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Effect of Early Season Powdery Mildew on Development, Survival, and Yield Contribution of Tillers of Winter Wheat. Kathryne L. Everts, Research associate and research plant pathologist, USDA-ARS, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616, Present address: Busch Agricultural Resources, Inc., Fort Collins, CO 80524; Steven Leath, Associate professor, USDA-ARS, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 82:1273-1278. Accepted for publication 29 July 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/Phyto-82-1273.

The formation, survival, and development of primary and secondary tillers of winter wheat (Triticum aestivum) are influenced by stresses the plant encounters during its growth. Three and two cultivars of winter wheat were planted near Clayton, North Carolina, in 1989 and 1990, respectively. Levels of powdery mildew (Blumeria graminis f. sp. tritici) were established by triadimenol seed treatment and presence or absence of rows of susceptible wheat inoculated with powdery mildew. Presence of primary and secondary tillers was determined four times during the growing season, and the contribution of each tiller to yield was assessed at harvest. There were positive correlations between the presence of some tillers and the amount of powdery mildew previously present in a plot both years of the study. In the 19891990 and 19901991 seasons, there was a delay in tiller initiation where seed had been treated with triadimenol. However, tillers of plants treated with triadimenol were more likely to survive to harvest and produce heads. Yield increased on all cultivars in both years when wheat was grown from triadimenol-treated seeds and decreased when plots were bordered by rows of wheat susceptible to powdery mildew. Increased yields were associated with reduced tiller initiation and increased survival of primary and secondary tillers. Kernel weight in 19891990 and kernel number in 19901991 also contributed to increased yields.