Trichosanthes kirilowii Maxim., a species within the gourd family, is cultivated in China for its edible seeds and medicinal roots. Since 2000, heavy losses due to fruit rot have been caused by a new disease with typical anthracnose symptoms, i.e., water-soaked, dark brown-to-black, sunken lesions. Signs of the suspected pathogen were usually seen on near-mature fruits and were especially evident after abundant rainfall. The lesions contained numerous black acervuli with black setae that produced abundant, salmon-colored spore masses under high relative humidity. Dark lesions on leaves and stems could also be found in the field that sometimes led to stem girdling and wilting. Conidia produced in acervuli were 14 to 20 × 3 to 6 μm, straight, cylindrical, hyaline, aseptate, with both ends rounded. Conidiophores were 13 to 22 × 4 to 6 μm, aseptate, and cylindrical, while the setae, usually with three to five septa, measured 60 to 86 × 5 to 6 μm. The pathogen was initially identified as Colletotrichum gloeosporioides on the basis of the morphology (2). In culture, the fungus produced a gray-to-black colony with whitish aerial mycelium on potato dextrose agar (PDA) medium. Pathogenicity was tested by inoculating the equator of 10 fruits of T. kirilowii with a 5-day-old mycelia plug from a single-spore colony (0.5 cm in diameter); fruits inoculated with the plugs of PDA medium served as the control. Inoculated fruits were covered with plastic for 24 h to maintain high relative humidity. After 4 days, 100% of the inoculated fruits showed symptoms identical to those observed on T. kirilowii fruit affected in the field, while all fruits inoculated with PDA medium remained free of symptoms. Reisolation of the fungus from fruit lesions confirmed that the causal agent was C. gloeosporioides. To confirm the pathogen to species, the C. gloeosporioides-specific primers CgInt/ITS4 and C. acutatum-specific primers CaInt2/ITS4 (1) were used to amplify the sequence of internal transcribed spacer regions. A fragment of approximately 500 bp was only amplified with primers CgInt/ITS4 and the sequence (GenBank Accession No. AM491334) was 98 to 100% matched to the sequences of several C. gloeosporioides isolates (e.g., GenBank Accession Nos. AJ301919, AB255249, AJ301908), whereas the sequence shares 86 and 91% identity to that of C. orbiculare (GenBank Accession No. AB042308) and C. acutatum (GenBank Accession No. AJ749675), respectively. Thus, we concluded that C. gloeosporioides is the causal agent of anthracnose fruit rot of T. kirilowii. To our knowledge, this is the first report of C. gloeosporioides infecting T. kirilowii.
References: (1) A. E. Brown et al. Phytopathology 86:523, 1996. (2) B. C. Sutton. The Coelomycetes. CAB International Publishing, New York, 1980.
