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Effect of Wetting-Period Duration on Ascocarp Suppression by Selected Antagonistic Fungi in Wheat Straw Infested with Pyrenophora tritici-repentis. Wei Zhang, Graduate research assistant, Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506-5502; William F. Pfender, associate professor, Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506-5502. Phytopathology 83:1288-1293. Accepted for publication 2 September 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-1288.

Wheat straw axenically or naturally infested with Pyrenophora tritici-repentis was inoculated with one of several antagonistic fungi and exposed to various treatments of alternate wetting and drying, and ascocarp production by P. tritici-repentis on straw was measured. Wetting treatments were repeated wet periods of 6, 12, 24, or 48 h separated by drying periods. In the absence of suppressive fungi, ascocarp formation by P. tritici-repentis was observed in both axenically colonized straw and naturally infested field straw in all wetting treatments, and the effect of wetting duration on ascocarp formation was not obvious. Suppression of ascocarp formation in both field and axenic straw by selected antagonistic fungi was affected by the duration of intermittent wetting. In field straw, the number of large ascocarps produced by P. tritici-repentis was significantly reduced by Laetisaria arvalis, Sterile II, and Limonomyces roseipellis under 24- and 48-h wetting periods but not under 6- and 12-h wetting periods compared to the uninoculated control. Compared to field straw, suppression of ascocarp formation in axenic straw by the test fungi was much less. L. arvalis reduced ascocarp formation in the 24- and 12-h wetting treatments compared to the uninoculated control. Under the 48-h wetting treatment, Sterile II inhibited ascocarp formation in one experiment but increased ascocarp formation in the other. Limonomyces roseipellis did not inhibit ascocarp formation in axenic straw. Thus, ascocarp suppression in wheat straw by selected antagonistic fungi occurred only under relatively long (>12 h) wetting periods.