Shoot Blight on Chinese Fir (Cunninghamia lanceolata) is Caused by Bipolaris oryzae

Bipolaris fujianensis sp. nov., an Emerging Pathogen of Sapling Shoot Blight on Chinese Fir, and Its Sensitivity to Fungicides

Chinese fir is an extremely important economic tree species in southern China. In recent years, 74.5% of Chinese fir saplings suffered from shoot blight in Shunchang County, Nanping City, Fujian Province, China. Seventeen isolates were collected from rotten shoots, and their pathogenicity was confirmed following Koch's postulates. The five pathogenic isolates were identified as belonging to the genus Bipolaris based on morphological characteristics, including septate and geniculate conidiophores, smooth to slightly verruculose conidiogenous nodes, dematiaceous phragmospore conidia, oblong or fusiform conidia, and slightly protruding or truncate hilum on conidia, but the number of pseudosepta (3 to 11, mostly 5 to 8) and the size of conidia ([22.81 to 116.13] × [9.16 to 26.58] μm) are different from those of the known species of Bipolaris. A phylogenetic analysis based on ITS, GAPDH, and Tef1-α sequences determined that the five strains belong to a new species of Bipolaris, and the name Bipolaris fujianensis sp. nov. is proposed. The fungicide sensitivity of the pathogen strain Cfsb3 was further evaluated using eight fungicides. Flusilazole, difenoconazole, tebuconazole, and propiconazole exhibited high toxicity to Cfsb3, and the effective concentration inhibiting 50% (EC50) of mycelial growth was 0.08, 0.20, 0.34, and 0.36 μg/ml, respectively, for these four fungicides. Flusilazole, difenoconazole, and iprodione inhibited B. fujianensis by 100% on detached Chinese fir shoots at their recommended concentrations, but azoxystrobin and thiram were ineffective. In conclusion, this study reported an emerging pathogen of Chinese fir sapling shoot blight and proposed triazole and dicarboximide fungicides for disease control.

Morphological and phylogenetic analyses reveal three new species of Fusarium (Hypocreales, Nectriaceae) associated with leaf blight on Cunninghamialanceolata in China

Chinese fir (Cunninghamialanceolata) is a special fast-growing commercial tree species in China with high economic value. In recent years, leaf blight disease on C.lanceolata has been observed frequently. The diversity of Fusarium species associated with leaf blight on C.lanceolata in China (Fujian, Guangxi, Guizhou, and Hunan provinces) was evaluated using morphological study and molecular multi-locus analyses based on RNA polymerase second largest subunit (RPB2), translation elongation factor 1-alpha (TEF-1α), and RNA polymerase largest subunit (RPB1) genes/region as well as the pairwise homoplasy index tests. A total of five Fusarium species belonging to four Fusarium species complexes were recognized in this study. Two known species including Fusariumconcentricum and F.fujikuroi belonged to the F.fujikuroi species complex, and three new Fusarium species were described, i.e., F.fujianense belonged to the F.lateritium species complex, F.guizhouense belonged to the F.sambucinum species complex, and F.hunanense belonged to the F.solani species complex. To prove Koch's postulates, pathogenicity tests on C.lanceolata revealed a wide variation in pathogenicity and aggressiveness among the species, of which F.hunanense HN33-8-2 caused the most severe symptoms and F.fujianense LC14 led to the least severe symptoms. To our knowledge, this study also represented the first report of F.concentricum, F.fujianense, F.fujikuroi, F.guizhouense, and F.hunanense causing leaf blight on C.lanceolata in China.

Seven new species of Alternaria (Pleosporales, Pleosporaceae) associated with Chinese fir, based on morphological and molecular evidence

Chinese fir (Cunninghamialanceolata) is a special fast-growing commercial tree species in China and has significant ecological and economic value. However, it experienced damage from leaf blight caused by pathogenic fungi of the genus Alternaria. To determine the diversity of Alternaria species associated with leaf blight of Chinese fir in China, infected leaves were collected from five major cultivation provinces (Fujian, Henan, Hunan, Jiangsu and Shandong provinces). A total of 48 fungal strains of Alternaria were obtained. Comparison of morphology and phylogenetic analyses, based on nine loci (ITS, SSU, LSU, GAPDH, RPB2, TEF1, Alt a1, endoPG and OPA10-2) of the representative isolates as well as the pairwise homoplasy index tests, revealed that the fungal strains belonged to seven undescribed taxa of Alternaria, which are described here and named as Alternariacunninghamiicolasp. nov., A.dongshanqiaoensissp. nov., A.hunanensissp. nov., A.kunyuensissp. nov., А. longqiaoensissp. nov., A.shandongensissp. nov. and A.xinyangensissp. nov. In order to prove Koch's postulates, pathogenicity tests on detached Chinese fir leaves revealed significant pathogenicity amongst these species, of which A.hunanensis is the most pathogenic to Chinese fir. This study represents the first report of A.cunninghamiicola, A.dongshanqiaoensis, A.hunanensis, A.kunyuensis, A.longqiaoensis, A.shandongensis and A.xinyangensis causing leaf blight on Chinese fir. Knowledge obtained in this study enhanced our understanding of Alternaria species causing leaf blight on Chinese fir and was crucial for the disease management and the further studies in the future.

