Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/1998
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, wheat breeders need to know which resistance genes will be effective. Collections of the wheat leaf rust fungus were made throughout the United States from 1993-19 1993-1995, 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 from local overwintering sources. Nationally, losses in yield from leaf rust in winter wheat were estimated at 4.8% in 1992, 4.8% in 1993, 0.7% in 1994 an 2.4% in 1995. 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 1993, 1994 and 1995. Sixty-two virulence/avirulence phenotypes on 14 host lines that are near-isogenic for leaf rust resistance were found among 681 single euredinial isolates in 1993, 42 phenotypes were found among 683 isolates in 1994, and 51 among 701 isolates in 1995. 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. Collections from nurseries were significantly more diverse than collections from fields in the Northeast, Northwest, and northern Plains but not in other areas of the U.S.