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Effects of Root-Wounding and Inoculum Density on Cephalosporium Stripe in Winter Wheat. L. P. Specht, Postdoctoral research associate, Department of Plant Pathology, Washington State University, Pullman 99164-6430; T. D. Murray, associate professor, Department of Plant Pathology, Washington State University, Pullman 99164-6430. Phytopathology 80:1108-1114. Accepted for publication 23 April 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-1108.

Winter wheat cultivars Stephens and Nugaines were grown in soil adjusted to pH 4.6?7.7 and ?0.01 MPa matric potential. Root-wounding, inoculum density of Cephalosporium gramineum, and soil pH each influenced the percentage of headed tillers with Cephalosporium stripe. In unwounded plants, average incidence of diseased tillers increased from 0.5 to 22.0% as inoculum density increased from 3.4 to 6.4 log10 conidia/g of soil, and from 8.0 to 17.5% as soil pH decreased from 7.6 to 4.7. With plants whose root systems were cut immediately before infesting soil with conidia, average disease incidence increased from 16.1 to 76.7% as inoculum density increased from 1.4 to 4.4 log10 conidia/g. Root wounds were important in infection; with wounding, disease incidence was high even at moderate inoculum densities, regardless of soil pH. Because disease incidence increased with decreasing soil pH in unwounded but not in root-wounded winter wheat plants (where rapid infection of exposed xylem vessels probably occurred), acid soil appears to favor Cephalosporium stripe, at least in part, by promoting increased host susceptibility to root infection, possibly as a result of greater root stress/damage in acid than in neutral or alkaline soil.

Additional keywords: host resistance.