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Interactions Between Cochliobolus sativus and Pyrenophora tritici-repentis on Wheat Leaves. W. C. da Luz, Former graduate student, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Current address: Research plant pathologist at Centro Nacional de Pesquisa de Trigo, Passo Fundo RS, 99100, Brazil; G. C. Bergstrom, Assistant professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 77:1355-1360. Accepted for publication 2 April 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-1355.

Following mixed inoculation with Cochliobolus sativus, incitant of spot blotch, and Pyrenophora tritici-repentis, incitant of tan spot, wheat leaves developed less necrosis than the average produced by the two pathogens alone at inoculum concentrations equal to those used in the mixed inocula. Spot blotch predominated over tan spot following simultaneous inoculations or sequential inoculations where P. tritici-repentis preceded C. sativus by up to 6 hr. Antagonism occurred even when inocula contained only 20% C. sativus. Inoculation with C. sativus resulted in reduced conidial germination, slowed germ tube development, and reduced appressorium formation in P. tritici-repentis. Tan spot development may be suppressed in the field where environmental conditions favor spot blotch. C. sativus or its metabolites could potentially be manipulated to produce an effective biological control for tan spot of wheat.

Additional keywords: Bipolaris sorokiniana, Drechslera tritici-repentis.