indoor experiment, seeds of the susceptible rapeseed cultivar Zhongshuang No.9 treated with P2 CF and the P2 spore suspension (P2 SS, 1 × 107 spores/ml) reduced clubroot severity by 31% to 70% on the 30-day-old seedlings compared to the control (seeds treated with water). P2 was re-isolated from the roots of the seedlings in the treatment of P2 SS, the average isolation frequency in the healthy roots (26%) was much higher than that (5%) in the diseased roots. In the field experiment, seeds of another susceptible rapeseed cultivar Huayouza 50 (HYZ50) treated with P2 CF, P2 CE (chloroform extract of P2 CF, 30 µg/ml) and P2 SS reduced clubroot severity by 29% to 48% on 60-day-old seedlings and by 28% to 59% on adult plants (220 days old) compared to the control treatment. The three P2 treatments on HYZ50 produced significantly (P < 0.05) higher seed yield than the control treatment on this rapeseed cultivar, and they even generated seed yield similar to that produced by the resistant rapeseed cultivar Shengguang 165R in one of the two seasons. These results suggest that D. macrostoma P2 is an effective biocontrol agent against rapeseed clubroot.

Identification of pathogen-specific novel sources of genetic resistance against ascochyta blight and their underlying genetic control

Global chickpea production is restricted by ascochyta blight caused by the necrotrophic fungi ascochyta rabiei. Developing locally adapted disease-resistant cultivars is an economically and environmentally sustainable approach to combat this disease. However, the lack of genetic variability in cultivated chickpeas and breeder-friendly markers poses a significant challenge to ascochyta blight-resistant breeding efforts in chickpeas. In this study, we screened the mini-core germplasm of Cicer reticulatum against a local pathotype of ascochyta rabiei. A modified mini-dome screening approach resulted in the identification of five accessions showing a high level of resistance. The mean disease score of resistant accessions ranged between 1.75±0.3 and 2.88±0.4 compared to susceptible accessions, where the mean disease score ranged between 3.59±0.62 and 8.86±0.14. Genome-wide association analysis revealed a strong association on chromosome 5, explaining ~58% of the phenotypic variance. The underlying region contained two candidate genes (Cr_14190.1_v2 and Cr_14189.1_v2), characterization of which showed the presence of a DNA binding domain (cl28899 & cd18793) in Cr_14190.1_v2 and its orthologs in C. arietinum, whereas Cr_14190.1_v2 carried an additional N-terminal domain (cl31759). qPCR expression analysis in resistant and susceptible accessions revealed ~3 and ~110-fold higher transcript abundance for Cr_14189.1 and Cr_14190.1, respectively.

Effect of fungicide and timing of application on management of Phoma black stem of cultivated sunflowers in the United States

Phoma black stem (PBS), caused by Phoma macdonaldii Boerema (teleomorph Leptosphaeria lindquistii Frezzi), is the most common stem disease of sunflower (Helianthus annuus L.) in the Northern Great Plains (NGP) region of the United States (US). However, the impact of PBS on sunflower yield in the US is unclear, and a near complete absence of information on the impact of fungicides on disease management exists. The objectives of this study were to determine the impact of PBS on sunflower yield, the efficacy of available fungicides, the optimal fungicide application timing, and the economic viability of fungicides as a management tool. Fungicide timing efficacy was evaluated by applying single and/or sequential applications of pyraclostrobin fungicide at three sunflower growth stages in ten field experiments between 2017 and 2019. Efficacy of ten fungicides from FRAC groups 3, 7, and 11 were evaluated in four field experiments between 2018 and 2019. The impact of treatments on PBS were evaluated by determination of incidence, severity, maximum lesion height (MLH), disease severity index (DSI) and harvested yield. Nine of the ten fungicides evaluated, and all fungicide timings that included an early bud application, resulted in disease reductions when compared to the non-treated controls. The DSI was negatively correlated to sunflower yield in high-yield environments (p=0.0004; R2 = 0.3425), but not in low- or moderate- yield environments. Although FRAC 7 fungicides were generally most efficacious, the sufficient efficacy and lower cost of FRAC 11 fungicides make them more economically viable in high-yielding environments at current market conditions.

Multiple forms of resistance to the Phomopsis stem canker pathogens Diaporthe helianthi and D. gulyae in sunflower

Phomopsis stem canker of cultivated sunflower (Helianthus annuus L.) can be caused by multiple necrotrophic fungi in the genus Diaporthe, with Diaporthe helianthi and D. gulyae being the most common causal agents in the United States. Infection begins at the leaf margins and proceeds primarily through the vasculature, progressing from the leaf through the petiole to the stem resulting in formation of brown stem lesions centered around the petiole. Sunflower resistance to Phomopsis stem canker is quantitative and genetically complex. Due to the intricate disease process, resistance is possible at different stages of infection and multiple forms of defense may contribute to the overall level of quantitative resistance. In this study, sunflower lines exhibiting field resistance to Phomopsis stem canker were evaluated for stem and leaf resistance to multiple isolates of both D. helianthi and D. gulyae in greenhouse experiments and responses to the two species were compared. Additionally, selected resistant and susceptible lines were evaluated for petiole transmission resistance to D. helianthi. Lines with distinct forms of resistance were identified and results indicated that responses to stem inoculation were strongly correlated (Spearman's coefficient 0.598, P < 0.001) for the two fungal species while leaf responses were not (Spearman's coefficient 0.396, P = 0.076). These results provide a basis for genetic dissection of distinct forms of sunflower resistance to Phomopsis stem canker and will facilitate combining different forms of resistance to potentially achieve durable control of this disease in sunflower hybrids.

Picarbutrazox effectiveness added to a seed treatment mixture for management of Oomycetes that impact soybean in Ohio

None of the current oomycota fungicides are effective towards all species of Phytophthora, Phytopythium, Globisporangium, and Pythium that affect soybean seed and seedlings in Ohio. Picarbutrazox is a new oomyceticide with a novel mode of action towards Oomycete pathogens. Our objectives were to evaluate picarbutrazox to determine i) baseline sensitivity (EC50) to 189 isolates of 29 species, ii) the efficacy with a base seed treatment with three cultivars with different levels of resistance in 14 field environments; and iii) if the rhizosphere microbiome was affected by the addition of the seed treatment on a moderately susceptible cultivar. The mycelial growth of all isolates was inhibited beginning at 0.001µg and the EC50 ranged from 0.0013 to 0.0483 µg a.i. ml-1. The effect of seed treatment was significantly different for plant population and yield in 8 of 14 and 6 of 12 environments, respectively. The addition of picarbutrazox at 1 and 2.5 g a.i. 100 kg seed-1 to the base seed treatment compared to the base alone was associated with higher plant populations and yield in 3 and 1 environment, respectively. There was limited impact of the seed treatment mefenoxam 7.5 g a.i. plus picarbutrazox 1 g a.i. per 100 kg seed-1 on the oomycetes detected in the rhizosphere of soybean seedlings collected at the V1 growth stage. Picarbutrazox has efficacy towards a wider range of oomycetes that cause disease on soybean and this will be another oomyceticide tool to combat early season damping-off in areas where environmental conditions highly favor disease development.

Wheat rhizosphere-derived bacteria protect soybean from soilborne diseases

Soybean [Glycine max (L.) Merr.] is an important oilseed crop with a high economic value. However, three damaging soybean diseases, soybean cyst nematode (SCN; Heterodera glycines Ichinohe), Sclerotinia stem rot caused by the fungus Sclerotinia sclerotiorum (Lid.) de Bary, and soybean root rot caused by Fusarium spp., are major constraints to soybean production in the Great Plains. Current disease management options, including resistant or tolerant varieties, fungicides, nematicides, and agricultural practices (crop rotation and tillage), have limited efficacy for these pathogens or have adverse effects on the ecosystem. Microbes with antagonistic activity are a promising option to control soybean diseases with the advantage of being environmentally friendly and sustainable. In this study, 61 bacterial strains isolated from wheat rhizospheres were used to examine their antagonistic abilities against three soybean pathogens. Six bacterial strains significantly inhibited the growth of Fusarium graminearum in the dual-culture assay. These bacterial strains were identified as Chryseobacterium ginsengisoli, C. indologenes, Pseudomonas poae, two Pseudomonas spp., and Delftia acidovorans by 16S rRNA gene sequencing. Moreover, C. ginsengisoli, C. indologenes, and P. poae significantly increased the mortality of SCN second-stage juveniles (J2) and two Pseudomonas spp. inhibited the growth of S. sclerotiorum in vitro. Further growth chamber tests found that C. ginsengisoli and C. indologenes reduced soybean Fusarium root rot disease. C. ginsengisoli and P. poae dramatically decreased SCN egg number on SCN susceptible soybean "Williams 82". Two Pseudomonas spp. protected soybean plants from leaf damage and collapse after being infected by S. sclerotiorum. These bacteria exhibit versatile antagonistic potential. This work lays the foundation for further research on the field control of soybean pathogens.

First report of Xanthomonas campestris pv. campestris causing black rot on oilseed rape (Brassica napus L.) in France

In October 2022, v-shaped necrotic lesions were observed on the leaf margins of field-grown winter oilseed rape (WOSR), Brassica napus L., in western France (Ille-et-Vilaine (35) and Maine-et-Loire (49) departments). Disease incidence on volunteers and cultivated WOSR was generally low (5-10 %) but occasionally up to 80% on some fields. Leaf sections sampled from the margin of necrotic leaf tissue were dilacerated in sterile deionized water and the extract was spread onto tryptone soya agar (TSA) with cycloheximide (100 mg.L-1) and Polyflor (Syngenta, France) (2ml.L-1, containing 5 mg.L-1 propiconazole) then incubated at 28°C for 2 days. Colonies were yellow-pigmented, mucoid, and convex, which are morphological characteristics of Xanthomonas spp. colonies. The partial fyuA and gyrB gene sequences were amplified for eight isolated strains (CFBP 9155, CFBP 9156, CFBP 9157, CFBP 9158, CFBP 9159, CFBP 9161, CFBP 9162, and CFBP 9163) using primers of Fargier et al. (2011), and sequenced (Genoscreen, France). The sequences were deposited under numbers OR232891 to OR232898 for fyuA and OR634932 to OR634939 for gyrB. BLASTN analysis of the sequenced fyuA amplicon showed 100% identity and query coverage with the fyuA fragment of Xanthomonas campestris pv. campestris (Xcc) CFBP 6865R (Bellenot et al., 2022). BLASTN analysis of the sequenced gyrB amplicon showed two allelic forms: one showed 100% identity and query coverage with the gyrB fragment of Xcc strain CFBP 6865R (Bellenot et al., 2022), the other one showed 100% identity and query coverage with the type strain Xcc CFBP 5241 (ATCC33913) (Vorhölter et al., 2003). Moreover, two qPCR tools were used to identify the strains successfully as Xcc (Köhl et al., 2011; Rezki et al., 2016) which target the same gene encoding a hypothetical protein and whose primers overlap. The pathogenicity of the eight isolated strains was validated using a bacterial suspension (108 CFU.ml-1) for i) leaf spraying until runoff onto the leaf surfaces of WOSR plants previously maintained at saturated humidity for 48 hours, ii) wound-leaf inoculation of the two youngest true leaves with scissors that had been dipped into the bacterial suspension. Both tests were performed on 3-week-old WOSR plants of the Aviso (INRAE) genotype. Deionized water was used as negative control. Strains CFBP 5241 and the strain CFBP 4954 (Fargier et al., 2007) were used as positive controls for disease expression. Tested plants (seven for spray inoculation and four for wound-leaf inoculation per strain and control condition) were incubated in a greenhouse at 20°C/24°C (night/day). Isolated strains and the strain CFBP 4954 caused yellow lesions with both inoculation methods that necrotized starting about 10 days post inoculation (dpi). The spots coalesced within 14 dpi to form necrotic areas. The type strain CFBP 5241 caused mild symptoms, with only yellow lesions that did not coalesce. Plants inoculated with water remained symptomless. To complete Koch's postulate, re-isolations were achieved. Re-isolated strains on TSA showed the same colony morphology as described above. All re-isolated strains were identified as Xcc based on partial gyrB sequencing and Xcc specific qPCR test (Rezki et al., 2016). This first report in France and the recent identification in Serbia (Popović et al., 2013) may illustrate the emergence of the disease on this crop in Europe. The prevalence and consequences of this disease should be evaluated over a wider geographic area.

