Echinochloa species are major weeds in rice-cropping systems and are among the most noxious weeds in the world. Throughout the world, Echinochloa oryzicola Vasing, (late watergrass) is one of the most important and serious weed species of this genus. In September 2010, punctiform, purplish dark brown leaf spots were observed on leaves and sheaths of Echinochloa oryzicola in a rice field in Terme, Turkey (41°13.412′N, 36°56.248′E). Individual lesions ranged from 1 to 3 mm in diameter. Infected leaf and sheaths were surface disinfected for 1 min in 1% NaOCl, plated on potato dextrose agar (PDA), and incubated at 25°C. Colonies of pure cultures on PDA turned to dark green colonies with increasing age. Conidia were 87 to 147 (120) × 15 to 21 (19) μm (n = 50), 6 to 10 pseudoseptate, straight or slightly curved, fusiform, tapering gradually toward the base, pale-to-dark straw colored, smooth, with a small protruding plenum-type hilum. The fungus was identified as Exserohilum monoceras (Drechsler) Leonard & Suggs based on its micromorphology and cultural features (1,2). Conidia were harvested from 3-week-old cultures grown on PDA by brushing the surface of the colonies with a small paint brush, suspending the conidia in sterile distilled water and filtering through cheesecloth for pathogenicity tests. Conidia were then diluted in sterile distilled water plus 0.1% polysorbate 20 to a concentration of 1 × 106 conidia/ml. Leaves and stems of Echinochloa oryzicola at the three-leaf stage were spray inoculated with 10 ml of this aqueous suspension per plant. Three inoculated plants and three noninoculated plants were placed in a dew chamber at 18 to 22°C with continuous dew, and after 48 h, plants were moved to a greenhouse bench. Symptoms, similar to those originally observed in the field, began to appear on the leaf and sheaths approximately 10 days later and E. monoceras was reisolated, successfully completing Koch's postulates. No symptoms developed on the control plants. E. monoceras has also been reported on Echinochloa oryzicola in Japan (3). To our knowledge, this is the first report of leaf spot on Echinochloa oryzicola caused by E. monoceras in Turkey where the fungus may have potential as a biological control agent.
References: (1) M. B. Ellis. Dematiaceous Hyphomycetes. Commonwealth Mycological Institute. Kew, Surrey, England, 1971. (2) M. Sisterna and R. Bezus. Plant Dis. 85:803, 2001. (3) H. Tsukamoton et al. Ann. Phytopathol. Soc. Jpn. 64:526, 1998.