An Emerging Strawberry Fungal Disease Associated with Root Rot, Crown Rot and Leaf Spot Caused by Neopestalotiopsis rosae in Mexico

Preventive and Curative Effects of Treatments to Manage Strawberry Root and Crown Rot Caused by Neopestalotiopsis rosae

Strawberry root and crown rot caused by the fungus Neopestalotiopsis rosae is an emerging disease that has caused yield losses of up to 70% in Mexico and other regions worldwide. This research evaluated the effects of biological and chemical fungicides applied as preventive and curative applications for controlling root and crown rot caused by N. rosae in strawberries under greenhouse conditions. Treatments included these chemical fungicides: prochloraz, prochloraz + thiram, cyprodinil + fludioxonil, difenoconazole + azoxystrobin, iprodione, captan, thiram, pydiflumetofen + fludioxonil, fluxapyroxad + pyraclostrobin, and hymexazol; each was applied at commercial doses. Also tested were biological treatments based on Trichoderma koningiopsis, T. asperellum, Streptomyces sp., and Bacillus amyloliquefaciens strain D747 (B. velezensis). Disease incidence, severity, plant mortality, root length, and dry weight were determined. Results showed that overall, preventive applications of the fungicides pydiflumetofen + fludioxonil, cyprodinil + fludioxonil, and prochloraz resulted in the smallest area under the disease progress curve and the lowest final disease incidence, severity, and plant mortality. An intermediate group of effective treatments entailed hymexazol, iprodione, T. asperellum, and T. koningiopsis (50 to 75% efficacy). Treatments with greater efficacy (99 to 100%), pydiflumetofen + fludioxonil, cyprodinil + fludioxonil, and prochloraz, also had maximal total plant biomass vis-à-vis the untreated control. By contrast, each treatment's efficacy was significantly reduced when applied curatively (0 to 37% treatment efficacy). These results suggest that certain treatments are useful for controlling strawberry root and crown rot caused by N. rosae when applied preventively (as root dipping). These results will contribute to designing more effective management programs for root and crown rot caused by N. rosae on strawberry.

First report of Neopestalotiopsis rosae causing leaf blight on Shatangju in southern China

Shatangju (Citrus reticulata Blanco cv. Shatangju) belongs to genus Citrus and was cultivated extensively in southern China. In April 2022, a leaf blight-like symptom (firstly brown spots appeared on infecting leaves, then these brown spots extended, finally the whole leaves displayed blight-like symptom) was observed on 5%~10% of Shatangju seedlings (around five hundreds in total) in an orchard located in Wuhan city, Hubei, China. Diseased leaves from three seedlings were collected and cut into pieces (0.2 to 0.5 cm). These pieces were surface-sterilized using 75% ethanol for 3 min, rinsed with sterile distilled water for several times, then placed on potato dextrose agar (PDA) and incubated at 26°C with 12-h light/dark cycle. Over 20 pieces plated, wherein 30% were identified as Colletotrichum fructicola, 60% as Neopestalotiopsis spp., and 10% developed saprophytes. C. fructicola was a known pathogen on citrus, thus Neopestalotiopsis spp. was further investigated. Eight single-conidium colonies of the Neopestalotiopsis spp. were obtained, wherein STJ-8 was chosen as a representative for further study. The average growth rate of STJ-8 was 15.1±0.5 mm/day (n=5). Fungal colonies produced white cottony mycelium with abundant black acervuli distributed in concentric rings 6-8 days after planting, which ranged from 342.3 to 710.5 μm in diameter (n=100). Conidia were fusoid, five cells, four septa with average dimensions of 25.36×5.47 μm (n=100). Basal and apical cells were hyaline, wherein three middle cells were brown with darker septa. The apical cell was cylindrical with two to three transparent accessory filaments (13.7 to 30.5 µm in length, n=80). Basal cell was conic with an appendage (4.1 to 8.8 µm in length, n=40). Partial sequences of internal transcribed spacer (ITS), translation elongation factor 1-alpha (TEF-1α), and β-tubulin (TUB2) were amplified with reported primers (White et al. 1990; Lee et al. 2006; Maharachchikumbura et al. 2014), sequenced, and submitted to GenBank (accession nos. ITS: OP236541; TEF-1α: OP250124; TUB2:OP263094). BLASTn results showed 100% identity with the corresponding sequences of Neopestalotiopsis rosae. A multilocus phylogenetic analysis showed STJ-8 was closest to N. rosae. Thus, STJ-8 was identified as N. rosae. Pathogenicity tests were performed on one-year-old Shatangju seedlings and detached primary leaves by inoculating needle-wounded leaves with seven days old 5-mm mycelial plugs/acervuli (about 5000 spores) of STJ-8. Control seedlings/leaves were inoculated with 5-mm PDA plugs/sterile water drops. All inoculated detached leaves were cultured at same the place with STJ-8 cultured, while inoculated seedlings were put in a growth chamber at 26°C under a 16-h light/dark cycle (60% humidity). Symptoms developed on all inoculated leaves (except healthy control) 2 and 4 days post-inoculation by mycelial plugs and acervuli, respectively. N. rosae was re-isolated from the inoculated leaves, confirming Koch's postulates. N. rosae has been reported to cause diseases on various plants worldwide (Rebollar-Alviter et al. 2020; Xavier et al. 2021; Lawrence et al. 2022). In China, N. rosae has been reported to cause leaf spot/blight on pecan and strawberry (Wu et al. 2021; Gao et al. 2022), which caused great loss on these crops. To our knowledge, this is the first report of N. rosae causing leaf disease on citrus. Our study is important for developing control strategies against N. rosae in future.

