RESPONSES OF ECHINOCHLOA SPECIES AND RICE (ORYZA-SATIVA) TO INDIGENOUS PATHOGENIC FUNGI

Six pathogenic fungal species were isolated from naturally infected Ec hinochloa species and evaluated as biological control agents of Echino chloa species in rice. Curvularia lunata var. aeria and Exserohilum or yzae were pathogenic to both rice and Echinochloa species and were not evaluated further. Bipolaris sacchari, Curvularia geniculata, Dactyla ria dimorphospora, and Exserohilum monoceras were pathogenic only to E chinochloa species and were further compared for virulence under contr olled environment conditions in the greenhouse. When provided a 24-h d ew period, Exserohilum monoceras killed seedlings of all three Echinoc hloa species tested: E. crus-galli, E. colona, and E. glabrescens; B. sacchari resulted in 100% mortality of seedlings of E. colona and E. g labrescens; C. geniculata killed seedlings of only E. colona; and D. d imorphospora did not cause any plant death. When given a 12-h dew peri od, Exserohilum monoceras still killed the three Echinochloa species, whereas the other fungi did not cause plant death. Echinochloa seedlin gs at the one- and two-leaf stages were more susceptible to these fung i 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 Echin ochloa species placed in cell-free culture filtrates.