Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 29, 2000
Publication Date: N/A
Interpretive Summary: Leaf rust, a potentially devastating disease of wheat, is controlled by resistant varieties grown in the United States. Many genes for leaf rust resistance are available to wheat breeders, but populations of the leaf rust fungus contain a variety of virulent races. Therefore, whet breeders need to know which resistance genes will be effective. Collections of the wheat leaf rust fungus were made throughout the United states from 1996 to 1998, as part of ongoing monitoring of leaf rust races. Each rust isolate was tested for virulence on wheat lines with 14 different genes for resistance. Increase of virulence to several specific resistance genes was noted in some parts of the United States. The distinctive racial composition of collections from some areas indicate that populations of rust in these areas are discrete, suggesting localized epidemics form local overwintering sources. Nationally, losses in yield from leaf rust in winter wheat were estimated at 0.8% in 1996, 2.9% in 1997 and 1.6% in 1998 The trends in importance of leaf rust and changes in prevalence of races in different areas of the United States will be used by wheat breeders to choose sources of resistance for new varieties and by wheat pathologists to assess the need for additional rust control measures in their states.
Technical Abstract: Isolates of Puccinia triticina 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 1996, 1997 and 1998. Virulence/avirulence phenotypes were determined on 14 host lines that are near-isogenic for leaf rust resistance. We found 31 phenotypes among 277 single uredinial isolates in 1996, 56 phenotypes amon 989 isolates in 1997, and 43 phenotypes among 989 isolates in 1998. As in previous surveys, regional race distribution patterns showed that the central United States is a single epidemiological unit distinct from the eastern United States. The distinctive racial composition of collections from the Southeast, Northeast and Ohio Valley indicate that populations of P. triticina in those areas are discrete, suggesting epidemics originate from localized overwintering sources.