Diversity of Sporocadaceae (pestalotioid fungi) from Rosa in China

Rosa (Rosaceae) is an important ornamental and medicinal plant genus worldwide, with several species being cultivated in China. Members of Sporocadaceae (pestalotioid fungi) are globally distributed and include endophytes, saprobes but also plant pathogens, infecting a broad range of host plants on which they can cause important plant diseases. Although several Sporocadaceae species were recorded to inhabit Rosa spp., the taxa occurring on Rosa remain largely unresolved. In this study, a total of 295 diseased samples were collected from branches, fruits, leaves and spines of eight Rosa species (R. chinensis, R. helenae, R. laevigata, R. multiflora, R. omeiensis, R. rugosa, R. spinosissima and R. xanthina) in Gansu, Henan, Hunan, Qinghai, Shaanxi Provinces and the Ningxia Autonomous Region of China. Subsequently 126 strains were obtained and identified based on comparisons of DNA sequence data. Based on these results 15 species residing in six genera of Sporocadaceae were delineated, including four known species (Pestalotiopsis chamaeropis, Pes. rhodomyrtus, Sporocadus sorbi and Spo. trimorphus) and 11 new species described here as Monochaetia rosarum, Neopestalotiopsis concentrica, N. subepidermalis, Pestalotiopsis tumida, Seimatosporium centrale, Seim. gracile, Seim. nonappendiculatum, Seim. parvum, Seiridium rosae, Sporocadus brevis, and Spo. spiniger. This study also represents the first report of Pes. chamaeropis, Pes. rhodomyrtus and Spo. sorbi on Rosa. The overall data revealed that Pestalotiopsis was the most prevalent genus, followed by Seimatosporium, while Pes. chamaeropis and Pes. rhodomyrtus were the two most prevalent species. Analysis of Sporocadaceae abundance on Rosa species and plant organs revealed that spines of R. chinensis had the highest species diversity. Citation: Peng C, Crous PW, Jiang N, et al. 2022. Diversity of Sporocadaceae (pestalotioid fungi) from Rosa in China. Persoonia 49: 201-260. https://doi.org/10.3767/persoonia.2022.49.07.