First Report of Leaf Spot Caused by Paramyrothecium foliicola on Peanut in China

Peanut (Arachis hypogaea) is an important economic and oil crop in China. In September 2022, leaf spots were observed on peanut in Luoyang city, Henan province, China (34°49'N, 112°37'E). The disease occurred on about 30% of the peanut leaves in only one 0.5-acre field. Symptoms appeared primarily as brown spots, that varied in shape, and appeared round, oval or irregular. In addition, some disease patches exhibited a concentric ring pattern. Small pieces (5×5 mm) of five diseased leaves were surface disinfected in 3% NaClO for 2 minutes, rinsed three times in sterile distilled water, dried on sterilized filter paper, and cultured on potato dextrose agar (PDA) at 25°C for 3 days. Five isolates with uniform characteristics were obtained and subcultured by transferring hyphal tips to fresh PDA. The colonies of the isolates were circular and the margins were clean. The colonies showed white coloration, and after 5-7 days of incubation on PDA plates, concentric rings with dark green sporodochia appeared on the surface of the colonies. The conidiophores branched repeatedly. The conidiophore stipes unbranched, hyaline, 10.0 to 23.2×1.5 to 3.3 μm (n=50). The conidia were rod-shaped or long oval and single-celled, measuring 4.6 to 8.6×1.4 to 3.1 μm (n=100). Based on these characteristics, the five isolates were identified as Paramyrothecium foliicola (Lombard et al 2016). Genomic DNA was extracted from the representative isolates LH-1-1 and LH-1-2. The internal transcribed spacer (ITS), RNA polymerase II second largest subunit (RPB2), calmodulin (CmdA), and translation elongation factor 1-alpha (tef1) loci were amplified and sequenced using the following primer pairs: ITS1/ITS4 (White et al. 1990), RPB2-5F2/RPB2-7cR (O'Donnell et al. 2007), CAL-228F/CAL-2Rd (Carbone & Kohn 1999), and EF1-728F/EF2 (O'Donnell et al. 1998), respectively. BLASTn analysis revealed that the sequences of ITS (OR352397.1 and OR417392.1), RPB2 (OR413573.1 and OR420678.1), CmdA (OR413572.1 and OR420677.1), and tef1 (OR413574.1 and OR420679.1) had 99 to 100% (553/558 bp, 721/721 bp, 597/598 bp, and 384/389 bp) similarity to P. foliicola (MN593634.1, MN398038.1, OM801785.1, MK335967.1). A phylogenetic tree based on the Maximum Likelihood method also confirmed that the two isolates converge on the same branch as P. foliicola. Pathogenicity tests were performed using leaves of 60-day-old peanut plants (cv. Zhonghua 8). Briefly, uninfected healthy leaves (non-wounded) were inoculated with 30-µl drops containing a spore suspension (5×105 conidia/ml) of LH-1-2, and peanut leaves inoculated with sterile distilled water served as controls. All treatments were incubated in an incubator at 25℃ and high relative humidity with a 12:12 hour light-dark cycle. After 5-7 days, inoculated leaves showed symptoms similar to those observed in the field, while no symptoms were observed on control leaves. The pathogenicity tests were repeated three times. The fungus was reisolated from the infected leaves and identified as P. foliicola based on morphological and molecular characteristics, thus fulfilling Koch's postulates. P. foliicola has previously been reported to cause leaf spot of tomato and mung bean, stem canker of cucumber (Huo et al. 2022; Sun et al.2020; Huo et al. 2021). To our knowledge, this is the first report of P. foliicola causing leaf spot on peanut in the world. Identification of this pathogen will be helpful in monitoring peanut diseases and developing disease control strategies.

Development and Validation of a Resistance Management Model for the Soybean Cyst Nematode, Heterodera glycines

Plant-parasitic nematodes are a key yield limiting pest of crops around the world. Deployment of plant resistance genes are an important management tactic for many economically important plant-parasitic nematodes. The selection for virulence in nematode populations is a major threat to the effectiveness of resistance gene-based management. Little research has gone into resistance management modelling despite the importance of both plant-parasitic nematodes and resistance genes for their management. In this paper we report on a cyst nematode resistance management model created to explore the factors which are most important for determining the durability of resistance genes to this important family of plant-parasitic nematodes. The relative dominance of virulence expression, the level of inbreeding, and the number of generations per cropping season were the most important factors in predicting resistance gene durability. Aspects of cyst nematode biology that reduce the number of generations per season for a portion of the population had a much smaller effect on the durability of resistance genes. These factors included delayed hatching within a season and early dormancy. The accuracy and utility of the model was tested using the soybean cyst nematode (SCN) rhg1-mediated resistance system. The model accurately predicted the rate at which virulence to the rhg1b resistance gene developed in Iowa over a two-decade period. The model suggested resistance gene pyramids as the most durable management solution for SCN with multiple possible avenues to obtain acceptable efficacy and durability.

First Report of Peanut Black Pod Rot Caused by Berkeleyomyces rouxiae in China

Peanut (Arachis hypogaea L.) is an important oilseed and cash crop cultivated in over 100 countries worldwide. The major producers are China, India and USA (Ding et al. 2022). In September 2022, peanut pods exhibiting black necrotic symptoms on the shell surface were observed in Puyang, Henan Province, China. These black spots often merged to form larger necrotic spots on the shell. Disease incidence was 100% in susceptible varieties. Symptomatic shell pieces were surface sterilized with 75% ethanol for 3 min, rinsed three times with sterile water, and then transferred onto PDA medium supplemented with 25 µg/ml chloramphenicol (Long et al. 2022). Isolation frequency of a fungus with similar-appearing colonies from symptomatic pods was 81.7%. A pure culture of a representative isolate, PYHB, was obtained through single-sporing and maintained on PDA plates at 25℃ in darkness. The colony initially appeared white but turned black within 2 days. The isolate produced dark brown, unicellular chlamydospores, which were arranged in club-shaped chains consisting of two to seven cells. The size of the unicellular chlamydospores varied from 3.34 to 15.27 µm (average:6.81, n = 100) in length and 8.30 to 15.51 µm (average:11.29, n = 100) in width. The endoconidia were hyaline and cylindrical, measuring 7.91-22.94 × 1.69-4.81 µm (average: 12.16 × 3.13, n = 100). Based on morphological characteristics, the isolate was tentatively identified as a Berkeleyomyces sp. (Nel et al. 2018; Long et al. 2022). The ITS region of r-DNA, the ribosomal large subunit (LSU), the minichromosome maintenance complex component 7 (MCM7), and the 60S ribosomal protein RPL10 (60S) genes were amplified using ITS1/ITS4, LR0R/LR5, rouxMCM7-F/rouxMCM7-R and roux60s-F/roux60s-R primers, respectively (White et al. 1990; Vilgalys and Hester 1990; Nakane and Usami 2020). The sequences were deposited in GenBank (ITS: OR053803; LSU: OR053818; MCM7: OR058549; 60S: OR060656). Through BLASTn analysis of the NCBI GenBank database, the generated ITS and LSU sequences showed 100% identity to Berkeleyomyces rouxiae (GenBank MF952418.1 and MF948662.1, respectively) and B. basicola (GenBank MT221585.1 and MH868639.1, respectively). Importantly, the MCM7 and 60S sequences were 100% identical to B. rouxiae (GenBank MF967114.1 and MF967077.1, respectively). Phylogenetic analysis combining ITS, LSU, MCM7, and 60S sequences showed that the isolate PYHB clustered with B. rouxiae. To evaluate pathogenicity, surface-sterilized healthy peanut pods (n = 90) were immersed in a 1×106 spore/ml conidial suspension obtained from isolate PYHB for 5 min and placed in Petri dishes containing moistened cotton at 25°C for 10 days. Pods (n = 90) inoculated with sterile water served as controls. Inoculated pods displayed black necrosis 10 days after inoculation (dai), whereas no symptoms were observed on the control pods at 21 dai. The reisolated pathogen was shown to be identical to the original inoculum through morphological and phylogenetic analysis. Black root rot is a fungal disease caused by Berkeleyomyces spp. (syn. Thielaviopsis spp.) and affects various crops and ornamentals, such as cotton, tobacco, carrot, holly, and pansy (Rahnama et al. 2022). The causal agents B. rouxiae and B. basicola have similar morphological characteristics but can be differentiated through molecular characterization (Nel et al. 2018). To our knowledge, this is the first report of black pod rot in peanut caused by B. rouxiae in China. The finding from this study will contribute to the development of monitoring and management strategies to combat this destructive disease in peanut cultivation.

First report of milkweed (Euphorbia geniculata) as an alternative host for Colletotrichum truncatum in soybean fields in India

Soybean (Glycine max, L.), a major oilseed crop of India faces anthracnose disease caused by Colletotrichum truncatum (Nataraj et al. 2021). Several weeds serve as alternative hosts for Colletotrichum spp. (Hartman et al. 1986). Around 24.67% of soybean fields in the study area were infested with Euphorbia geniculata (Kutariye et al. 2021). In September 2021, milkweed plants died in the field, showing irregular circular lesions with wavy margins on the stem, change in color of veins and veinlets from brown to black and leaves exhibiting a twisted appearance at ICAR-Indian Institute of Soybean Research, India. Later on plants completely died and acervuli of average size 284 µm were visualized under stereo microscopy. Twenty milkweed samples were collected, rinsed, and surface sterilized with NaOCl (1%). Fungus isolation was done from leaf and stem and transferred to sterilized Petri plates with Potato dextrose agar (PDA). The plates were incubated at 25 ± 2°C for 48 h with dark/light (10h/14h) cycle. The fungi produced circular, raised, black to light grey colonies. Sickle shaped aseptate conidia, measuring 23.14 µm length, 3.18 µm width and hyphal width 5.49 µm were confirmed using a compound microscope with 20X magnification. The fungus was purified via hyphal tip method and pure culture was maintained on PDA at (26 ± 2°C). Milkweed seedlings in clay pots were inoculated with a conidial suspension of the fungus (106 conidia/mL) prepared from ten days old culture using serial dilution technique. Soybean variety JS 95-60 was inoculated by atomizing 20 ml of the same suspension on each plant. The negative controls for both milkweed and soybean were inoculated with sterile distilled water. Veinal necrosis and acervuli formation were observed on both milkweed and soybean, but no signs or symptoms of disease were observed in the controls. The re-isolated fungus from both the diseased hosts resembled original culture as they produced black to light grey colonies, sickle shaped aseptate conidia and ITS sequence (OR124845) exhibiting 100% resemblance to C. truncatum isolate C-17 (MN736513), thus confirming Koch's postulates. The pathogen was classified as Colletotrichum spp. based on morphological and cultural characters and the pathogenicity test (Rajput et al. 2021). To confirm identity of the pathogen infecting milkweed, DNA was extracted from the reisolated fungus using the HiPurA Fungal DNA Purification Kit (HiMedia, India). The internal transcribed spacer (ITS) region, beta-tubulin (TUB2) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes were amplified (Kumar et al. 2021). The GAPDH gene was amplified under similar reaction conditions except for annealing temp 59°C. For species level identification, the ITS, TUB2 and GAPDH gene sequences were submitted to GenBank with accession numbers OR004468, OQ869780 and OQ869781, respectively. The BLAST analysis of TUB2 and GAPDH gene showed sequence homology of 100% and 98.43% respectively with C. truncatum culture-collection CBS:151.35 (GU228156, GU228254). The isolate was identified as C. truncatum on the basis of molecular analysis, corroborating the above morphological identification. This is the first report of C. truncatum infecting milkweed in India, indicating milkweed as an alternative host in soybean fields, potentially raising inoculum levels and carryover between crops.

Ocurrence of Colletotrichum truncatum Causing Foliar Spot on Sesame (Sesamum indicum) in Mexico

Sesame (Sesamum indicum L.) is an oilseed crop that present agronomic advantages and nutritional contributions in regions where water and soil fertility are limiting. In September 2020 and October 2022, anthracnose symptoms were observed on sesame fields in Mocorito (25°29'04"N;107°55'03"W) and Guasave (25°45'40"N;108°48'44"W), Sinaloa, Mexico. The disease incidence was estimated at up to 35 % (10 has) in five fields. Twenty samples were collected with symptoms on the leaves. On leaves, lesions were irregular and necrotic. Colletotrichum-like colonies were consistently isolated on PDA medium and five monoconidial isolates were obtained. One isolate was selected as a representative for morphological characterization, multilocus phylogenetic analysis, and pathogenicity tests. The isolate was deposited in the Culture Collection of Phytopathogenic Fungi of the Biotic Product Development Center at the National Polytechnic Institute under the accession number IPN 13.0101. On PDA, colonies were flat with an entire margin, initially white, then dark gray with black acervuli and setae. The growth rate was 9.3 mm/day. Conidia (n=100) on PDA were hyaloamerosporae, 17.5- 22.7 × 3.6-4.5 μm, smooth-walled, falcated and pointed at both ends, with granular content. Acervuli showed setae acicular (2-3 septate setae) tapered to the apex. The mycelial appressoria were brown, obclavate and irregular. Morphological features matched those of the Colletotrichum truncatum species complex (Damm et al. 2009). For molecular identification, total DNA was extracted, and the internal transcribed spacer (ITS) region (White et al. 1990), and partial sequences of actin (ACT), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes were amplified by PCR (Weir et al. 2012) and sequenced. The sequences were deposited in GenBank under accession nos. OQ214919 (ITS), OQ230773 (ACT), and OQ230774 (GAPDH). BLASTn searches in GenBank showed 100%, 100%, and 100% identity to MN842788 (ITS), MG198003 (ACT), and MF682518 (GAPDH) of C. truncatum, respectively. A phylogenetic tree based on the Maximum Likelihood method and Bayesian Inference including published ITS, ACT, and GAPDH sequence data for C. truncatum species complex was generated (Talhinhas and Baroncelli 2021). In the phylogenetic tree, the isolate IPN 13.0101 was placed in the same clade of C. truncatum. Pathogenicity of the isolate IPN 13.0101 was verified on 15 sesame seedlings leaves (Dormilon variety) (15-day-old) disinfected with sodium hypochlorite and sterile water. Each leave was inoculated with 200 µL of a conidial suspension (1 × 106 spores/mL). Five plants non inoculated served as controls. All plants were kept in a moist chamber for two days, and subsequently transferred to a shade house where the temperature ranged from 25 to 30°C. All inoculated leaves developed irregular and necrotic lesions ten days after inoculation, whereas no symptoms were observed on the control leaves. The fungus was consistently re-isolated from the diseased leaves, fulfilling Koch´s postulates. The experiment was conducted twice with similar results. Colletotrichum spp. has been previously reported (Farr and Rossman, 2023) to cause sesame anthracnose in Mexico (Alvarez, 1976), Thailand (Giatgong, 1980) and Cuba (Arnold, 1986), but this is the first report of C. truncatum causing sesame anthracnose in Mexico. This disease is a recurrent problem in sesame fields in Sinaloa, therefore further studies are required to understand its impact. References: Alvarez, M.G. 1976. Fitofilo 71: 1-169. Arnold, G.R.W. 1986. Lista de Hongos Fitopatogenos de Cuba. Editorial Cientifico-Tecnica, Havana, Cuba. 207 p. Damm, U., et al. 2009. Fungal Divers. 39:45-87. https://www.fungaldiversity.org/fdp/sfdp/FD39-3.PDF Farr, D. F., and Rossman, A. Y. 2023. Fungal Databases, Syst. Mycol. Microbiol. Lab., Online publication. ARS, USDA. Retrieved February 05, 2023. Giatgong, P. 1980. Host Index of Plant Diseases in Thailand (2nd Ed) Dep. Agric, Min Agric Coop, Bangkok. Talhinhas, P., and Baroncelli, R. 2021. Stud. Mycol. 110:109. https://doi.org/10.1007/s13225-021-00491-9 Weir, B. S., et al. 2012. Stud. Mycol. 73:115. https://doi.org/10.3114/sim0011 White, T. J., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego.

