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Reduction in Pycnidial Coverage After Inoculation of Wheat with Mixtures of Isolates of Septoria tritici. Noga Zelikovitch and Z. Eyal, Department of Botany, The George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 69978, Israel. Plant Dis. 75:907-910. Accepted for publication 29 January 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0907.

Inoculation of wheat seedlings with certain combinations of isolates of Septoria tritici resulted in marked reductions in pycnidial coverage of leaves compared with plants inoculated separately with individual components of the mixture. The effect was greater when the isolates were grown together than when grown separately and mixed before inoculation. The suppression of pycnidial formation did not depend on the ratio of the isolates in the mixtures. The addition of a culture filtrate from one isolate to the conidial preparation of another isolate resulted in marked symptom suppression. In conidial preparations where the growth medium was decanted and the spores were resuspended in fresh medium, marked reductions in pycnidial coverages were observed on all cultivars. These results suggest that S. tritici may produce substances that regulate the expression of symptoms on wheat leaves inoculated with isolate mixtures. Challenge inoculations of Kavkaz winter wheat with an isolate several days after the first inoculation with a different isolate also resulted in significant reductions in pycnidial coverage. It is possible that a resistant host response is triggered by the first inoculation.

Additional keywords: Septoria tritici blotch, Triticum aestivum