Mung bean sprouts (Vigna radiata (L.) R. Wilczek) are a commonly consumed vegetable in Asian countries. Anthracnose lesions on mung bean sprouts (cv. You-lu-dou from Mayamar) were found in an indoor sprouting facility in Taichung County, Taiwan in May of 2009. The incidence of disease exceeded 90% in some lots. Infected hypocotyls had smooth, diamond-shaped to fusiform brown spots, which became further depressed and enlarged with age. A fungus was isolated on potato dextrose agar (PDA) from symptomatic hypocotyls after surface sterilization in 0.6% NaOCl. Fungal colonies were initially salmon to orange in color and became greenish gray on the surface within a week. Setae were not produced in acervuli that developed on PDA. Conidia in the acervuli were one-celled, cylindrical, and hyaline with an average length and width of 14.8 (7.0 to 23.7) × 4.9 (3.3 to 6.7) μm (n = 53). The internal transcribed spacer (ITS) region was amplified with primers ITS1 and ITS4 (4). The sequence was deposited in GenBank (Accession No. GQ889269). The sequence was 99% identical to that of ATCC 56816 strain of Glomerella acutata (Guerber & J. C. Correll), the teleomorph of Colletotrichum acutatum (J. H. Simmonds) over a 522-bp alignment. Thus, the mung bean pathogen was identified as C. acutatum based on morphological (1) and molecular characters. Pathogenicity of the strain was determined by inoculating mung bean seeds from I-Mei Foods Co. (imported from Australia). The seeds were disinfested in 0.6% NaOCl for 10 min, rinsed with sterile distilled water twice, and immersed in a conidial suspension (1.5 × 104 conidia/ml) of C. acutatum for 10 min. Fifteen inoculated seeds were placed on moistened paper towels, distributed into three flasks, and stored in the dark at 32°C. Symptoms similar to those observed on the original sprouts appeared 3 days later on the hypocotyls of the seedlings and all seedlings were infected by day five. Conidia of C. acutatum were produced on all lesions and colonies of C. acutatum were recovered from symptomatic tissues, fulfilling Koch's postulates. Controls (seed immersed in water) remained symptomless. The pathogenicity test was repeated with similar results. The pathogen has been recorded on mung bean sprouts in Korea (2) and on other Vigna spp. in India (3). To our knowledge, this is the first report of sprout rot of mung bean caused by C. acutatum in Taiwan.
References: (1) B. J. Dyko and J. E. M. Mordue. No. 630 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1979. (2) D. K. Kim et al. Plant Pathol. J. 19:203, 2003. (3) K. P. R. Prasanna. Seed Sci. Technol. 13:821, 1985. (4) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, New York, 1990.
