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Interactions of Puccinia striiformis and Mycosphaerella graminicola on Wheat. Ricardo Madariaga B., Former Graduate Student, Department of Plant Pathology, Montana State University, Bozeman 59717. A. L. Scharen, USDA, ARS, Department of Plant Pathology, Montana State University, Bozeman 59717. Plant Dis. 70:651-654. Accepted for publication 3 February 1986. 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, 1986. DOI: 10.1094/PD-70-651.

Puccinia striiformis and Mycosphaerella graminicola are frequently found attacking the same wheat leaf. The effect of one pathogen on another and the effects of interactions between pathogens on host-pathogen interactions were studied. Seedlings of four spring wheat cultivars were inoculated at different times with various combinations of P. striiformis and M. graminicola. The two pathogens could colonize the same leaf simultaneously, and the area diseased was similar or smaller than the area affected by each organism separately. A smaller amount of leaf tissue was colonized by P. striiformis when M. graminicola was present. M. graminicola acted as a hypostatic parasite toward the rust. Wheat seedling leaves infected by P. striiformis remained green longer and had greater dry weight than leaves infected by both pathogens. This may have been due to the sequestering effect known to be characteristic of rusts. It is possible that M. graminicola interfered with the redirection of translocation of assimilates that is a common effect of rusts.

Keyword(s): Septoria tritici, stripe rust.