A real-time PCR for detection of pathogens of anthracnose on Chinese fir using TaqMan probe targeting ApMat gene

BACKGROUND

Anthracnose is one of the most widespread and destructive diseases on Chinese fir. Colletotrichum cangyuanense, Colletotrichum fructicola, Colletotrichum gloeosporioides, and Colletotrichum siamense are the causal agents of anthracnose on Chinese fir. A rapid and accurate diagnosis of different pathogens is critical for the disease management.

RESULTS

Phylogenetic tree and sequence similarity analysis showed that the single-locus ApMat provides superior phylogenetic information and is an appropriate target to distinguish C. cangyuanense, C. fructicola, C. gloeosporioides, and C. siamense. The real-time PCR assays with the primer sets of MQ-F/R, 1#C-F/R, YK-F/R, and WZ-F/R, and corresponding TaqMan probes of MQ-P, 1#C-P, YK-P, and WZ-P were specific for C. cangyuanense, C. fructicola, C. gloeosporioides, and C. siamense, respectively. The sensitivity tests showed that the lowest amount of gDNA that the PCRs can detect was 1 ng of genomic DNA. The validity of the assays was confirmed by directly detecting the pathogens from both the fungal culture and infected Chinese fir.

CONCLUSION

These results demonstrated the potential of the TaqMan real-time PCR targeting the ApMat gene to provide rapid, specific, and reliable molecular detection of C. fructicola, C. gloeosporioides, C. siamense, and C. cangyuanense, respectively. The data also provided a reference solution for the identification of species within Colletotrichum gloeosporioides species complex (CGSC), which share similar morphological characteristics. © 2022 Society of Chemical Industry.

Whole genome sequencing of Clarireedia aff. paspali reveals potential pathogenesis factors in Clarireedia species, causal agents of dollar spot in turfgrass

Dollar spot is one of the most damaging diseases in turfgrass, reducing its quality and playability. Two species, Clarireedia monteithiana and C. jacksonii (formerly Sclerotinia homoeocarpa) have been reported so far in the United States To study the Clarireedia genome, two isolates H2 and H3, sampled from seashore paspalum in Hawaii in 2019 were sequenced via Illumina paired-end sequencing by synthesis technology and PacBio SMRT sequencing. Both isolates were identified as C. aff. paspali, a novel species in the United States Using short and long reads, C. aff. paspali H3 contained 193 contigs with 48.6 Mbp and presented the most completed assembly and annotation among Clarireedia species. Out of the 13,428 protein models from AUGUSTUS, 349 cytoplasmic effectors and 13 apoplastic effectors were identified by EffectorP. To further decipher Clarireedia pathogenicity, C. aff. paspali genomes (H2 and H3), as well as available C. jacksonii (LWC-10 and HRI11), C. monteithiana (DRR09 and RB-19) genomes were screened for fifty-four pathogenesis determinants, previously identified in S. sclerotiorum. Seventeen orthologs of pathogenicity genes have been identified in Clarireedia species involved in oxalic acid production (pac1, nox1), mitogen-activated protein kinase cascade (pka1, smk3, ste12), appressorium formation (caf1, pks13, ams2, rgb1, rhs1) and glycolytic pathway (gpd). Within these genes, 366 species-specific SNPs were recorded between Clarireedia species; twenty-eight were non-synonymous and non-conservative. The predicted protein structure of six of these genes showed superimposition of the models among Clarireedia spp. The genomic variations revealed here could potentially lead to differences in pathogenesis and other physiological functions among Clarireedia species.

The Fungal Endophyte Epicoccum dendrobii as a Potential Biocontrol Agent Against Colletotrichum gloeosporioides

Anthracnose caused by Colletotrichum gloeosporioides is one of most serious fungal diseases on Chinese fir (Cunninghamia lanceolata). Eight fungal endophytes were isolated from a young heathy branch of Chinese fir and screened against the pathogen in vitro. One isolate, designated as SMEL1 and subsequently identified as Epicoccum dendrobii based on morphological and phylogenetic analyses, suppressed mycelial growth of Colletotrichum gloeosporioides on dual-culture plates. Additionally, E. dendrobii metabolites significantly decreased the biomass of Colletotrichum gloeosporioides. E. dendrobii was able to enter the internal tissues of the host plant via stomatal cells. Metabolites of E. dendrobii significantly inhibited conidial germination and appressorium formation, which at least partly explained why the endophyte significantly inhibited lesion development caused by Colletotrichum gloeosporioides on various host plants. We further confirmed that some components with antifungal activity could be extracted from E. dendrobii using ethyl acetate as an organic solvent. To our knowledge, this is the first report of E. dendrobii as a potential biocontrol agent against a fungal phytopathogen.