Alternaria alternata Causing Brown Spot Disease on Walnut in Xinjiang, China

Walnut is one of the Xinjiang's characteristic dried fruits and the main source of income for farmers in walnut growing areas. In September 2019, Juglans regia leaves with brown spots were observed in a 10 hm2 orchard in Hotan area, the diseased leaf rate reached more than 25%. The leaf lesions were suborbicular to irregular, black-brown, 3 to 8 mm in diameter, with distinct dark borders. Colonies were isolated from 10 diseased leaves collected from two trees in the orchard. Leaf sections (4 × 4 mm) from diseased leaves were surface disinfested with 75% ethyl alcohol for 30 s and 2% NaClO for 3 min, washed with sterile water three times and then plated on potato dextrose agar (PDA) and incubated at 27℃ with a 12h/12h light/dark photoperiod for 4 days. A total of 7 fungal isolates were obtained by single-spore isolation. All the colonies were dark olivaceous on the PDA plates, with loose, cottony mycelium. On potato carrot agar (PCA), all fungal isolates produced conidial chains with numerous secondary chains. The conidia were ellipsoid or obpyriform with 0-3 longitudinal septa and 2-4 transverse septa, measuring 20.6 to 35.8 × 6.8 to 11.2 μm (25.5 ± 0.4 × 8.7 ± 0.2 μm, n=50). The morphological characteristics of the seven fungal isolates were consistent with the A. alternata descriptions of Simmons (2007). DNA was extracted from 50 mg of mycelia for the representative isolate HLP17-7. The internal transcribed spacer (ITS) region was PCR amplified using the universal primers ITS1 / ITS4 (White et al.1990), the partial coding sequence of endopolygalacturonase (endoPG) and the partial region of the histone 3 (H3) were amplified using primers PG2b / PG3 (Andrew et al. 2009) and H3-1a / H3-1b (Glass and Donaldson 1995) respectively. The products were sequenced and deposited in GenBank database under the accession numbers MW514319 [ITS], ON806938 endoPG, MW489301 [H3]. ITS, endoPG and H3 sequences had 99.81% (1/535 nt difference), 99.78% (1/448 nt difference) and 100% (0/417 nt difference) homology with homologous sequences of A. alternata strains (KP124306 [ITS], KP124006 [endoPG], MK085979 [H3]), respectively. During the early autumn, pathogenicity tests were carried out on the healthy mature leaves of seven-year-old Juglans regia plants in the field. Thirty leaves (five leaves per plant) were wounded with a sterile needle and then sprayed with a spore suspension prepared from 10-day-old PDA culture. Five wounded leaves per plant were sprayed with sterile water as control. All the treated leaves were covered with clear plastic bags for 3 days, and the experiment was replicated three times. On the 8th day after inoculation, brown spots appeared on the inoculated leaves, but no spots were observed in the control. Morphological observation and gene sequencing confirmed that the original fungal pathogen was re-isolated from the inoculated leaves. No colony was isolated from the control leaves. The pathogen causing the brown spot was identified as A. alternata based on morphological features and sequence analysis. A. alternata has been reported previously in Sichuan (Yang et al., 2017) causing brown spot in walnut. Xinjiang is dry with little rain and abundant sunshine, so there are few diseases on walnuts. However, the occurrence of brown spot disease has alarmed fruit farmers, walnuts are still at the risk of A. alternata infections even in dry environment with little rain. To our knowledge, this is the first report of A. alternata causing brown spot in walnut in Xinjiang, China. References: Andrew, M., et al. 2009. Mycologia. 101:95 Glass, M. L., and Donaldson, G. C. 1995. Appl. Environ. Microbiol. 61:1323. Simmons, E. G. 2007. Alternaria: An Identification Manual. CBS Fungal Biodiversity Centre, Utrecht, The Netherlands. White, T. J., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA. Yang, L., et al. 2017. Forest Research. 30(6):1004-1008.

First report of Colletotrichum cliviicola causing anthracnose disease of cowpea (Vigna unguiculata L. Walp) in Nigeria

Cowpea (Vigna unguiculata L. Walp) is a staple crop for millions of people in sub-Saharan Africa. However, its production is challenged by various abiotic and biotic constraints, including fungal diseases. In February 2020, around 10% of cowpea plants in IITA-Ibadan research plots (N7°29'49'' E3°53'49'') had symptoms of cowpea anthracnose disease (CAD). Symptoms included reddish brown spots, necrotic lesions, and vein streaks (Fig. 1). Diseased leaves were collected and taken to the laboratory, cut into small discs (3 mm in diameter) at advancing edges of lesions, and surface disinfected. Dry leaf discs were plated on PDA and incubated at 28°C for 5 days and sub-cultured in PDA for another 7 days. Isolates yielded phenotypes similar to Colletotrichum spp. (Fig. 2). DNA templates of four isolates (CC17 NG, CC19 NG, CC21 NG, and CC24 NG) were amplified using primers of the actin (ACT; ACT512F and ACT783R) (Carbone and Kohn, 1999) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH; GDF and GFR) (Templeton et al., 1992) genes and sequenced. The sequences were deposited in GenBank (accession numbers OP716557 to OP716560 for ACT and OP716561 to OP716564 for GADPH). BLASTn results on NCBI showed 98-100% identity of the four isolates with C. cliviicola. A bi-locus phylogenetic tree revealed that the isolates belong to the species C. cliviicola (Fig. 3) when compared with existing sequences in the GenBank (Table 1). To fulfill Koch's postulates, pathogenicity of each of the four C. cliviicola isolates was confirmed on 2-week-old cowpea plants cv. Ife Brown in screenhouse assays. Inocula were prepared from 7-d-old cultures washed with sterile water containing 0.1% TWEEN®20. Fungal suspensions were adjusted to 106 conidia/ml. Inoculations were carried out using the brush method. Leaves inoculated with sterile water containing 0.1% TWEEN®20 served as negative controls. Plants were kept in the screenhouse at room temperature for 21 days. All four C. cliviicola isolates produced CAD symptoms on inoculated leaves, while control leaves remained asymptomatic (Fig. 4). Each inoculated isolate was successfully re-isolated from symptomatic tissues and their identity confirmed. The fungus C. cliviicola is distributed in tropical and subtropical regions and has a wide host range, including several legumes (Damm et al. 2018). To our knowledge, this is the first report of C. cliviicola causing CAD in Nigeria and the world. There is the need to conduct a comprehensive distribution survey and develop appropriate control strategies in Nigeria. In addition, breeding for resistance to CAD in Nigeria should gear the efforts to all causal agents of the disease that occur across the country because historically CAD has been attributed to C. lindemuthianum and C. destructivum.

First Report of Collar Rot Caused by Sclerotinia sclerotiorum on Sesame (Sesamum indicum) in Mexico

Sesame (Sesamum indicum L.: Pedaliaceae) is the second most cultivated oilseed in Mexico with 80,000 ha per year. The seeds of this crop are used as a condiment, for the extraction of oil, and its medicinal properties. In October 2020, collar rot symptoms were observed in six sesame fields (SOPC-9539 TD variety) located in the Carrizo Valley (26°15'33.1"N; 109°01'37.9"W), El Fuerte, Sinaloa, México. Initially, small brown spots in the basal stem of the infected plants were observed. At advanced stages of the disease, the circumference of stem was necrotic with the presence of white mycelium that extends to the roots. Infected plants were showing symptoms of yellowing, wilting, and finally death. Disease incidence was estimated at 15%, counting the total of diseased plants in five counts done in arbitrary quadrants within the sesame fields. For fungal isolation, stem sections from the symptomatic basal stem were surface disinfected with 1.5% sodium hypochlorite for 2 min, then triple rinsed with sterile distilled water. The tissue sections were dried on sterile blotting paper and plated in Petri dishes with potato dextrose agar (PDA) culture medium. The plates were incubated at 28ºC in darkness for 48 h. Sclerotinia-like colonies were consistently isolated and four isolates from different locations were purified by the hyphal-tip method. Fungal colonies were formed of compact white mycelium, with the formation of sclerotia on the margin of the plate 6 days after inoculating PDA cultures. Sclerotia averaged 3.1 mm in diameter and 0.024 g. One isolate was deposited in the Culture Collection of Phytopathogenic Fungi of the Faculty of Agriculture of Fuerte Valley at the Sinaloa Autonomous University under Accession no. FAVF654. To confirm identification, genomic DNA was extracted from one isolate, and the internal transcribed spacer (ITS) region was amplified by PCR and sequenced directly using the primer pair ITS5/ITS4 (White et al. 1990). The resulting consensus sequence was deposited in GenBank under accession no. ON401416. BLASTn alignments in GenBank showed 100% identity of our sequence with the sequence of the type strain of Sclerotinia sclerotiorum ATCC 46762 (accession no. JX648201). Pathogenicity of the fungus was demonstrated by inoculating healthy sesame plants (Dormilón and SOPC-9539 TD ies), germinated in plastic pots with sterile substrate. Plants were inoculated with the FAVF654 isolate by applying 3 sclerotia at the base of each of the 12 plants. Twelve plants were left uninoculated, which served as controls. All the inoculated plants, of both varieties, developed the characteristic symptoms of the disease 7 days after inoculation, while the control plants remained symptomless. The pathogenicity test was performed twice with the same result. The fungus was reisolated from all the inoculated plants, thus fulfilling Koch's postulates. Sclerotinia sclerotiorum has been reported on sesame plants in Bulgaria and Korea (Farr and Rossman, 2022). To our knowledge, this is the first report of Sclerotinia sclerotiorum causing collar rot in sesame plants in Mexico and the Americas. This disease considerably reduces the yield of sesame; therefore it is necessary to develop effective disease-management strategies.

First Report of Leaf Spot Disease Caused by Boeremia linicola on Trifolium repens in China

Trifolium repens L. (White clover) a multipurpose legume crop, primarily utilized as a green manure in China. In March 2018, field investigations showed that a leaf spot disease occurred on T. repens in three fields with 50% to 80% incidence (50 plants in each field were investigated) in Nanchong City, Sichuan Province of China. Infected leaves showed symptoms of irregular dark brown spots in the center of leaves or at the leaf margins. Symptomatic leaves were surface sterilized with 3% NaClO for 3 min followed by 75% ethanol for 30 s and then rinsed in sterile water three times. Thereafter, tissue samples from margins of individual lesions were placed on potato dextrose agar and incubated at 25°C in the dark. Four pure cultures (Y3-1; Y3-2; Y3-3; Y3-4) were obtained by single spore isolation. On oatmeal agar medium, a colony reached 57 mm diameter after 9 d in alternating light and dark at 25℃. Fimbriate aerial hypha were flat and compact with pale brown to dark brown color. Conidiogenous cells were hyaline, smooth, ampulliform to doliiform (n = 30), ranging from 4.1 to 10.5 μm long (6.6 ± 1.8 µm) × 2.2 to 5.7 μm wide (4.1 ± 0.8 µm). Conidia were ellipsoidal to cylindrical, hyaline, thin walled, smooth, aseptate, with 2 to 4 polar guttules (n = 50), ranging from 3.2 to 11.3 μm long (6.3 ± 1.1 µm) × 2.1 to 4.1 μm wide (2.8 ± 0.4 µm). Conidial matrix was whitish. Morphologically these isolates resembled species in Boeremia (Chen et al. 2015). Genomic DNA of each culture was extracted from mycelia using the quick and safe method (Chi et al. 2009). The 28S large subunit of nuclear ribosomal RNA (LSU) region, internal transcribed spacer (ITS) region, RNA polymerase II second largest subunit (RPB2), translation elongation factor 1-α (TEF 1-α), β-Tubulin (TUB2) were amplified with corresponding primers (Carbone and Kohn 1999; Liu et al. 1999; Rehner and Samuels 1994; Sung et al. 2007; Vilgalys and Hester 1990; White et al. 1990; Woudenberg et al.2009). Sequences were deposited in GenBank with accession numbers: ON705759 to ON705766, ON734043 to ON734046 and ON841585 to ON841592. Phylogenetic analysis was conducted with combined sequences of the five loci using the maximum likelihood (ML) and the maximum parsimony (MP) methods. The four isolates and the extype strain of B. linicola (CBS 116.76) clustered together with high bootstrap support (BS) values (MLBS = 100; MPBS = 98). All sequences showed 100% identity to those of CBS 116.76, except the ITS region of our isolates (ON705759 to ON705762), which show 99.6% identity to that of CBS 116.76. Based on morphological characteristics and phylogenetic results, our isolates were identified as B. linicola, although the morphological characteristics of CBS 116.76 had not been characterized. To assess pathogenicity, a conidial suspension (approximately 105 CFU/mL) of isolate Y3-1 was sprayed on 1-month-old healthy plants in a greenhouse at 22℃ to 28℃. Plants sprayed with sterilized water were used as negative controls. The test was conducted three times, each with 3 plants. After 10 days, the leaves of the plants showed irregular brown lesions that were similar to the symptoms observed in the field, control plants remained healthy. The pathogen was reisolated and confirmed to be B. linicola, thus completing the verification of Koch's Postulates. Compared to B. exigua, a causal pathogen associated with leaf spot on white clover reported by Wang et al (Wang et al. 2021), B. linicola produced larger conidia, and the two species did not cluster together in the phylogenetic tree. To our knowledge, this is the first report of leaf spot disease caused by B. linicola on Trifolium repens in China.

