Coelomycete systematics with special reference to Colletotrichum

Colletotrichum siamense, a Novel Causal Agent of Viburnum odoratissimum Leaf Blotch and Its Sensitivity to Fungicides

Viburnum odoratissimum Ker-Gawl is native to Asia and is usually used as a garden ornamental. In September 2022, a leaf blotch on V. odoratissimum was observed in Nanjing, Jiangsu, China. The disease causes the leaves of the plants to curl and dry up and defoliate early. It not only seriously affects the growth of the plants but also greatly reduces the ornamental value. The pathogenic fungus was isolated from the diseased leaves, and the fungus was identified to be Colletotrichum siamense based on morphological features and multilocus phylogenetic analyses of the internal transcribed spacer (ITS) region, actin (ACT), calmodulin (CAL), beta-tubulin 2 (TUB2), chitin synthase (CHS-1), Apn2-Mat1-2 intergenic spacer and partial mating type (ApMat), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes. Pathogenicity tests were performed by inoculating healthy leaves with conidia. C. siamense can grow at 15-35 °C, with an optimal growth temperature at 25-30 °C. The results of sensitivity to nine fungicides showed that C. siamense was the most sensitive to prochloraz in the concentration range of 0.01 μg/mL to 100 μg/mL. Therefore, spraying prochloraz before the optimum growth temperature of pathogenic fungus can achieve effective control. It provided useful information for future studies on the prevention and treatment strategies of C. siamense. This is the first report of leaf blotch caused by C. siamense on V. odoratissimum in China and worldwide.

New species of Colletotrichum from wild Poaceae and Cyperaceae plants in Iran

Twenty-two Colletotrichum strains were isolated from anthracnose symptoms or leaf spots on leaves of various wild Poaceae and Cyperaceae plants collected in three provinces of Iran and tentatively identified as belonging to the Graminicola species complex based on morphology. All strains were studied via a polyphasic approach combining colony characteristics, morphology and phylogeny inferred from multi-locus sequences, including the nuc rDNA ITS1-5.8S-ITS2 (ITS), partial sequences of the β-tubulin (tub2), actin (act), manganese superoxide dismutase 2 (sod2), DNA lyase 2 (apn2) genes, a 200-bp intron of the glyceraldehyde-3-phosphate dehydrogenase (gapdh), and the intergenic spacer between the apn2 gene and the mat1 idiomorph (apn2/mat1). Six species were distinguished, including three new species, namely C. caspicum, C. persicum, and C. sacchari, and three previously described species, C. cereale, C. nicholsonii and C. sublineola. Comprehensive morphological descriptions and illustrations are provided for all species. Furthermore, this study provided new insights into the distribution and host range of known species.

Characterization, Virulence, Epidemiology, and Management of Anthracnose in Celery

Leaf curling and petiole twisting of celery (Apium graveolens) were observed in several commercial fields in five Michigan counties in 2010 through 2012, causing significant crop damage and loss. Prior to this time, the pathogen Colletotrichum acutatum species complex had not been previously associated with celery in Michigan. In this study, the pathogen's genotype and phenotype were characterized, the influence of environmental conditions determined, and fungicides tested. Pathogen identification was based on conidial morphology and molecular identification using species-specific primers. Intersimple-sequence repeat (ISSR) banding patterns were similar between C. acutatum isolates from celery (n = 51) and blueberry (n = 1) but different from C. dematium and C. gloeosporioides. Four ISSR primers resulted in 4% polymorphism when tested on isolates from celery. Pathogenicity and virulence of C. acutatum sensu lato isolated from celery (n = 81), tomato (n = 2), and blueberry (n = 1) were evaluated in greenhouse experiments, which revealed differences in virulence among isolates but no significant differences specific to collection year, county, or field. In dew chambers and growth chambers, high temperatures (≥25°C) or long leaf wetness duration (>24 h) increased disease incidence. Twelve fungicides were tested in field studies over two growing seasons to determine their efficacy against celery anthracnose. The fungicides azoxystrobin, pyraclostrobin, mancozeb, and chlorothalonil reduced disease by 27 to 50% compared with the untreated control when disease pressure was moderate.

Multiplex Real-time PCR Detection and Differentiation of Colletotrichum Species Infecting Soybean

Colletotrichum species are fungal plant pathogens of worldwide significance. Colletotrichum species were isolated from soybean with anthracnose symptoms in five states in the United States from 2009 to 2013. Among 240 isolates collected, four Colletotrichum species were initially identified by morphological and sequence analysis, including C. chlorophyti, C. incanum, C. truncatum, and Colletotrichum sp. (henceforth Glomerella glycines, the name of its sexual state). To increase diagnostic efficiency and accuracy, real-time multiplex PCR assays based on a double-stranded DNA-binding dye coupled with dissociation curve analysis were designed, using a region of the cytochrome c oxidase subunit 1 (cox1) gene to discern these four Colletotrichum species. Two sets of duplex, real-time PCR assays were established and species differentiation was based upon amplicon melting point temperatures (T_m) in the dissociation curve analysis. The Set 1 duplex assay distinguished C. chlorophyti and G. glycines, and the Set 2 duplex assay distinguished C. incanum and C. truncatum. Successful detection was achieved with as little as 1 pg DNA. The assays were especially useful for differentiating C. chlorophyti, C. incanum, and C. truncatum, which have similar morphological features. Colletotrichum gloeosporioides, another pathogen associated with soybean anthracnose, was not resolved from G. glycines by the melting curve analysis. The two duplex real-time PCR assays were used to screen more than 200 purified Colletotrichum isolates, showing that they were rapid and effective methods to detect and differentiate Colletotrichum species infecting soybean.

Colletotrichum incanum sp. nov., a curved-conidial species causing soybean anthracnose in USA

Soybean anthracnose is caused by a number of species of Colletotrichum that as a group represent an important disease that results in significant economic losses. In the current study, Colletotrichum species were isolated from soybean petioles and stems with anthracnose symptoms from soybean fields in Illinois. Multigene sequence phylogenic analysis, combining rDNA internal transcribed spacer, actin, β-tubulin, glyceraldehyde-3-phosphate dehydrogenase and histone H3 gene regions, revealed a group of isolates collected in this study to be distinct from other established Colletotrichum species. This new group was phylogenetically closer to C. liriopes, C. tofieldiae and C. verruculosum than to C. truncatum, another species with curved conidia commonly found on soybean. A representative isolate from this new group was used to examine its morphology, cultural characteristics and pathogenicity to soybean; it was found to differ from C. truncatum in colony culture characteristics and sizes of conidia and appressoria. As a result of the molecular phylogenetic, morphological and pathogenicity analyses, we named this species Colletotrichum incanum. Of the 84 Colletotrichum isolates collected from soybean petioles, 40 were C. incanum, indicating that this species may commonly occur.