VIRULENCE AND DIVERSITY OF PUCCINIA-RECONDITA F-SP TRITICI IN THE UNITED-STATES IN 1991

Isolates of Puccinia recondita f. sp. tritici were obtained from wheat leaf collections made by cooperators throughout the United States and from cereal rust field surveys of the Great Plains, Ohio Valley, and Gulf Coast states in 1991. Fifty-five virulence/avirulence phenotypes were found among 647 single uredinial isolates on 14 host lines that a re isogenic for leaf rust resistance. The frequencies of virulence to lines with Lr24 and Lr26 during 1991 were greater than in previous yea rs. Regional race distribution patterns again suggested that the centr al United States is a single epidemiological unit distinct from the ea stern United States. The distinctive racial composition of collections from the Southeast, Northeast, and Ohio Valley indicate that populati ons of P. r. tritici in those areas are discrete, suggesting epidemics originate from localized overwintering sources.