First report of Rhizoctonia solani AG 4 causing brown bean of lima bean in Delaware

Lima bean production has been an economically valuable staple in Delaware agriculture for almost a century, with annual revenue approaching 8 million dollars (USDA-NASS, 2019; Evans et al. 2007). From 2019-2021, lima beans displaying symptoms of brown discoloration, referred to as "brown bean" were observed in the green baby lima variety 'Cypress' across multiple commercial and research fields. Symptoms were present in approximately 1-5% of beans and not visible until pods were opened for harvest. Thirty-seven symptomatic beans were collected and surface disinfested in 0.85% sodium hypochlorite for 30 s, rinsed in sterile deionized water for 30 s, sectioned into four pieces and plated onto potato dextrose agar (PDA) amended with 50 µg/ml penicillin G and streptomycin sulfate. Petri dishes were incubated at 23ºC and observed for colony morphology. Pure cultures were obtained with tan colonies that had mycelia with right angle branching and septations near the branch, consistent with the description of Rhizoctonia solani Kuhn (Sneh et al. 1991). DNA extraction and pathogen identification was confirmed by sequencing of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA using primers ITS4/ITS5 (White et al. 1990) for thirty-seven isolates collected in 2019 and 2020. Isolates were identified as Rhizoctonia solani AG 4 (99.9% sequence identity with GenBank Accession [MN106359.1].) A representative isolate was selected to complete Koch's postulates and the sequence was deposited in GenBank as accession number MW560551. To observe colonization ability, 10 detached pods were sterilized in 75% EtOH for 60 s, then rinsed in Milli-Q water. The detached pods were divided among two 150 mm Petri dishes containing a single 150 mm filter paper saturated with Milli-Q water. Five 1 mm2 agar plugs colonized with the representative R. solani isolate were placed 0.5 cm apart along the length of the pod. Plates were sealed with parafilm and left at room temperature. Control pods were kept in identical conditions but inoculated using clean agar plugs. The trial was repeated and a second trial was conducted on 12 attached asymptomatic pods from C-Elite Select lima bean plants at the succulent seed stage to complete Koch's Postulates. Pods were surface disinfested with 70% ethanol. Three attached pods were wounded with the tip of a sterile scalpel blade where a colonized agar plug was placed and loosely wrapped with a thin parafilm layer to maintain contact. Three attached pods not wounded were also inoculated with a colonized agar plug and wrapped by parafilm. Three wounded and non-wounded pods received clean agar plug controls. Both attached and detached pods were kept at room temperature for one week until symptoms began to manifest on the pod surfaces, at which point the beans from infected pods were removed and placed on PDA, three to a plate. In the attached assay, all beans of both wounded and non-wounded pods developed symptoms. The plates were stored in identical conditions and monitored for 5 days until tan colonies were observed. Culture morphology was consistent with the original isolate in all beans. Sequencing of the ITS region confirmed identity as R. solani AG-4. No symptoms were observed on control pods or seeds. Rhizoctonia solani is most frequently associated with symptoms of root rot (Sharma-Poudyal et al. 2015), but no stem symptoms are associated with the late season "brown bean" that has been observed throughout production in recent years. To our knowledge, this is the first report of Rhizoctonia solani AG 4 causing symptoms of brown bean of lima bean in Delaware. In preliminary observations, symptoms seem to be worse in pods that could have had contact with the soil directly or via rain splash. This disease cannot be detected until pods are split open, which has potential to reduce lima bean quality at harvest. Further monitoring should be conducted to quantify yield impacts and develop appropriate preventative and curative techniques.

First Report of Yeast-Spot Disease of Soybean Seeds Caused by Eremothecium coryli in Serbia

Over the last 15 years, the area planted with soybeans (Glycine max) in Serbia has increased drastically, from 131,000 hectares in 2005 to 230,000 in 2019, and the average yield reached 3.2 t/ha in 2020. The Province of Vojvodina is the most important soybean production region with 95% of the total soybean area in Serbia (www.stat.gov.rs). During the 2021 growing season, soybean seeds with various kinds of symptoms including colour changes, light and dark brown spots, blotching, necrosis, and shriveling were collected from soybean field before harvest of soybean cv. Dukat in the Tamiš locality (South Banat District, Vojvodina Province: GPS: 44°56'12.936"N 20°43'24.216"E) in Serbia. The incidence of symptomatic seeds was estimated at 6.4%. Symptomatic soybean seeds were surface disinfected with 2% NaOCl for 2 min, rinsed in sterile water, dried on sterile filter paper, placed on potato dextrose agar (PDA) and were incubated at 25°C in the dark for 10 to 14 days. The identification of fungi at the genus level based on morphological characteristics revealed the presence of species of Macrophomina, Botrytis, Cercospora and Alternaria, which were previously reported as pathogens of soybean seed in Serbia (Krsmanović et al. 2020). Also, seven white to slightly creamy colonies with yeast-like morphology were observed around seeds expressing discoloration and necrotic and sunken spots. Ten days later, microscopic observations of yeast-like colonies revealed the presence of globose budding cells (diameter of 20 to 28 μm) mostly single or rarely in short chains. Also, two to eight needle-shaped ascospores (52 to 80 μm in length) were arranged lengthwise in many cylindrical to naviculate asci (60 to 96 x 8 to 12, avg. 72.4 x 9.2 µm). Ascospores were with a unilateral, slender, flexuous, whip-like appendage. The morphology of the different fungal structures indicated that the pathogen was Eremothecium coryli (Pelgion) Kurtzman and it was further supported by molecular identification. Total DNA was extracted directly from fungal mycelium with a DNeasy Plant Mini Kit (Qiagen, Hilden, Germany) and PCR amplification performed with primers ITS1F (Gardes and Bruns 1993) and ITS4 (White et al. 1990). Sequence analysis of ITS region revealed that the Serbian isolate ND2/21 (GenBank Accession No. OL958602) shared the highest nucleotide identity of 100% with E. coryli isolate (Accession No. KY103387). For pathogenicity test, fresh soybean seeds (cv. Sava) were surface-disinfected with 2% NaOCl and rinsed in sterile water before inoculation. The seeds were pierced 3-4 times with a sterile insect pin through a drop of yeast suspension (concentration 106 ascospores/ml) of one selected single-spore isolate (ND2-21). Similarly, control seeds were pierced with sterile insect pins through a drop of sterile distilled water. Five inoculated seeds and control (five replicates per treatment) were arranged uniformly in a Petri dish (9 cm diameter) and incubated at 22 to 25°C in the dark and kept under >95% relative humidity during the first 48 h. Twenty days after inoculation, small brown necrotic lesions were visible on the soybean seeds. Re-isolation from symptomatic seeds on PDA dishes yielded yeast-like colonies with the same morphological characteristics as those used for inoculation, thus confirming Koch's postulates. The control seeds had no symptoms. This fungus is widely known as a pathogen of yeast spot disease on soybean seeds (Heinrichs et al. 1976; Kimura et al. 2008), but to our knowledge, it has never been reported in Serbia. Considering that invasive species Nezara viridula L. and Halyomorpha halys (STÅL, 1855), the vectors of this fungus, were reported in our country (Kereši et al. 2012; Šeat 2015) and that their mass appearance has been documented in recent years (Konjević et al. 2020), the presence of this pathogen has the potential to cause considerable damage and severe yield losses, resulting in significant economic impact on soybean production in Serbia.

First report of Athelia rolfsii (= Sclerotium rolfsii) causing southern blight on Pachyrhizus erosus in Mexico

Pachyrhizus erosus, commonly named jicama, is native to Mexico and is cultivated for its tuberous roots which are edible. In November 2021, field sampling was carried out in municipality of Huaquechula (18.748640N, 98.550817W, 1,580 m above sea level), state of Puebla, México. The disease had an incidence between 20 and 30% in approximately 10 ha. Infected plants showed wilting, yellowing foliage, rotting with white mycelium, abundant sclerotia were observed in the roots and tuber. Tuber splits transversely over time. Twenty plants with symptoms of disease were carried out to isolate the fungus. The sclerotia found in the tubers were disinfected with 3% NaOCl, rinsed twice with sterile distilled water, and excess moisture was removed and, transferred on Potato Dextrose Agar (PDA) culture medium and incubated at 28°C. Mycelial fragments from symptomatic tubers, were plated directly to PDA. Twenty representative isolates were obtained by hyphal-tip method, one for each diseased plant sampled (10 isolates from sclerotia and the other 10 from fragments of mycelium). After 10 days, colonies showed fast-growing, dense, cottony-white aerial mycelium, forming globoid to irregular sclerotia, measuring 1.0-1.7 mm in diameter (mean = 1.42 mm; n=100). The number of sclerotia produced per Petri dish ranged from 54 to 542 (mean = 274, n = 50). These sclerotia were initially white and gradually turned brown. Microscopic examination showed septate hyphae with some cells having clamp connections. Based on morphological characteristics, the fungal isolates were identified as Athelia rolfsii (Curzi) CC Tu & Kimbr (Syn: Sclerotium rolfsii Sacc) (Mordue 1974). For molecular identification, a representative isolate (Sr.1), the ITS region was amplified (650 bp) using primers ITS1/ITS4 (White et al. 1990). The obtained sequence (GenBank: ON206899) was subjected to BLAST analysis, where it had 100% identity with A. rolfsii isolates (GenBank: MG836252 and MH517363). Phylogenetic analysis with the neighbor-joining method in MEGAX, grouped the Sr.1 isolate into a common clade with different A. rolfsii isolates. Pathogenicity was confirmed by inoculating 20 tubers detached from healthy P. erosus variety "Criolla de Morelos", into which a portion of mycelium from the Sr.1 isolate was inserted with a sterile wooden stick at one point per tuber. In five tubers, only a sterile wooden stick was inserted as negative controls. The tubers were placed under laboratory conditions with relative humidity close to 100% and a temperature of 28°C. Symptoms like those observed in the field were observed after five days. Control tubers showed no symptoms. Additional pathogenicity tests were performed on 50 plants of 100-day-old P. erosus of the variety "Criolla de Morelos", grown in pots with sterile soil. Ten sclerotia of 10 days old were deposited at the base of the stem, 10 mm below the soil surface; as control treatment only, sterile distilled water was deposited on 20 plants. The plants were placed in a greenhouse (Center for Technological Innovation in Protected Agriculture of the Popular Autonomous University of the State of Puebla), at 28 ± 1°C and 90% of temperature and relative humidity, respectively. After 15 days, all inoculated plants showed symptoms similar to those observed in the field. Control plants showed no symptoms. A. rolfsii was re-isolated from inoculated tubers and stem, fulfilling Koch's postulates. Previously, A. rolfsii was reported in Mexico, causing southern blight on sesame (Hernández-Morales et al. 2018). To our knowledge, this is the first report of Athelia rolfsii causing southern blight on P. erosus in Mexico (Farr and Rossman 2022). This research is important to design management strategies and prevent its spread to other P. erosus-producing areas.

Fusarium pseudocircinatum causing stunting and malformation of sunflower plants in Brazil

Sunflower (Helianthus annuus L.) is among the main oleaginous crops used in Brazil. During January, 2017, at CCA/UFPB laboratory and greenhouses (Areia/Brazil, 6°58'12″ S; 35°42'15″ W), we observed various sunflower seeds (cultivar Olisun 3, 2017-2018 crop) highly infested with Fusarium. Those seeds were from crops in the municipality of Alagoinha -PB/Brazil (06º57'00'' S; 35º32'42'' W), supplied by Empresa Brasileira de Pesquisa Agropecuária/EMBRAPA. The emerged seedlings from these seeds were also contaminated, with 5% to 26% of them exhibiting stunting and malformation. Fusarium strains were isolated from symptomatic plants, and a single spore was used to grow pure colonies on potato-dextrose-agar (PDA) and synthetic-nutrient-poor-agar (SNA) media. Mycelia of PDA colonies were floccous and dense varying from yellow to orange. Fungal colonies developed aerial mycelium, producing orange pigments. On SNA, hyaline macroconidia, measuring 2.9-4.1 x 32.4-65.0 μm, slightly falcate with three to six septa. Oval microconidia, measuring 2.4-3.6 x 5.1-9.0 μm, were abundant in false heads forming on monophyalides. Chlamydospores were absent. Sterile hyphae were rarely formed. Colectively, the morphological features corresponded to species that belong to the Fusarium fujikuroi species complex (Leslie & Summerell, 2006). To assure the species identity, we sequenced the elongation factor 1α region of two representative isolates (i.e., F2 and F3, GenBank access numbers: MZ666934 and MZ666935, respectively) and compared them to the other Fusarium species found at Fusarium-ID and GenBank databases. Subsequently, we performed a maximum likelihood phylogenetic analysis including previously published sequences (Nicolli et al., 2020). Both isolates exhibited 100% similarity with Fusarium pseudocircinatum (MN386745), and clustered with its ex-type at 100% bootstrap values. The isolates were then grown on PDA amended with manitol to adjust the osmotic pressure to -1.0 Mpa, at 25 ± 2 ° C, for seven days (Sousa et al., 2008). A total of 100 disinfested sunflower seeds (cultivar Olisun 3, 2018-2019 crop) were distributed over the colonies and 48h later they were sown on sterile substrate maintained inside a greenhouse. About 30 days after inoculation, the emerged plants exhibited symptoms of stunting and malformation (60%) compared to controls, which were healthy. F. pseudocircinatum was reisolated from the symptomatic plants, completing Koch's postulates and identified based on above morphological and molecular biological methods. This test was performed twice. Fusarium pseudocircinatum is a broadly distributed and ecologicaly diverse species that infects several wild and cultivated plants. For instance, it was reported on seeds of the wild 'Peroba Rosa' (Aspidosperma polyneuron Muell. Arg.) in Brazil (Mazarotto et al. 2020). Infection of sunflowers may cause plant stand failures, thus resulting in yield and economic losses for Brazilian growers. The correct identification of any pathogen, especialy a generalist one such as F. pseudocircinatum, is crucial to develop eficient management strategies. To our best knowledge, this is the first report of F. pseudocircinatum causing stunting and malformation of sunflower plants in Brazil.

