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Aggressiveness of Pyrenophora tritici-repentis Isolated from Grass and Barley Hosts. 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. 76:783-789. Accepted for publication 31 January 1992. 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-76-0783.

Isolates from grass and barley hosts were tested for their aggressiveness on inoculated detached seedling leaves of wheat. In phase 1, isolates were determined to be pathogenic on wheat, and differences among isolates were detected. In phase 2, isolates that caused a high or low level of symptom expression were identified. In phase 3, differences in aggressiveness were identified when grass and barley isolates causing high and low levels of symptom expression were compared for symptom production and differentiated. In phase 4, differences in aggressiveness for grass and barley isolates were confirmed and were found to be similar to those reported for wheat and smooth bromegrass isolates from previous studies. Isolate effects were significant in all studies. Thus, as potential hosts of P. tritici-repentis, grass or barley can potentially host isolates that differ in aggressiveness. Cultivar effects were significant in most studies (25 of 27), indicating that differences in resistance among cultivars can be detected with grass or barley isolates. Cultivar isolate interactions were nonsignificant in most studies (21 of 27), indicating a general lack of specific interaction between isolates and wheat cultivars. The possibility of physiological specialization was considered to be low with the isolates under study, and isolates were considered to differ in aggressiveness. In glasshouse inoculations of wheat seedlings with grass and barley isolates, the high aggressive isolates incited more symptoms than the low aggressive isolates, confirming differences in aggressiveness determined by detached leaf inoculations.

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