Aggressiveness of Isolates of Pyrenophora tritici-repentis Obtained from Wheat in the Northern Great Plains. J. M. Krupinsky, Research Plant Pathologist, Agriculture Research Service, U.S. Department of Agriculture, Northern Great Plains Research Laboratory, P.O. Box 459, Mandan, ND 58554-0459. . Plant Dis. 76:87-91. Accepted for publication 4 July 1991. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1992. DOI: 10.1094/PD-76-0087.

Eighty-four isolates of Pyrenophora tritici-repentis, obtained from diseased wheat leaves collected from fields in Montana, North Dakota, and South Dakota, were tested on detached seedling leaves of wheat. All isolates were pathogenic. Different levels of aggressiveness were detected among isolates when randomly compared. Isolates with apparent-high levels of aggressiveness were found to be widespread over the region, whereas isolates with apparent-low levels of aggressiveness were detected at a lesser frequency. When compared in the same study, apparent-high and apparent-low aggressive isolates were statistically separated from one another. Differences among cultivars were detected when randomly selected isolates were used or when isolates with similar or different levels of aggressiveness were used. Cultivar effects were significant in 96% (44 of 46) of the analyses of variance. In the same tests, the cultivar × isolate interactions generally were not significant. The nonsignificance of the cultivar × isolate interaction in 91% (42 of 46) of the analyses indicated a general lack of specific interaction. This lack of specific interaction was interpreted to mean that the 84 isolates of P. tritici-repentis tested have different levels of aggressiveness and are not regarded as biotypes or races with physiologic specialization.

Keyword(s): Drechslera tritici-repentis, tan spot, yellow leaf spot.