First report of Diaporthe ueckerae causing stem canker on soybean (Glycine max L.) in Colombia

In October 2018, soybean plants displaying elongated black to reddish-brown lesions on stems were observed in a field planted to the cv. BRS Serena in the locality of Puerto López (Meta, Colombia), with 20% incidence of diseased plants. Symptomatic stems were collected from five plants, and small pieces (∼5 mm2) were surface sterilized, plated on potato dextrose agar (PDA) and incubated for 2 weeks at 25°C in darkness. Three fungal isolates with similar morphology were obtained, i.e., by subculturing single hyphal tips, and their colonies on PDA were grayish-white, fluffy, with aerial mycelium, dark colored substrate mycelium, and produced circular black stroma. Pycnidia were globose, black, occurred as clusters, embedded in tissue, erumpent at maturity, with an elongated neck, and often had yellowish conidial cirrus extruding from the ostiole. Alpha conidia were observed for all isolates after 30 days growth on sterile soybean stem pieces (5 cm) on water agar, under 25ºC and 12 h light/12h darkness photoperiod. Alpha conidia (n = 50) measured 6.0 - 7.0 µm (6.4 ± 0.4 µm) × 2.0 - 3.0 µm (2.5± 0.4 µm), were aseptate, hyaline, smooth, ellipsoidal, often biguttulate, with subtruncate base. Beta conidia were not observed. Observed morphological characteristics of these isolates were similar to those reported in Diaporthe spp. by Udayanga et al. (2015). DNA from each fungal isolate was used to sequence the internal transcribed spacer region (ITS), and the translation elongation factor 1-α (TEF1) gene, using the primer pairs ITS5/ITS4 (White et al. 1990) and EF1-728F/EF1- 986R (Carbone & Kohn, 1999), respectively. Results from an NCBI-BLASTn, revealed that the ITS sequences of the three isolates (GenBank accessions MW566593 to MW566595) had 98% (581/584 bp) identity with D. miriciae strain BRIP 54736j (NR_147535.1), whereas the TEF1 sequences (GenBank accessions MW597410 to MW597412) had 97 to 100% (330-339/339 bp) identity with D. ueckerae strain FAU656 (KJ590747). The species Diaporthe miriciae R.G. Shivas, S.M. Thomps. & Y.P. Tan, and Diaporthe ueckerae Udayanga & Castl. are synonymous, with the latter taking the nomenclature priority (Gao et al. 2016). According to a multilocus phylogenetic analysis, by maximum likelihood, the three isolates clustered together in a clade with reference type strains of D. ueckerae (Udayanga et al. 2015). Soybean plants cv. BRS Serena (growth stages V3 to V4) were used to verify the pathogenicity of each isolate using a toothpick inoculation method (Mena et al. 2020). A single toothpick colonized by D. ueckerae was inserted directly into the stem of each plant (10 plants per isolate) approximately 1 cm below the first trifoliate node. Noncolonized sterile toothpicks, inserted in 10 soybean plants served as the non-inoculated control. Plants were arbitrarily distributed inside a glasshouse, and incubated at high relative humidity (>90% HR). After 15 days, inoculated plants showed elongated reddish-brown necrosis at the inoculated sites, that were similar to symptoms observed in the field. Non-inoculated control plants were asymptomatic. Fungal cultures recovered from symptomatic stems were morphologically identical to the original isolates. This is the first report of soybean stem canker caused by D. ueckerae in Colombia. Due to the economic importance of this disease elsewhere (Backman et al. 1985; Mena et al. 2020), further research on disease management strategies to mitigate potential crop losses is warranted.

First report of Soybean dwarf virus infecting white clover (Trifolium repens) in Finland

Soybean dwarf virus (SbDV, genus Luteovirus) is a single-stranded positive-sense RNA virus able to infect several legume species. SbDV was first reported in Japan where it was associated with significant yield losses in soybean (Tamada, 1969). Since then the virus has been detected worldwide. In Europe, the virus has only been reported from Germany (Abraham et al. 2007; Gaafar et al. 2020). In July 2018, several white clover plants (Trifolium repens L.) with leaf discoloration were observed in different locations in Oulu region in northern Finland. Individual plants were collected and analysed for the presence of viruses using small-RNA (sRNA) sequencing (Kreuze et. al. 2009) and reverse transcription-PCR (RT-PCR). Total RNA was extracted using EZNA micro RNA kit (Omega Bio-Tek, GA, USA). For sRNA analysis, sequencing libraries were constructed using the TruSeq small RNA library prep kit (Illumina, CA, USA) and sequenced on Illumina MiSeq platform. On average, 1.3 million single-end reads were obtained per sample, of which 27% were 18-25 nt long and used for the subsequent analysis. Contig assembly and virus identification with VirusDetect software (Zheng et al. 2017) detected SbDV in five out of six white clover samples analysed. Depending on the sample, 26-39 contigs (with lengths up to 301-469 nt) aligned to complete genome of a SbDV isolate previously described from white clover in USA (accession no. JN674402). The cumulative alignment coverage ranged from 35.5 % to 65.3 % with nucleotide identities between 94.4 % and 97.3 %. Additionally, two samples seemed to contain an unidentified closterovirus and one contained White clover cryptic virus 2. No additional viruses were detected from two of the samples.To confirm the presence of SbDV, the samples were tested by RT-PCR using primers MDF, MYF and MUR in multiplex (Schneider et al. 2011) together with SuperScript III One-Step RT-PCR System with the Platinum Taq DNA polymerase kit (Thermo Fisher Scientific, USA), essentially as instructed by the manufacturer. RT-PCR product of approximately 400 bp was produced from each of the five samples previously tested SbDV positive by sRNA analysis. No products were produced from the sample that was SbDV negative in sRNA analysis. Direct sequencing of two of the PCR products produced 347 and 361 bp sequences (GenBank: MZ355392 and MW929169) that were 95.7 % and 95.2 % identical, respectively, to a SbDV isolate (accession no. AB038148) that causes yellowing on soybean and is transmitted by Acyrthosiphon pisum (Terauchi et al. 2003). To our knowledge this is the first report of SbDV in Finland. SbDV is transmitted only by aphids (neither mechanical nor seed transmission occurs). In siRNA analysis all the isolates from Finland formed contigs that aligned almost perfectly (100 % coverage with ≥ 99 % nucleotide identity) to the coat protein (accession no. EF466131) of an SbDV isolate transmittable from white clover to faba bean by A. pisum (Abraham et al. 2007), an aphid common in Finland. Although significant yield losses by SbDV have only been reported on soybean (Tamada, 1969), the virus also causes symptoms in other legume crops, such as growth reduction on pea (Tian et al. 2017) and faba bean (Abraham et al. 2007), both of which are cultivated in Finland. References: Abraham et al. 2007. Plant Dis. 91: 1059. Gaafar et al. 2020. Front microbiol. 11: 583242. Kreuze et al. 2009. Virology 388:1. Schneider et al. 2011. Virology 412: 46. Tamada. 1969. Ann Phytopathol Soc Jpn. 35: 282. Terauchi et al. 2003. Phytopathology 93: 1560. Tian et al. 2017. Viruses 9: 155. Zheng et al. 2017. Virology 500: 130.

First Report of Leptosphaeria biglobosa 'brassicae' Causing Blackleg on Brassica juncea var. multisecta in China

Brassica juncea var. multisecta, a leafy mustard, is widely grown in China as a vegetable (Fahey 2016). In May 2018, blackleg symptoms, grayish lesions with black pycnidia, were found on stems and leaves of B. juncea var. multisecta during disease surveys in Wuhan, Hubei Province. Disease incidence was approximately 82% of plants in the surveyed fields (~1 ha in total). To determine the causal agent of the disease, twelve diseased petioles were surface-sterilized and then cultured on potato dextrose agar (PDA) at 20˚C for 5 days. Six fungal isolates (50%) were obtained. All showed fluffy white aerial mycelia on the colony surface and produced a yellow pigment in PDA. In addition, pink conidial ooze formed on top of pycnidia after 20 days of cultivation on a V8 juice agar. Pycnidia were black-brown and globose with average size of 145 × 138 μm and ranged between 78 to 240 × 71 to 220 μm, n = 50. The conidia were cylindrical, hyaline, and 5.0 × 2.1 μm (4 to 7.1 × 1.4 to 2.9 μm, n=100). These results indicated that the fungus was Leptosphaeria biglobosa rather than L. maculans, as only the former produces yellow pigment (Williams and Fitt 1999). For molecular confirmation of identify, genomic DNAs were extracted and tested through polymerase chain reaction (PCR) assay using the species-specific primers LbigF, LmacF, and LmacR (Liu et al. 2006), of which DNA samples of L. maculans isolate UK-1 (kindly provided by Dr. Yongju Huang of University of Hertfordshire) and L. biglobosa 'brassicae' isolate B2003 (Cai et al. 2014) served as controls. Moreover, the sequences coding for actin, β-tubulin, and the internal transcribed spacer (ITS) region of ribosomal DNA (Vincenot et al. 2008) of isolates HYJ-1, HYJ-2 and HYJ-3 were also cloned and sequenced. All six isolates only produced a 444-bp DNA fragment, the same as isolate B2003, indicating they belonged to L. biglobosa 'brassicae', as L. maculans generates a 331-bp DNA fragment. In addition, sequences of ITS (GenBank accession no. MN814012, MN814013, MN814014), actin (MN814292, MN814293, MN814294), and β-tubulin (MN814295, MN814296, MN814297) of isolates HYJ-1, HYJ-2 and HYJ-3 were 100% identical to the ITS (KC880981), actin (AY748949), and β-tubulin (AY748995) of L. biglobosa 'brassicae' strains in GenBank, respectively. To determine their pathogenicity, needle-wounded cotyledons (14 days) of B. juncea var. multisecta 'K618' were inoculated with a conidial suspension (1 × 107 conidia/ml, 10 μl per site) of two isolates HYJ-1 and HYJ-3, twelve seedlings per isolate (24 cotyledons), while the control group was only treated with sterile water. All seedlings were incubated in a growth chamber (20°C, 100% relative humidity under 12 h of light/12 h of dark) for 10 days. Seedlings inoculated with conidia showed necrotic lesions, whereas control group remained asymptomatic. Two fungal isolates showing the same culture morphology to the original isolates were re-isolated from the necrotic lesions. Therefore, L. biglobosa 'brassicae' was confirmed to be the causal agent of blackleg on B. juncea var. multisecta in China. L. biglobosa 'brassicae' has been reported on many Brassica crops in China, such as B. napus (Fitt et al. 2006), B. oleracea (Zhou et al. 2019), B. juncea var. multiceps (Zhou et al. 2019), B. juncea var. tumida (Deng et al. 2020). To our knowledge this is the first report of L. biglobosa 'brassicae' causing blackleg on B. juncea var. multisecta in China, and its occurrence might be a new threat to leafy mustard production of China.

First Report of Post-Harvest Tuber Rot of American Groundnut (Apios americana) Caused by Fusarium acuminatum

Apios americana Medik, commonly known as American groundnut, is a leguminous perennial vine crop native to North America and is cultivated in Japan and Korea (Chu et al. 2019). Its tubers are edible and believed to be very nutritious, especially for women just after childbirth. The tubers also contain secondary metabolites, saponin and genistein, which is good for human health (Ichige et al. 2013). However, the storage of tubers at inappropriate temperatures and humidity levels can cause severe fungal infection, and adversely affect tuber quality. During March and April 2020, a white to pale-orange fungal mycelia were observed on stored American groundnut tubers, with 10 to 15% of seed tubers rotten. Infected tubers were collected, and fungal isolates were isolated on potato dextrose agar (PDA) using the single spore isolation method (Leslie and Summerell 2006). A pure culture (isolate JC20003) was obtained and stored at the Bioenergy Crop Research Institute, NICS, Muan, Republic of Korea. The fungus was cultured on PDA and V8 liquid media for 7 days at 25℃ to observe its morphological characteristics. The length and width of macroconidia ranged from 20.6 to 52.9 μm and 2.9 to 5.1 μm, respectively (n = 30). The microconidia were 8.5 to 14.9 μm and 2.3 to 4.2 μm in length and width, respectively (n = 30). Macroconidia were broadly falcate, strongly septate, 2 to 6 septations with dorsiventral curvature; chlamydospores were formed in chains; and microconidia were fusiform with 0 to 1 septation observed. Genomic DNA of the isolate was extracted using Solgent DNA extraction kit (Solgent, Daejeon, Korea), followed by PCR analysis using the internal transcribed spacer (ITS5/ITS4) and elongation factor (EF-1/EF2) genes (White et al. 1990; O'Donnel 2000). PCR products were sequenced and analyzed to confirm species identity (Yang et al. 2018). These sequences were deposited in GenBank (accession numbers MT703859/ITS and MT731939/EF). BLASTn search analysis showed 100% sequence similarity with Fusarium acuminatum (isolates N-51-1/ITS and WXWH24/EF). Based on morphological and molecular data analysis, the fungus was identified as F. acuminatum (Leslie and Summerell 2006; Marin et al. 2012). Pathogenicity tests were conducted on five tubers inoculated with 5 mm mycelial plugs with three replicates, while a non-mycelial plug served as the control. After 5 days of incubation in plastic containers at 25 °C with high humidity, typical symptoms developed. No symptoms were observed on the control tubers; F. acuminatum was re-isolated from artificially inoculated tubers to complete Koch's postulates. This is the first report on post-harvest tuber rot caused by F. acuminatum in Apios americana.

