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

Abstract

Strausbaugh, C. A., and Murray, T. D. 1989. Use of epidermal cell responses to evaluate resistance of winter wheat cultivars to Pseudocercosporella herpotrichoides. Phytopathology 79:1043-1047. Epidermal cell responses (papilla formation, penetrations stopped of differentiating cultivars for resistance to P. herpotrichoides included within epidermal cells, and hypersensitivity) on the first-leaf sheath were incubation of inoculated plants at 10 C and a disease rating based on used to determine the percent successful penetrations on susceptible and fungal penetration attempts stopped by papillae or within epidermal cells resistant winter wheat seedlings inoculated with conidia of Pseudo- in both hypersensitive and nonhypersensitive cells. The coleoptile was cercosporella herpotrichoides. The greatest disease development occurred associated with infection of the first-leaf sheath and the formation of when inoculated plants were incubated in high relative humidity at 15 C elliptical lesions occurred 0.9-2.3 cm above where the leaf sheath attached and decreased at 10, 20, and 5 C, respectively. Differences among resistant to the crown. Lesions were more distinctive on resistant than susceptible and susceptible cultivars were significant at both 10 and 15 C, although cultivars, and more resistant responses occurred near the edges than at the greatest differentiation between Cappelle-Desprez (resistant) and the centers of the lesions. No significant differences in pathogenicity were VPM-1 (highly resistant) occurred at 10 C. The most reliable method found among four isolates of P. herpotrichoides tested. Strawbreaker foot rot (eyespot), caused by Pseudocercosporella resistance (23,25). Murray and Ye (25) found that the percentage herpotrichoides (Fron) Deighton, is the most widespread, chronic of penetration sites with papillae, penetrated papillae, and total disease of winter wheat (Triticum aestivum L.) in the Pacific successful penetrations in winter wheat seedlings were positively Northwest region of the United States (26). Currently, this disease correlated with field resistance of mature plants to P. is controlled with a single foliar application of a benzimidazole herpotrichoides. However, disease development must be increased fungicide in the spring. Resistant cultivars would be more desirable and environmental variation must be reduced before this seedling since they are more economical and reliable, and because the test can be used to screen individual plants. These improvements fungus has become resistant to benzimidazole fungicides in Europe may be achieved by finding the most reliable combination of (2,5). Currently, none of the widely grown commercial winter epidermal responses (papilla formation, penetrations stopped wheat cultivars available in the Pacific Northwest have adequate within epidermal cells, and hypersensitive response) for levels of resistance to P. herpotrichoides. Wheat breeders have establishing resistance and assessing the effect of temperature on been working to incorporate foot rot resistance into adapted these responses. cultivars, but the selection of resistant cultivars is a slow process Temperature, humidity, coleoptile placement, and isolates of because plants must be grown to maturity in the field over several the pathogen influence disease development (4,13,21,31,32). years (25). Several studies have documented the ranges and optimum