Use of Epidermal Cell Responses to Evaluate Resistance of Winter Wheat Cultivars toPseudocercosporella herpotrichoides

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Abstract
Epidermal cell responses (papilla formation, penetrations stopped within epidermal cells, and hypersensitivity) on the first-leaf sheath were used to determine the percent successful penetrations on susceptible and resistant winter wheat seedlings inoculated with conidia of Pseudocercosporella herpotrichoides. The greatest disease development occurred when inoculated plants were incubated in high relative humidity at 15 C and decreased at 10, 20, and 5 C, respectively. Differences among resistant and susceptible cultivars were significant at both 10 and 15 C, although the greatest differentiation between Cappelle-Desprez (resistant) and VPM-1 (highly resistant) occurred at 10 C. The most reliable method of differentiating cultivars for resistance to P. herpotrichoides included incubation of inoculated plants at 10 C and a disease rating based on fungal penetration attempts stopped by papillae or within epidermal cells in both hypersensitive and nonhypersensitive cells. The coleoptile was associated with infection of the first-leaf sheath and the formation of elliptical lesions occurred 0.9-2.3 cm above where the leaf sheath attached to the crown. Lesions were more distinctive on resistant than susceptible cultivars, and more resistant responses occurred near the edges than at the centers of the lesions. No significant differences in pathogenicity were found among four isolates of P. herpotrichoides tested.