First Report of Neopestalotiopsis rosae Causing Crown and Root Rot of Strawberry in California

Strawberry production in California represents over 38,000 acres with an annual farm value of $1.99 billion. Strawberry dieback was observed in February of 2021 in the Salinas Valley in central California. Disease symptoms included dead and dying 'Maverick' strawberry plants with necrotic lesions and black discoloration of the crown, root cortex, epidermis, and vascular tissues. Disease incidence was estimated to be 60% of a 20-acre field. The causal agent was isolated from five randomly selected symptomatic plants by surface disinfesting symptomatic crowns and roots in 1% sodium hypochlorite for 30 s, rinsed twice in sterile water for 30 s then placed on 3.7% potato dextrose agar (PDA) Petri dishes amended with 100 mg/L streptomycin, and then incubated for 7 days at 24°C under a 12-h photoperiod. Consistent white cottony fungal colonies were hyphal tip transferred to fresh PDA dishes and incubated as above for morphological and genetic comparisons. Black acervuli developed 7 to 9 days after incubation. Conidia were ellipsoidal, measuring 25 to 30 × 7.5 to 10 µm (average 26.8 × 9.2 µm, n = 30), with five cells. Apical and basal cells were hyaline, and the three median cells were versicolorous brown, with a single, straight, centric basal appendage and 3 to 4 flexuous apical appendages. Colony diameter averaged 90 mm in 7 days. Based on colony and conidial characters, the fungus was tentatively identified as a species of Neopestalotiopsis (Maharachchikumbura et al. 2014). Total genomic DNA was extracted from three axenic cultures using the Invitrogen Easy-DNA kit. Three genetic loci were PCR amplified and sequenced: internal transcribed spacer (ITS), beta-tubulin (BT), and translation elongation factor 1-alpha (TEF) utilizing the primer pairs ITS1/ITS4, T1/Bt2a, and EF1-688F/EF1-1251R, respectively (White et al. 1990, O'Donnell and Cigelnik 1997, Glass and Donaldson 1995, and Alves et al. 2008). A BLASTn search of NCBI showed 99.6% identity (495/497 bases; OM942910-OM942912) with the type specimen of Neopestalotiopsis rosae CBS 101057 for the ITS locus. Both BT (765/765 bases, OM964802-OM964804) and TEF (475/475 bases; OM964799-OM964801) sequences were 100% identical to CBS 101057. Conidia of isolate PAR027 were scraped from the surface of 14-day-old PDA Petri dishes and inoculated (1 × 106 spores/mL: 2 mL/plant) to four apparently healthy strawberry transplant roots of the cultivar 'Monterey' in 'sunshine mix' potting soil. Two control plants were inoculated with sterile water. The experiment was conducted twice. Strawberry plants were maintained in a hoop house for four weeks, after which dieback and wilt symptoms resembled the symptoms observed in the field. Control plants remained asymptomatic and no pathogens were isolated. Fungal recovery from inoculated plants morphologically matched the original inoculum; thus, Koch's postulates was satisfied. To our knowledge, this is the first report of N. rosae causing crown and root rot disease of strawberry in California. Previously, N. rosae has been reported to cause serious decline of strawberry plants in Florida and several countries (Baggio et al. 2021, Rebollar-Alviter et al. 2020, Wu et al. 2021, Sun et al. 2021). Correct identification of the causal agent provides a proper foundation to identify control strategies for this emerging disease, which has the potential to become a significant problem for strawberry growers in the Salinas Valley of California.