Antifungal Effects of Volatile Organic Compounds Produced by Rahnella aquatilis JZ-GX1 Against Colletotrichum gloeosporioides in Liriodendron chinense × tulipifera

The use of volatile organic compounds (VOCs) produced by microorganisms for the biological control of plant diseases has attracted much attention in recent years. In this study, the antifungal activity and identity of VOCs produced by Rahnella aquatilis JZ-GX1 isolated from the rhizosphere soil of pine were determined and analyzed. The effect of the VOCs on the mycelial growth of Colletotrichum gloeosporioides, the pathogen of Liriodendron chinense × tulipifera black spot, was determined by a joined-petri dish fumigation method. An in vitro leaf inoculation method was used to determine the fumigation effect of the VOCs on Liriodendron black spot. VOCs with antifungal activity were collected by headspace solid-phase microextraction (SPME), and their components were analyzed by gas chromatography-mass spectrometry (GC-MS). The results showed that the VOCs secreted by JZ-GX1 inhibited the mycelial growth of the tested pathogen. The VOCs destroyed the morphology of the mycelium, significantly increased the permeability of the cell membrane and downregulated the expression of pathogenicity-related genes during mycelial infection, thus inhibiting the expansion of anthracnose disease spots in leaves. In the volatile compound profile, 3-methyl-1-butanol and 2-phenylethyl methyl ether significantly inhibited the mycelial growth and spore germination of C. gloeosporioides. This work provides a new strategy for the research and application of microorganisms and bioactive compounds to control plant anthracnose.

The Role of Glyceraldehyde-3-Phosphate Dehydrogenases in NADPH Supply in the Oleaginous Filamentous Fungus Mortierella alpina

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a highly conserved enzyme within the glycolytic pathway. GAPDH catalyzes the transformation of glyceraldehyde 3-phosphate to glycerate-1, 3-biphosphate, a process accompanied by the production of NADH. Its role in the NADPH production system of the oleaginous filamentous fungus Mortierella alpina was explored. Two copies of genes encoding GAPDH were characterized, then endogenously overexpressed and silenced through Agrobacterium tumefaciens-mediated transformation methods. The results showed that the lipid content of the overexpression strain, MA-GAPDH1, increased by around 13%. RNA interference of GAPDH1 and GAPDH2 (MA-RGAPDH1 and MA-RGAPDH2) greatly reduced the biomass of the fungus. The lipid content of MA-RGAPDH2 was found to be about 23% higher than that of the control. Both of the lipid-increasing transformants showed a higher NADPH/NADP ratio. Analysis of metabolite and enzyme expression levels revealed that the increased lipid content of MA-GAPDH1 was due to enhanced flux of glyceraldehyde-3-phosphate to glycerate-1, 3-biphosphate. MA-RGAPDH2 was found to strengthen the metabolic flux of dihydroxyacetone phosphate to glycerol-3-phosphate. Thus, GAPDH1 contributes to NADPH supply and lipid accumulation in M. alpina, and has a distinct role from GAPDH2.

Etiology of Cyclocarya paliurus Anthracnose in Jiangsu Province, China

Cyclocarya paliurus is an extremely valuable and multifunctional tree species whose leaves have traditionally been used in used in medicine or as a medicinal tea in China. In recent years, anthracnose has been frequently observed on young leaves of C. paliurus in several nurseries located in Jiangsu Province, resulting in great yield and quality losses. To date, no information is available about the prevalence of C. paliurus anthracnose in China. The main purpose of the present study was to characterize the etiology of C. paliurus anthracnose. Phylogenetic analysis of the eight-loci concatenated dataset revealed that all 44 single-spore Colletotrichum isolates belonged to three species in the Colletotrichum gloeosporioides species complex, namely, Colletotrichum aenigma, Colletotrichum fructicola, and C. gloeosporioides sensu stricto. Phenotypic features, including the colony appearance and the morphology of conidia, appressoria, and ascospores, were consistent with the phylogenetic grouping. Virulence tests validated that the three Colletotrichum species could cause typical symptoms of anthracnose on C. paliurus leaves, similar to those observed in the field. The optimum mycelial growth temperature ranged from 25 to 30°C for all representative isolates, while C. gloeosporioides s. s. isolates exhibited greater tolerance to high temperature (40°C). Fungicide sensitivity assays indicated that all three Colletotrichum species were sensitive to tetramycin, which may be a potential alternative for the management of C. paliurus anthracnose. To our knowledge, this study provides the first report of C. aenigma, C. fructicola, and C. gloeosporioides s. s. causing C. paliurus anthracnose in China as well as in the world.

A High-Quality Draft Genome Sequence of Colletotrichum gloeosporioides sensu stricto SMCG1#C, a Causal Agent of Anthracnose on Cunninghamia lanceolata in China

Colletotrichum has a broad host range and causes major yield losses of crops. The fungus Colletotrichum gloeosporioides is associated with anthracnose on Chinese fir. In this study, we present a high-quality draft genome sequence of C. gloeosporioides sensu stricto SMCG1#C, providing a reference genomic data for further research on anthracnose of Chinese fir and other hosts.