First report of root rot and damping off disease in soybean (Glycine max) caused by Pythium deliense in India

Seedling rot symptoms were observed at Research Farm of ICAR-Indian Institute of Soybean Research, Indore, India. The infected seedlings had water-soaked lesions on the cotyledons and hypocotyls that gradually developed into brown lesions and further progressed to soft rot. These seedlings could be easily pulled-off from the soil. The diseased seedling samples were rinsed thoroughly in flowing tap water and eventually in double-distilled water and were subjected to surface sterilization with NaOCl(1%). The samples were further washed thrice with sterilized double distilled water. The root fragments were properly sterilized and placed on V8 juice agar as well as potato dextrose agar (PDA) media plates. These plates were incubated at 27± 2°C for 48 hours. After incubation, white fluffy mycelial growth was observed on both the media. The fungus was observed to produce brown round vesicles with mycelial attachment when observed under a compound microscope magnification of 20X. Subcultures of these fungal isolates were placed on PDA media and incubated for 7 days at (27±2°C). The pure fungal culture along with PDA media was cut into small pieces and mixed with a sterilized soil mix (70% soil and 20% sand and 10 % vermicompost) at the rate of one petri dish per pot (plastic pots of 10 cm depth) and covered properly with tin foil. These pots were subjected to substrate colonization for 10 days at room temperature and the substrates were shaken occasionally to improve infection efficiency of pathogen by enhacing inocula production. Seeds of soybean variety, Gaurav were sown in three replicates, each with 10 seeds in the inoculated pots. The control was established by sowing seeds in the soil mix, amended previously with plain PDA. The pots were maintained at 25 to 30 ºC with 45 to 50 % of soil moisture content under glasshouse conditions. In the inoculated pots, the fungus killed soybean seeds before and after germination. Some of the plants that emerged developed lesions were initially yellow and gradually turned to necrotic later. These lesions were found on the roots of the plant and at the base of the hypocotyl region. The soybean seeds planted in un-inoculated soil emerged but did not develop any necrotic lesions. When the causal organism was re-isolated from the diseased plant part it was found to be morphologically and culturally similar to theoriginal culture. The isolated pathogen was thus classified as Pythium deliense based on morphological and cultural characters as well as the pathogenicity test. (Plaats-Niterink 1981). For further confirmation of pathogen's identity, complete genomic DNA of the fungus was extracted using the HiPurA Fungal DNA Purification Kit (HiMedia, India). The nuclear rDNA region of the internal transcribed spacer and 5.8S rDNA was amplified by universal primers ITS 1 (5' TCCGTAGGTGAACCTGCGG 3') and ITS 4 (5' TCCTCCGCTTATTGATATGC 3') as mentioned by White et al. (1990). Amplification was performed in a 12.5 μL reaction volume containing 1.5 μL of 10X PCR buffer, 3 μL of 25 mM MgCl2, 1.2 μL of 2.5 mM deoxyribonucleotide triphosphates (dNTPs), 0.7 μL of 10 pM each primer (ITS 1 and ITS 4), and 1 μL of DNA template, 0.3 μL of 1 units of Taq DNA polymerase. The thermal cycle consisted of 4-minute initial denaturation at 94°C, followed by 35 cycles of 1-minute denaturation at 95°C, 30-second primer annealing at 57 The PCR products were sequenced and submitted to NCBI (GenBank Acc. MT2665888). The BLAST study of the fungal isolate showed 100% similarity with reference sequences of Pythium deliense (MT126658.1) in the GenBank. The isolate was identified as Pythium deliense on the basis of molecular analysis, corroborating the above morphological identification. Further, the beta-tubulin gene (Bt) was amplified with primers BtF (5'GCTGGCCTTGATGTTGTTCG3') and BtR (5'CGTGA AGAGTACCCAGAC CG3'). Similarly, the cytochrome oxidase gene was amplified with primers COXF (5'GGTGCTTTTTCAGGTGTAGTTGG3') and COXR (5'GCTCCTGCTAATACTGGTAATG T3'). The PCR products were sequenced and submitted to GenBank with accession numbers MW196444 and MW196445 respectively. In BLAST analysis, the beta-tubulin gene exhibited 100 percent sequence homology with Pythium deliense (MK752986.1) and cytochrome oxidase gene also showed 100 % sequence homology with Pythium deliense (HQ708566.1). Pythium deliense has been recorded worldwide causing disease in many agricultural crops including soybean but to our knowledge, this is the first study in India of the genus Pythium and Pythium deliense causing root rot and damping off of soybean.

First Report of White Rust Disease Caused by Albugo koreana on Camelina sativa in China

Camelina sativa, an herbaceous annual plant in the family Brassicaceae, is especially well known for its oilseed crop that produce camelina oil (Hovsepyan et al. 2008). In April 2016, white blister rust disease on C. sativa were observed in a cultivated farmland with an incidence of about 60% in Xinyuan County (43°33'39.17"N, 83°14'54.04"E), Xinjiang, China. Symptoms appeared as light-yellow chlorotic spots on the upper surface of the leaves and white blister on the corresponding lower surface. Blister sori were white, oval to ellipsoidal, scattered or coalesce, and 1.8 to 4 mm in diameter. Two representative voucher specimens were deposited in the Mycological Herbarium of Tarim University (HMUT 2527 and HMUT 2528), Aral, China. Sporangiophores hyaline, clavate or cylindrical, straight to slightly curved, (23.7 to) 27.9 to 37.9 (to 42.1) (av. 31) × (7.9 to) 9.6 to 13.7 (to 15.1) (av. 11.4) μm (n = 30), thick-walled on their lower parts, bearing sporangia in chains. Primary sporangia were globose to subglobose, wall equal thickness, and (9.5 to) 10.6 to 13.2 (to 14.3) (av. 11.9) μm in diameter (n = 50). Secondary sporangia were mostly subglobose to ovoid, with a subtruncated base, and (12.1 to) 13.2 to 16.9 (to 18) (av. 15.1) μm × (11 to) 12.1 to 15 (to 16.1) (av. 13.4) μm in size (n = 50). Oogonia were globose to subglobose, (39.7 to) 42.7 to 51.7 (to 54.1) (av. 48.3) μm in diameter (n = 30), irregular. Oospores were globose to subglobose, brown, (34.5 to) 37 to 42.7 (to 45.2) (av. 41.1) μm in diameter (n = 30), 3 to 5 μm wall in thickness, with single warts, 1.5 to 4 × 2 to 3.5 μm (n = 30). The morphological characteristics of specimens were consistent with those of Albugo koreana (Choi et al. 2007). To confirm the identification, genomic DNA were extracted directly from sori on diseased leaves from isolates HMUT 2527 and HMUT 2528, respectively. The internal transcribed spacer (ITS) rDNA and cytochrome oxidase II (cox2) mtDNA were amplified with primers DC6/LR-0 described by Choi et al. (2006) and cox2-F/cox2-R described by Hudspeth et al. (2000), respectively. A BLASTn search revealed that the ITS rDNA sequences (GenBank accession Nos. MW135444 and MW135445) were 99% (838/844 nucleotides)identical to that of A. koreana from Capsella bursa-pastoris (AY929829), and the cox2 sequences (GenBank accession Nos. MW147150 and MW147151) were 100% (567/567 nucleotides) identical to that of A. koreana from C. bursa-pastoris (AY927048). Based on the concatenated ITS and cox2 sequences, Maximum Likelihood and Bayesian analysis showed that pathogen from C. sativa with the reference isolate of A. koreana (ex C. bursa-pastoris) with high bootstrap support values and maximum posterior probability (100 ML BS and 1.00 BPP, respectively). For pathogenicity, sporangia collected from the infected leaves were suspended in sterile water at 4°C for 2 hours to improve zoospore release, and the zoospore suspension obtained from sporangial suspension (1×105 sporangia/ml) was inoculated to the lower surface of six healthy potted plants. Three non-inoculated plants were served as controls. Each plant was kept in a separate plastic humid chamber in a greenhouse with 25°C and 80% humidity for 15 days. Typical symptoms of white rust pustules developed on the inoculated plants were identical to that observed on the originally infected leaves. Control plants remained symptomless.. Based on morphological characteristics, molecular data, as well as pathogenicity tests, the pathogen on C. sativa was identified as Albugo koreana. A. koreana aslo is reported only on C. bursa-pastoris in Korea (Choi et al. 2007; Farr and Rossman 2020). To our knowledge, this is the first record of white rust disease caused by A. koreana on C. sativa, and the species is new to China. This report represents a new host plant association and a new geographical expansion for this species, presenting a potential threat to camelina production in northwest China.

Occurrence of Soybean Yellow Common Mosaic Virus in Soybean in China Showing Yellow Common Mosaic Disease

Soybean yellow common mosaic virus (SYCMV), a positive sense ssRNA virus classified in the genus Sobemovirus, was first reported and characterized in Korea (Nam et al., 2012). Currently, its only known host is soybean (Nam et al., 2012) on which it causes bright yellow mosaic and crinkling of the leaves (Lim et al., 2016). During a field survey in July 2019, bright yellow mosaic and mild crinkling symptoms were observed on soybean leaves (cv. Zhonghuang 13) in the Hubei province of China. To identify the possible pathogen(s) associated to the disease symptoms, leaves from five symptomatic plants were collected, pooled and total RNA was extracted using TRIzol® Reagent (Invitrogen, CA, USA). 10 μg of the total RNA was purified via magnetic beads (Thermo Fischer Scientific, USA) and a TruSeq RNA Sample Prep Kit (Illumina, San Diego, CA, USA) was then used to construct an RNA sequencing library. Transcriptome sequencing was performed on an Illumina HiSeq 4000 (LC Sciences, USA). The average insert size for the paired-end library was 300 ± 50 bp. After quality control, a total of 47.5 million clean reads were obtained and assembled using the Trinity software (version 2.8.5). The assembled contigs were searched against NCBI virus RefSeqs (ftp://ftp.ncbi.nlm.nih.gov/refseq/release/viral) by the BLASTx algorithm with a cutoff E value of ≤10-5. 12 contigs sized from 3,421 to 4,093 bp were found to share a sequence identity of 77.5%-94.1% with SYCMV isolates from Japan (LC332541) and South Korea (JF495127.1). No other virus matches were identified. The largest contig (4,093 bp, MT816507) covers 99% of the expected complete genome of SYCMV (4,121 bp, KX096577). To verify the accuracy of the sequence assembled, RT-PCR-Sanger sequencing was performed on a single field plant sample using primers designed for SYCMV (Forward, 5'-GAACAAAGAGTCTGGATCTT-3'; Reverse, 5'-TCCTTCCAAAACCTCGCGGG-3'). The sequence of the amplicon (3854 bp, MT997092) exhibited an identity of 99.9% to the HTS-derived SYCMV contig sequence. Phylogenetic analysis of the amplicon sequence revealed that the SYCMV isolate from China formed a distinct branch in the tree (Fig. S1). Sap from symptomatic field plants was used to mechanically inoculate two soybean cultivars (Jiunong 9 and Kefeng 1, 10 plants per cultivar), and leaves inoculated with phosphate buffer saline (PBS, 0.01 M, pH 7.5) served as a control (3 plants per cultivar). All but the control plants developed systemic bright yellow mosaic symptoms 10 days after inoculation (Fig. S2A). The infection of the soybean plants with SYCMV was confirmed by RT-PCR with the newly designed primers for SYCMV (Forward, 5'- CCTACAGGCATTGGTTTCGT-3'; Reverse, 5'-CGTGAGGTTCTTGCTTCACA-3', anticipated amplicon size: 2,210 bp) (Fig. S2B) and by amplicon sequencing (100% sequence identity with MT9979092). In addition, the infection was further confirmed by immuno-blotting using an antibody against SYCMV coat protein (synthesized by GenScript, USA) (Fig. S2C). Together, the results demonstrate that SYCMV is the causal agent of the bright yellow mosaic symptoms in soybean observed in the field. To the best of our knowledge, this is the first report of SYCMV on soybean in China. These findings shall not only alert local growers to a potential new threat to soybean production in their region, but also provide new insights on the transmission, epidemiology and pathological properties of SYCMV in China.

First Report on the Occurrence of an Aggressive Pathotype, 734, of Plasmopara halstedii Causing Sunflower Downy Mildew in Hungary

Downy mildew of sunflower (Helianthus annuus L.) is caused by Plasmopara halstedii (Farl.) Berl. et de Toni, leading to significant losses in crop production worldwide. The number of new and more aggressive pathotypes has increased rapidly over the last 10 years in Europe (Virányi et al. 2015, Bán et al. 2018), therefore, constantly monitoring the distribution of races is an important task. As part of regular surveys in June 2019, severe downy mildew was identified in some regions, appearing as chlorotic lesions along the veins of the adaxial side and white sporulation on the abaxial side of the leaves of severely stunted hybrids containing PI6 and PI7 resistance genes. The identification of the pathogen was performed microscopically based on morphological characteristics (average size of sporangia: 28x20 µm). Disease incidence (the ratio of diseased plants) ranged between 10 and 30% per field in three regions and resulted in moderate yield loss. Isolates (defined as a lesion per leaf) were collected from 4 to 8 infected leaves of each hybrid by region and stored at -70°C. Two, one and one isolates of P. halstedii were selected and characterized from the southeastern (Békés County), northern (Nógrád County) and northeastern (Borsod-Abaúj-Zemplén County) regions of Hungary, respectively. The pathotype of the four isolates was determined using the international standardized nomenclature method reviewed by Trojanová et al. (2017), including nine sunflower differential inbred lines (HA-304, RHA-265, RHA-274, PMI-3, PM-17, 803-1, HAR-4, QHP2 and HA-335). Zoosporangia from frozen sunflower leaves were washed off into bidistilled water and the concentration was adjusted to 3.5x104 sporangia/ml using a hemocytometer. Three-day-old seedlings with a radical of 1 to 1.5 cm long were immersed in the sporangial suspension and kept at 16°C overnight (Cohen and Sackston 1973). Inoculated seedlings were planted into trays containing clear moistened perlite (d = 4 mm) and grown in a growth chamber with a photoperiod of 12 h. The experiment was carried out twice with each isolate using 15 seeds/differential line with two replicates. Bidistilled water was sprayed on the plants 9 days after inoculation, and then trays were covered with a black polyethylene bag and maintained at 19°C overnight to induce sporulation. The first disease assessment was done based on cotyledons bearing white sporulation. Next, a second evaluation was performed 21 days after inoculation assessing stunting of the plants, chlorotic lesions on true leaves and damping-off. All 4 isolates examined caused disease on differential lines HA-304, RHA-265, RHA-274, PMI-3, PM-17 and HA-335, whereas the other lines showed no symptoms and signs of sunflower downy mildew. As a result, it was concluded that the presence of P. halstedii pathotype 734 was confirmed. This pathotype is likely widespread in Hungary as it could be detected from three different regions. Moreover, the possibility that pathotype 734 is present in Hungary has been raised before (Iwebor et al. 2018). This pathotype is already widespread in the USA and Russia and is considered to be highly aggressive, since it was able to infect hybrids with resistance genes PI6 and PI7 (Iwebor et al. 2018, Spring 2019). To our knowledge, this is the first report of pathotype 734 of P. halstedii in Hungary and Central Europe. Continuous monitoring and incorporation of new resistance genes into sunflower hybrids are essential steps in the future to control P. halstedii.