Neopestalotiopsis siciliana sp. nov. and N. rosae Causing Stem Lesion and Dieback on Avocado Plants in Italy

Avocado (Persea americana) represents an important emerging tropical crop in Italy, especially in the southern regions. In this study, young plants of avocado showing symptoms of stem and wood lesion, and dieback, were investigated. Isolations from symptomatic tissues consistently yielded colonies of Neopestalotiopsis-like species. The characterization of representative isolates was based on the observation of morphological characters, the effect of temperature on mycelial growth rate, and on the sequencing of three different gene regions, specifically ITS, TEF1, and TUB2. Phylogenetic analyses were conducted based on maximum parsimony and maximum likelihood approaches. The results showed the presence of two species, viz. Neopestalotiopsis rosae and N. siciliana, the latter of which is here described as a new species. Pathogenicity tests were conducted using the mycelial plug technique on young potted avocado trees for both Neopestalotiopsis species. The results showed that both species were pathogenic to avocado. This study represents the first report of these two species affecting avocado and results in the description of a new species within the genus Neopestalotiopsis. Based on phylogeny, Pestalotiopsis coffeae-arabicae is combined in Neopestalotiopsis.

Diversity, Pathogenicity, and Fungicide Sensitivity of Fungal Species Associated with Late-Season Rots of Wine Grape in the Mid-Atlantic United States

Late-season bunch rots cause major losses in grape production every year in the Mid-Atlantic United States, but the causal agents are not well characterized. In this study, 265 fungal isolates were collected from rotten grapes from 2014 to 2020 and identified to the genus level according to internal transcribed spacer sequences. The most prevalent of the 15 genera were Botrytis, Colletotrichum, Aspergillus, Alternaria, Pestalotiopsis, and Neopestalotiopsis. Of these, isolates within three prevalent, yet understudied, genera were identified to be Aspergillus uvarum, Alternaria alternata, and Neopestalotiopsis rosae. The pathogenicity of these three fungal species was evaluated in two field trials by artificially inoculating wounded and nonwounded grapes (Vitis vinifera) of four cultivars at the phenological stages of bloom, véraison, and preharvest. Upon ripening, fruit were weighed and assessed for severity of multiple diseases. On nonwounded fruit, A. uvarum caused significantly higher disease severity than the control in both seasons. On wounded fruit, each inocula caused significantly higher disease than the respective controls in the first season, but only A. uvarum and Botrytis cinerea caused this in the second season. Also, wounding was found to have a detrimental effect on cluster weight, which was significantly influenced by inoculation timing and cultivar. Lastly, A. uvarum and N. rosae were tested for sensitivity to azoxystrobin, boscalid, and difenoconazole. The A. uvarum isolates were found to be more sensitive to boscalid and difenoconazole in general, with varying sensitivity to azoxystrobin. N. rosae isolates were resistant to boscalid and azoxystrobin but displayed much higher sensitivity to difenoconazole. Evidence from the isolate collection and field trials demonstrates that A. uvarum could be a significant pathogen of wine grapes in the Mid-Atlantic United States. Results from this study will be useful for the identification and management of the understudied Alternaria, Aspergillus, and Neopestalotiopsis fruit rots of wine grapes.

Detection of Strawberry Diseases Using a Convolutional Neural Network

The strawberry (Fragaria × ananassa Duch.) is a high-value crop with an annual cultivated area of ~500 ha in Taiwan. Over 90% of strawberry cultivation is in Miaoli County. Unfortunately, various diseases significantly decrease strawberry production. The leaf and fruit disease became an epidemic in 1986. From 2010 to 2016, anthracnose crown rot caused the loss of 30–40% of seedlings and ~20% of plants after transplanting. The automation of agriculture and image recognition techniques are indispensable for detecting strawberry diseases. We developed an image recognition technique for the detection of strawberry diseases using a convolutional neural network (CNN) model. CNN is a powerful deep learning approach that has been used to enhance image recognition. In the proposed technique, two different datasets containing the original and feature images are used for detecting the following strawberry diseases—leaf blight, gray mold, and powdery mildew. Specifically, leaf blight may affect the crown, leaf, and fruit and show different symptoms. By using the ResNet50 model with a training period of 20 epochs for 1306 feature images, the proposed CNN model achieves a classification accuracy rate of 100% for leaf blight cases affecting the crown, leaf, and fruit; 98% for gray mold cases, and 98% for powdery mildew cases. In 20 epochs, the accuracy rate of 99.60% obtained from the feature image dataset was higher than that of 1.53% obtained from the original one. This proposed model provides a simple, reliable, and cost-effective technique for detecting strawberry diseases.

