Susceptibility of select U.S. winter wheat cultivars to wheat blast (Magnaporthe oryzae)
G. L. PETERSON (1), K. F. Pedley (1), W. W. Bockus (2), J. P. Stack (2), C. D. Cruz (2), B. S. Valent (2)
(1) USDA ARS NAA FDWSRU, Fort Detrick, MD, U.S.A.; (2) Kansas State University, Manhattan, KS, U.S.A.
Phytopathology 101:S141

Wheat blast, caused by a pathotype of Magnaporthe oryzae, is an emerging disease in South America. Countries reporting the disease are Brazil, Bolivia, Paraguay and Argentina. Field losses of 30 to 100% have been observed under favorable environmental conditions. The establishment potential of wheat blast in other regions of the world has not been determined, but the spread of this seed transmissible disease is likely. In anticipation of its arrival in the U.S., studies were initiated to assess U.S. wheat cultivars for disease resistance. Reported here are preliminary results of a biological safety level-3 greenhouse screening of 200 U.S. winter wheat cultivars for head blast resistance using a single Brazilian isolate (T-25). For each cultivar, 7 to 20 spikes at growth stage 50 were spray-inoculated with a M. oryzae conidia suspension at a rate of 1 × 10⁵ conidia per ml applied until run-off. Individual spikes were enclosed in small a plastic bag to maintain high humidity for 24 h at 23–25°C. After 21 days, spikes were evaluated based in the number of infected florets per spike. Cultivars with less than 10% infection were retested. Test results showed a broad range of susceptibility. Soft red wheat cultivars ARS05-00443, GA00067-8E35 and GA011493-8E18 averaged less than 4% infection, while hard red wheats, KS0603A-57-1, Jackpot, and CO050173 averaged less that 10%. Identification of resistant germplasm will be essential for a U.S. disease recovery plan.