YIELD LOSS IN 2 SPRING OAT CULTIVARS DUE TO PUCCINIA-CORONATA F SP AVENAE IN THE PRESENCE OR ABSENCE OF BARLEY YELLOW DWARF VIRUS

Individual studies were done to estimate yield loss due to Puccinia co ronata f. sp. avenae (crown rust) in the presence or absence of barley yellow dwarf virus (BYDV-PAV-IL) for two spring oat cultivars at two locations. Crown rust disease severity was assessed several times and related to yield and yield components. Linear critical point regressio n models were developed with analysis of covariance. Yield loss for ea ch percent increase in crown rust severity (modified Cobb scale A) was 56.7 kg/ha for cv. Noble and 46.0 kg/ha for cv. Ogre. Test weight dec rease for each percent increase in crown rust severity was 1.2 kg/m(3) for Noble and 1.1 kg/m(3) for Ogle. Ogle exhibited tolerance to yield loss from crown rust. Yield loss, due to each percent increase in cro wn rust severity in BYDV-infected plots, was 19.2 kg/ha for Noble and 28.7 kg/ha for Ogle. Test weight decrease, for each percent increase i n crown rust disease severity, was not different from zero (P less tha n or equal to 0.05) for Noble and 0.7 kg/m(3) for Ogle. Noble exhibite d tolerance to yield loss from crown rust in BYDV-infected plots. The effect of BYDV on yield and reduction in test weight due to crown rust was not additive.