First Report of Neopestalotiopsis rosae Causing Leaf Blight and Crown Rot on Strawberry in Taiwan

For the past 30 years, the most predominant strawberry cultivar in Taiwan has been 'Taoyuan No. 1', which produces fruit with rich flavor and aroma but is highly susceptible to anthracnose (Chung et al. 2019). Because epidemics of anthracnose became more destructive, farmers switched to an anthracnose-tolerant cultivar 'Xiang-Shui' (~50% and ~80% of the cultivation area in 2018 and 2019, respectively). Since 2018, severe leaf blight and crown rot symptoms have been observed all year in 'Xiang-Shui' in Miaoli, Nantou, Hsinchu, Taipei, Taoyuan, and Chiayi Counties. The disease became more prevalent and severe during 2019 to 2020 and caused up to 30% plant loss after transplanting. Symptoms appeared as brown necrotic lesions with black acervuli on leaves, slightly sunken dark-brown necrosis on stolons, and sunken reddish-brown necrosis on fruit. The diseased crown tissue showed marbled reddish-brown necrosis with a dark-brown margin, and plants with severe crown rot usually showed reddish-brown discoloration on leaves (the leaves initially turned reddish-brown between the veins and could become entirely scorched at later stages). To isolate the causal agent, small fragments of diseased leaves, crowns, stolons, and fruits were surface-disinfested with 0.5% sodium hypochlorite for 30 seconds, rinsed with sterile water then placed on 1.5% water agar. Single hyphal tips extended from tissues were transferred to potato dextrose agar and cultured for 7 days at 25°C under a 12-h/12-h photoperiod. Total 20 isolates were obtained from diseased leaves, crowns, stolons, and fruits. Colonies were white with cottony aerial mycelium, irregular margins, and black acervuli distributed in concentric rings. Conidia were fusiform to ellipsoid (five cells) with one basal appendage and three or four (usually three) apical appendages. From colony and conidial morphology, the causal agent was identified as Neopestalotiopsis sp. (Maharachchikumbura et al. 2014). The internal transcribed spacer (ITS) region, β-tubulin (TUB), and translation elongation factor 1-alpha (TEF-1α) of three isolates (ML1664 from diseased crown tissue collected in Hsinchu County; ML2147 and ML2411 from diseased leaves collected in Miaoli County) were sequenced (GenBank nos. MT469940 to MT469948). All three isolates clustered with the ex-type strain of Neopestalotiopsis rosae in the multilocus (ITS+TUB+TEF-1α) phylogenetic tree. To fulfill Koch's postulates, spore suspensions of ML1664 and ML2147 at 1×106 conidia/mL were used to spray-inoculate 'Xiang-Shui' seedlings at the 3 to 4 leaf stage until run-off (two trials, five seedlings per trial). Inoculated plants were put in a plastic bag (> 90% RH) at 25°C under a 12-h/12-h photoperiod. After 10-14 days, 80% of inoculated plants showed leaf or crown symptoms similar to those in the field. Control plants sprayed with sterile water showed no symptoms (4-5 seedlings per trial). The fungi were re-isolated from necrotic lesions with 100% frequency (n ≥ 3 isolates per trial), and morphological characters and ITS sequences were identical to the original ones. This is the first report of N. rosae causing leaf blight and crown rot in strawberry in Taiwan. N. rosae and N. clavispora have been reported as new threats to strawberry in several other countries (Rebollar-Alviter 2020; Gilardi 2019). Clarification of the pathogen provides a basis for developing strategies to control the emerging disease. Further studies are needed to evaluate the resistance/susceptibility of major strawberry cultivars and the fungicide sensitivity of the pathogen.