First Report of Colletotrichum brevisporum Causing Soybean Anthracnose in China

In March 2020, widespread anthracnose was observed on soybean (Glycine max) in southeastern Jiangsu (Nantong municipality; 120.53° E, 31.58° N) in China. Plants exhibited irregular brown necrotic lesions in stem and leaves, and pronounced wilting. The symptoms were detected in one soybean field, 0.42 ha, surrounded by healthy wheat fields. Approximately 65% of the soybean plants showed the disease symptoms, and crop yield was reduced by 28-35% with respect the yield achieved in previous years, when no symptoms were observed. The symptoms were consistent with those previously reported for anthracnose on soybean caused by Colletotrichum chlorophyti, C. cliviae and C. gloeosporioides (Barbieri et al. 2017; Mahmodi et al. 2013; Yang et al. 2012). Diseased, 3-week old plants were collected. Small pieces, approximately 1 cm2 in size, of symptomatic tissue were surface sterilized in 1.5% NaOCl for 1 min, and washed twice with sterile ddH2O. The pathogen was isolated and cultured on potato dextrose agar (Song et al. 2020), containing chloramphenicol (50 µg/mL), under darkness at 28 °C for 3 days. Sequence of internal transcribed spacer (ITS), actin (ACT), β-tubulin (TUB2) and glyceraldehyde 3-phosphate dehydrogenase (GAP/span>DH) genes was performed as reported by Yang et al. (2015). Sequences were submitted to GenBank under accession numbers MT361074 (ITS) and MT415548-MT415550 (ACT, TUB2 and GAPDH). Blast search revealed that the amplified sequences had 100% (ITS; C. brevisporum TCHD, MH883805), 97.66% (ACT; C. brevisporum S38, KY986905), 99.06% (TUB2; C. brevisporum PF-2, KY705061) and 100% (GAPDH; C. brevisporum LJTJ27, KP823797) matches to multiple C. brevisporum strains, whereas all reported C. chlorophyti, C. cliviae and C. gloeosporioides strains showed no similarity to at least 2 of the studied genes. Molecular phylogenetic tree constructed using MEGA7 confirmed the identity of the pathogen. ACT and ITS sequences were blasted separately in Muscle (https://www.ebi.ac.uk/Tools/msa/muscle/) and then combined together to make the phylogenetic tree. The evolutionary history was inferred by using the Maximum Likelihood method based on the Tamura 3-parameter model, and the tree with the highest log likelihood (-1749.2186) is shown in Figure 1. The Colletotrichum strains previously found causing anthracnoseon soybean, and other relevant strains used in taxonomic analyses were included in the phylogenetic tree. Microscope observations showed the presence of 15-µm-long cylindrical conidia and septate mycelium, and agree with those reported for the morphology of C. brevisporum by Damm et al. (2019). To confirm pathogenicity, the mycelia from a 2 day-old culture on PDA was collected and suspended in sterile ddH2O (≈ 106 cells/mL) to prepare the inoculum. The pathogen was sprayed-inoculated on stem and leaves of healthy soybean plants. In control plants, sterile ddH2O was used. Inoculated plants were maintained in growth chamber at 28 °C and 50% relative humidity. Typical anthracnose symptoms were obsered 20 days after inoculation (Figure 2). C. brevisporum was reported to produce anthracnose on pumpkin, papaya, mulberry, coffee, passion fruit and pepper in China (Liu et al. 2017; Liu et al. 2019; Xue et al. 2019). Here, we report for the first time C. brevisporum causing anthracnose on soybean, an economically-relevant crop in China.

Occurrence of Pratylenchus coffeae Causing Root Rot of Soybean in Shandong Province of China

Soybean (Glycine max L.) is a very important commercial crop in China (Li et al. 2019). Pratylenchus coffeae (Zimmermann, 1898) Filipjev & Schuurmans Stekhoven, 1941, is one of the most important root-lesion nematodes that invade the roots of many crops. In August 2018, five root and soil samples were collected in a soybean field, near Xipan village in Linshu county of Linyi City, Shandong Province, China (Fig. S1), to investigate the occurrence of root-lesion nematodes. The collected plants (cv. Lindou No.10) were growing poorly and the roots showed distinct brown lesions (Fig. S2). Pratylenchus spp. were extracted using the modified Baermann funnel method for 2 days (Hooper et al. 2005). On average, 395 root-lesion nematodes per kg of soil and 36 root-lesion nematodes per gram of fresh roots were extracted. The extracted root-lesion nematodes were disinfected with 0.3% streptomycin sulfate and cultured on carrot disks for propagation at 25°C. The species identification was based on morphological and molecular criteria. Key morphological features were determined for females and males. Measurements of females (n = 16) included body length = 561.0 μm ± 37.6 (standard deviation) (520.5 to 654.0 μm), tail length = 30.0 μm ± 1.9 (27.0 to 33.5 μm), stylet = 16.0 μm ± 0.6 (15.0 to 17.5 μm), a = 28.2 ± 2.3 (23.7 to 31.5), b = 6.4 ± 0.5 (5.7 to 7.3), c = 18.7 ± 1.8 (15.7 to 23.8), and V = 80.8% ± 2.1 (76.5 to 83.8%). Measurements of males (n = 16): body length = 511.0 μm ± 28.1 (range= 475.5 to 566.0 μm), tail length = 26.0 μm ± 1.3 (23.5 to 28.5 μm), stylet = 15.0 μm ± 0.5 (14.5 to 16.0 μm), spicule length = 17.0 μm ± 0.9 (16.0 to 18.5 μm), a = 30.8 ± 1.5 (28.0 to 33.2), b = 6.1 ±0.4 (5.6 to 6.9), and c = 19.8 ± 1.3 (18.1 to 22.2) (Fig. S3). All the morphological features of this population matched the description of P. coffeae (Castillo and Vovlas, 2007). DNA was extracted from an individual female as described previously (Wang et al. 2011). The rDNA-internal transcribed spacer (ITS) region and the D2/D3 region of the 28S rRNA gene were amplified by primers 18S/26S (Vrain et al. 1992) and D2A/D3B (De Ley et al. 1999), respectively. The PCR products were purified and sequenced. The obtained sequences of the ITS region (1,253 bp) and the D2/D3 region of 28S rRNA (781 bp) were deposited in GenBank. The ITS sequences of the root-lesion nematode obtained in this study (GenBank Accession no. MT879294) exhibited 99% identity with several P. coffeae sequences available in the GenBank (e.g., KR106219, MT586756, KY424205, and MN749379), and the obtained D2/D3 region sequence (MT879295) exhibited 100% identity with several P. coffeae sequences (e.g., MT586754, MN750755, MK829009, and MH730447). Both morphological and molecular data confirmed the presence of P. coffeae. To confirm reproduction on soybean, the obtained root-lesion nematode population was used in a greenhouse (25°C) assay to fulfill modified Koch's postulates. About 20 days after sowing, eight pots, each with one soybean plant (Lindou No.10) were inoculated with 1000 P. coffeae. The inoculated plants were kept in 1.5 L pots containing 1.2 L sterilized soil. Eight pots of uninoculated soybeans were used as the control. Ten weeks later, the inoculated roots were washed and brown lesions were observed. The number of nematodes/pot was approximately 7360 in soil and 796 in roots, and the reproduction factor was 8.16. Root-lesion nematodes and symptoms were not observed in control groups. P. coffeae has only been reported on soybean in Zhejiang (Wei et al. 2013) and Henan Province (Li et al. 2019) of China. To our knowledge, this is the first report of P. coffeae infecting soybean in Shandong Province, China. Since the root-lesion nematode can cause considerable damage to soybean, care should be taken to prevent the spread of P. coffeae to other regions in China.

First Report of Target Spot of Soybean caused by Corynespora cassiicola in the Colombian Eastern Plains

Soybean (Glycine max L. Merr.) is an important leguminous crop for Colombia, given the growing demand from the livestock, poultry, and aquaculture industries. About 80 percent of Colombian soybean production is in the State, or Department, of Meta, located in the Eastern Plains region, or Llanos Orientales, where the crop has an average yield of 2.5 t.ha-1 (FENALCE 2020). In July 2017, foliar symptoms, including rounded to irregular reddish-brown spots surrounded by a yellowish halo progressing to irregular spots with concentric rings, and in severe cases defoliation, were observed in a production field of Soyica P-34 soybean cultivar in Puerto López, Meta (Colombia). Dark brown lesions on stems and dark-brown to black spots on pods were also observed, and the incidence of symptomatic plants was recorded as 50%. Four infected plants were arbitrarily sampled from different locations across the field, and used for pathogen isolation. Specimen collection was conducted according to the permit conferred to AGROSAVIA under ANLAS' resolution No 1466 of December 03, 2014, Colombia. Symptomatic leaf pieces (~ 5 mm2 sizes) were rinsed with tap water for 1 min, dipped in a 0.5% sodium hypochlorite for 2 min and rinsed with sterile distilled water for 1 min, and then plated on potato dextrose agar (PDA, 39 g.L-1). Plates were incubated at 25°C for two weeks with a 12/12 h light/dark cycle using dark light. Four monoconidial isolates, with similar morphological characteristics, were obtained. Observations under the light microscope showed that conidia (n=50) were hyaline, elongated, 65-120 × 9-12 μm, with 3 to 10 pseudosepta, corresponding with those characteristics described for Corynespora cassiicola (Berk. & M. A. Curtis) C. T. Wei (Ellis and Holliday, 1971). Colonies, on PDA medium, were dark gray with abundant aerial mycelia growth. To confirm the morphological identification, extracted DNA from isolates AGSV13 and AGSV15 was used as a template to obtain partial sequences of the internal transcribed spacer (ITS) region of ribosomal DNA using the primer pair ITS 5/ITS 4 (White et al. 1990). Results from an NCBI-BLASTn search revealed that the ITS sequences (GenBank accessions MN298749 and MN298751) were 100% identical to those of C. cassiicola in GenBank (Accessions MN945374, AB873045). A phylogenetic analysis, using the maximum likelihood method, based on ITS sequences from voucher specimens of Corynespora spp. available at GenBank, revealed that the two isolates were placed in the same clade as C. cassiicola. Pathogenicity tests were conducted by spraying a conidial suspension (1 x 104 conidia.ml-1) of C. cassiicola AGSV13, onto young leaves (two to four true leaf stages) of 10 soybean plants (cv. Soyica P-34). Five plants were sprayed with sterile distilled water and served as non-inoculated control. All plants were incubated at high humidity for seven days at 28°C. Fungal inoculated plants showed typical foliar symptoms of brown spots surrounded by a yellowish halo, similar to those observed in the field. Disease symptoms were not observed on plants of the non-inoculated control. Fungal cultures were recovered from symptomatic leaves of all inoculated plants and verified as similar in morphology to the original C. cassiicola isolates, thus fulfilling Koch's postulates. Based on morphology, pathogenicity, and sequence data results, this is the first report of C. cassiicola causing Target spot on soybean in the Eastern Plains of Colombia and expands our knowledge of this disease. Target spot poses a threat to the expanding soybean crops in this country, as the range of yield losses due to this disease, in South America, has been estimated to be 8% to 42%, depending on the cultivar (Edwards Molina et al. 2019). These findings are significant to the soybean industry in Colombia and will be useful to provide better recommendations to growers for disease monitoring and management.

The occurrence of Pea enation mosaic virus 1 and Pea enation mosaic virus 2 from disease-affected pea fields in China

Pea (Pisum sativum L.) is an economically important legume crop that is commonly used as dry beans, fresh peas, pods and shoots (Guo et al. 2009). Pea enation mosaic is an important virus disease of pea caused by two viruses in an obligate symbiosis, pea enation mosaic virus 1 (PEMV-1, Enamovirus, Luteoviridae) and pea enation mosaic virus 2 (PEMV-2, Umbravirus, Tombusviridae) (Hema et al. 2014). In November 2019, foliar yellow mosaic and vein enations symptoms were observed from pea plants in five fields of Honghe autonomous prefecture, Yunnan province, China. Incidence of symptomatic plants ranged from 20 to 40% and was distributed in both small and large fields. Leaves with typical virus-like symptoms were collected from five symptomatic pea plants in two fields and used for total RNA extraction. The five extracts of equimolar quantities were pooled into a sample and subjected to High Throughput Sequencing (HTS) by Illumina HiSeq system. Analyses of raw RNA reads were performed using CLC Genomics Workbench 12 (Qiagen). A total of 60,009,746 RNA reads were obtained from the sample, and de novo assembly of the reads using the CLC Genomics generated 88,105 contigs. BLASTN searches revealed the presence of contigs with high similarities to PEMV-1, PEMV-2, Pea seed-borne mosaic virus, and Bean yellow mosaic virus. To confirm the presence of PEMV-1 and PEMV-2 in the samples, two virus-specific primer pairs were designed based on the contig sequences obtained by HTS in this study. Primer pairs PEMV-1F/PEMV-1R (5'-ATGCCGACTAGATCGAAATC-3'/5'-TCAGAGGGAGGCATTCATTA-3') that flank the cp gene of PEMV-1 and PEMV-2F/PEMV-2R (5'-ATGACGATAATCATTAATG-3'/5'-TCACCCGTAGTGAGAGGCA-3') that target the ORF3 region of PEMV-2 were used to amplify the two viruses in RT-PCR. DNA fragments of the expected sizes (PEMV-1, 570 bp; PEMV-2, 693 bp) were amplified from all five samples. The RT-PCR products were cloned and sequenced. Sequence analysis showed that the 570-bp amplicon (MT481989) shared the highest nucleotide sequence identity of 98.95% with PEMV-1 (Z48507), while the 693-bp fragment (MT481990) had the highest nucleotide sequence identity of 97.4% with PEMV-2 isolate JKI (MK948534). One gram of the symptomatic leaves from each of the five plants was homogenized with 5 mL of 0.01 M phosphate-buffered saline (PBS buffer), pH 7.0. Each of the resulted saps was used to inoculate onto five healthy pea seedlings. A total of 25 healthy pea seedlings were inoculated, and 16 inoculated plants developed yellowing and mottling at 10 days post inoculation (dpi); no symptoms were observed on control plants inoculated only with PBS buffer. The formation of the typical enation was observed along the veins of lower side of the symptomatic leaves of the inoculated plants at 30 dpi. PEMV-1 and PEMV-2 infection were confirmed by RT-PCR assays using the specific primer pairs described above. Although the presence of the pea enation mosaic virus complex was suspected in China based on symptomatology (Brunt et al. 1997), to our knowledge, this is the first molecular confirmation of PEMV-1 and PEMV-2 occurrence in China. The co-infection of PEMV-1 and PEMV-2 usually cause severe yield losses; therefore, integration of detection and control measures is important in pea production regions where the two viruses occurred.

