Responses ofEchinochloaSpecies and Rice (Oryza sativa)to Indigenous Pathogenic Fungi

Abstract

Six pathogenic fungal species were isolated from naturally infected Echinochloa species and evaluated as biological control agents of Echinochloa species in rice. Curvularia lunata var. aeria and Exserohilum oryzae were pathogenic to both rice and Echinochloa species and were not evaluated further. Bipolaris sacchari, Curvularia geniculata, Dactylaria dimorphospora, and Exserohilum monoceras were pathogenic only to Echinochloa species and were further compared for virulence under controlled environment conditions in the greenhouse. When provided a 24-h dew period, Exserohilum monoceras killed seedlings of all three Echinochloa species tested: E. crus-galli, E. colona, and E. glabrescens; B. sacchari resulted in 100% mortality of seedlings of E. colona and E. glabrescens; C. geniculata killed seedlings of only E. colona; and D. dimorphospora did not cause any plant death. When given a 12-h dew period, Exserohilum monoceras still killed the three Echinochloa species, whereas the other fungi did not cause plant death. Echinochloa seedlings at the one- and two-leaf stages were more susceptible to these fungi than were seedlings at the three- and four-leaf stages. B. sacchari, Exserohilum monoceras, and E. oryzae produced phytotoxins that caused 100% leaf area chlorosis and wilting of intact seedlings of the Echinochloa species placed in cell-free culture filtrates.