Phytophthora cactorum as a Pathogen Associated with Root Rot on Alfalfa (Medicago sativa) in China

Alfalfa (Medicago sativa) is the largest grown pasture crop in China due to its economic and ecological importance. During the summer season from June to August in 2018, stunted plants was frequently observed in alfalfa fields that have been established for two years in Jinchang, Gansu Province. The disease incidence of root rot ranged from 40% to 50%. Taproots of stunted plants showed red-brown to dark brown discolorations, and lateral roots were poorly developed. Shoots wilted with rotted taproots and lateral roots in severely affected plants. Twenty symptomatic plants were collected and transported to the laboratory for pathogen isolations. Roots were washed under running tap water, cut into 2 to 3 mm pieces (40 pieces each plant), and then sterilized in 75% ethanol for 2 mins followed by three times washing with autoclaved distilled water. Surface dried pieces on autoclaved filter papers were put onto water agar and also a Phytophthora selective medium P5ARP(H) (Jeffers and Martin 1986). The plates were incubated at 22°C for 3 to 5 days and then the growing hypha were subcultured onto potato dextrose agar (PDA). Thirty-two Phytophthora-like isolates were obtained and showed similar morphologies on PDA. Five isolates picked randomly were purified by single-hyphal-tip and plugs (4 to 5 mm) from PDA cultures were incubated in petri dishes with autoclaved distilled water at 22°C for 5 days. Sporangia, chlamydospores and oospores were examined. Sporangia were usually ovoid and sometimes appeared ellipsoid, with the length of 30.5-39.1 μm and width of 23.4-27.8 μm. The diameter of chlamydospores was 29.6 to 42.5μm. Oospores had a diameter of 23.6 to 30.2 μm. The isolates were tentatively identified as P. cactorum based on these morphology characteristics (Montealegre et al. 2016). DNA of these isolates were extracted and PCR amplifications of the rDNA ITS region and cytochrome oxidase subunit I (Cox I) (Kroon et al. 2004) were conducted. Sequences of these isolates were then compared with reference sequences in GenBank using BLAST search. The 866-bp ITS sequences had a sequence identity of 99% to 100% with P. cactorum (e.g. accession nos. EU662221, KJ128036). In addition, the 663-bp CoxI sequences showed 100% sequence identity with three P. cactorum isolates (accession nos. AB688156, HQ708234, EU660851). The ITS and CoxI sequences of one representative isolate Phy.c2 have been deposited in GenBank with the accession no. MT280033 and MT344138, respectively. Pathogenicity of the five isolates (Phy.c1-Phy.c5) were determined on two-week-old alfalfa seedlings (cv. Longdong) grown from seeds. Inoculums were prepared by subculturing agar plugs from edges of PDA cultures into the flask with autoclaved millet seeds, and incubated at 22°C in darkness for two weeks and shaken by hand every two days to ensure uniform colonization. Seedlings were transplanted into pots (12 cm x 12 cm) filled with autoclaved potting mix infested with millet-seed inoculum of each isolate at a rate of 0.5% (w/w). Control seedlings for comparison were transplanted into pots with uninfested potting mix. There were five seedlings per pot and twelve replicate pots for both inoculated and noninoculated treatments, and pots were kept under controlled environment room (22°C, 12 h photoperiod and 65% relative humidity) that were watered every two days to free draining. 87%~92% of the inoculated plants showed stunted symptoms with poorly developed and brown-discoloured roots three weeks after inoculation while the control plants were healthy with no root disease symptoms. To fulfil Koch's postulates, re-isolated cultures from discoloured root tissues were confirmed as the inoculated isolates by morphological examination and ITS sequencing. The five-purified isolates were submitted to the Grassland Culture Collection Center, Lanzhou University, with the accession nos. LZU-MsR-Phy.c1-Phy.c5. To our knowledge, this is the first report of P. cactorum as a pathogen of root rot on alfalfa in China. Phytophthora spp. has been reported causing root rot on alfalfa in America, Australia and Canada, and other legumes such as chickpea, and many other crops worldwide (Musial et al. 2005; Tan and Tan 1986; Vandemark and Barker 2003), and P. cactorum was reported as a root rot pathogen on lavender in China (Chen et al. 2017). P. cactorum may be a significant pathogen associated with root rot in major commercial alfalfa-producing areas in China where are based on flood-irrigation during the growth season.

First report of Boeremia exigua var. exigua causing Black Spot-like symptoms on commercially grown soybean in Germany

Soybean (Glycine max [L.] Merr.) is economically the most important protein crop grown worldwide. However, Europe largely depends on soybean imported from the Americas (European Commission 2019; Haupt and Schmid 2020). In Germany, soybean production was not formally recorded before 2016, but since then a steady increase along with an expansion of the growing area from the south of Germany to northern states occurred. In 2019 an area of 29,000 hectares was under soybean cultivation (Federal Ministry of Food and Agriculture (Germany) 2019). In the state of North Rhine-Westphalia (NRW, western part of Germany) farmers have started in recent years to cultivate soybean, making it increasingly important to monitor pathogens associated with this new crop. At the beginning of October 2019, shortly before harvest, rows of black spots on pods and stems of soybean plants cv. Viola throughout a field site near Jülich (NRW) were observed. Close observation identified them as pycnidia with similarity to symptoms reported from soybean in Austria in 2015 (Hissek and Bedlan 2016). The collected samples were thoroughly surface sterilized (two washes with 70 % EtOH, a rinse in 0.5 % sodium hypochlorite solution and a final wash in sterile double distilled water) and placed on plates containing potato dextrose agar (PDA) at 22 °C in the dark. Fungal colonies were transferred to malt extract agar plates (MEA) and examined by microscopy. Thus, 34 of 41 isolates looked morphologically similar, producing colonies that appeared dark grey with white aerial mycelium and round to irregular margins. A single spore isolate was generated and designated IPP1903. Spores derived from IPP1903 were unicellular and mostly oblong to cylindrical with a mean width of 2.6±0.3 µm and a mean length of 5.9±0.8 µm (N=50, mean value ± standard deviation). Colonies on MEA were 5.4 to 5.8 cm in diameter after growth for seven days at 20 to 25°C with a photoperiod of 12 h and 3.3 to 3.7 cm in diameter after growth for seven days in the dark at 22°C. These morphological observations led to the conclusion that the isolate may belong to the genus Phoma. To test this hypothesis, we performed a drop test with 5 M NaOH which is used routinely to check for the presence of a genus-specific metabolite. We observed a change in color, indicating a positive test result. The color change was even more pronounced on the plates incubated in the light, further confirming the presence of "metabolite E" (Boerema et al. 2004; Kövics et al. 2014). Next, DNA was extracted and PCR was performed with primers specific for ITS regions (GenBank MT397284), LSU (MT397285), rbb2 (MT414713) or tub2 (MT414712). Sequencing results of PCR products were used to create a combined phylogenetic tree, including sequences published previously (Chen et al. 2015). Our sequencing results together with the morphological observations clearly identified the fungal isolate to be Boeremia exigua var. exigua. The isolate is publicly available in the CBS collection of the Westerdijk Fungal Biodiversity Institute with the accession no. CBS 146730. Koch's postulates were fulfilled by inoculating a spore suspension of the isolate IPP1903 (5x105 ml-1 in 0.05% Tween 20 solution in distilled water) onto healthy primary leaves of twenty 14 days old soybean plants of the cultivar Abelina. While the mock-inoculated plants (inoculated with 0.05% Tween 20 solution in distilled water) stayed healthy, the inoculated plants developed lesions on the leaves after seven days. Six weeks after inoculation the fungus could be reisolated from cuttings of the infected leaves after surface-sterilization. Fungal colonies were confirmed to be B. exigua var. exigua by morphological examination and via NaOH drop test. To our knowledge, this is the first report of B. exigua var. exigua causing disease on commercially grown soybean in Germany.

First report of vicia cryptic virus M infecting cowpea (Vigna unguiculata) in China

Cowpea (Vigna unguiculata) is a crop grown worldwide as a protein source for food and feed (Lonardi et al. 2019). During the summer of 2019, noticeable virus-like symptoms such as mosaic, leaf narrowing, stunt and chlorosis were observed on cowpeas 'Xianfeng' planted in Yangzhou city and its suburbs, Jiangsu Province, East China (Supplementary Fig. S1A). The total RNA was extracted from both symptomatic and asymptomatic plants by RNAiso Plus (TaKaRa, Dalian, China) and sRNAs were separated and recovered by gel purification. The NEBNext Ultra II RNA Library Prep Kit for Illumina (NEB, UK) was used for sRNA library construction. The library was sequenced with the paired-end method on the Illumina Hiseq 2000 platform (Sangon, Shanghai, China). The obtained sequencing files were treated with Illumina's CASAVA pipeline (version 1.8). The reads resulting from sequencing were further processed with adaptor removing, and the most abundant sRNAs were distributed from 21-24 nt (Supplementary Fig. S1B). The de novo assembly was performed with the Velvet Software 0.7.31 (k=17), and the obtained contigs (∼12,000, Contigs > 500 bp) were used perform a BLAST search against the GenBank viral reference database. Fifteen contigs with high similarities of 98.61% to 99.64% and coverage of 94% to the reported vicia cryptic virus M (VCV-M) genomic sequence (GenBank accession No. EU371896) were identified. Other common viruses, such as cowpea mosaic virus (CPMV), cowpea aphid-borne mosaic virus (CABMV), and cucumber mosaic virus (CMV), were also included (Unpublished).VCV-M belongs to the genus Amalgavirus, family Amalgaviridae (Nibert et al. 2016). Amalgaviruses are efficiently transmitted through seeds but not mechanically or by grafting (Sabanadzovic et al. 2009). To confirm the presence of VCV-M in the collected plants, total RNA was isolated and the first-strand cDNA was prepared by M-MLV reverse transcriptase (TaKaRa, Dalian, China) using specific primers. Primers (Supplementary Table SI) were designed according to the assembled contigs. Polymerase chain reaction (PCR) was performed to amplify the targeted genomic fragment of VCV-M, and the predicted 3,434 bp amplicon was obtained from five cowpea plants (Supplementary Fig. S1C). A randomly selected amplicon was purified with the TIANgel Midi Purification Kit (Tiangen, Beijing, China) and cloned to pMD19-T (TaKaRa, Dalian, China) for sequencing (Sangon, Shanghai, China). The obtained consensus sequence (GenBank accession No. MN015673) was analyzed and showed 99.39% similarity with the reported VCV-M genome (GenBank accession No. EU371896). To confirm the occurrence and distribution of VCV-M infection, 17 cowpea samples of different cultivars (4 with yellowing and stunt symptoms and 13 without visible symptoms) were collected from different regions of Jiangsu Province and tested using RT-PCR with specific primers (Supplementary Fig. S1C). They were further tested by western blot (WB) detection as described previously (Zhang et al. 2017). Specific CPVCV-M antiserum was obtained by immunizing the New Zealand white rabbits with the prokaryotic expressed recombinant His-CPVCV-M protein (HuaBio, Hangzhou, China). WB results (Supplementary Fig. S1D) and RT-PCR resulted in five samples that were positive out of a total of 17 samples, suggesting the VCV-M infection is common in cowpea plants. To determine whether the VCV-M was the causal agent or contributor to the observed symptoms, we investigated the presence of other cowpea-infecting viruses (CPMV, CABMV, and CMV) in these samples through RT-PCR with specific primers for each virus (Supplementary Table SI) and ELISA with commercial kits. RT-PCR and ELISA detection results showed mixed infection by VCV-M/CPMV (n = 1), VCV-M/CABMV (n = 1), VCV-M/CMV (n = 1), or VCV-M/CPMV/CABMV/CMV (n = 2). The VCV-M/CABMV co-infected sample was asymptomatic. Taken together, the symptoms on cowpea could not be attributed to one particular viral infection. To further confirm VCV-M infection, we selected four samples (two positive and two negative, as determined by RT-PCR and WB) for northern blot assay. The probe was prepared with the DIG Random Labeling and Detection Kit I (POD) for color detection with DAB (BOSTER, Wuhan, China). The Northern blot assay was performed as previously described with minor modifications (Prosniak et al. 2001). The results (Supplementary Fig. S1E) confirmed the accuracy of previous RT-PCR and WB analyses. To our knowledge, this is the first report of VCV-M infection of cowpea plants in China. Although it is commonly accepted that VCV-M causes no symptoms, the roles of such viruses in affecting their hosts' biological characteristics, which are often influenced by co-infection conditions, remains unclear.