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Race-Nonspecific Resistance in Bean Cultivars to Races of Uromyces appendiculatus var. appendiculatus and its Correlation with Leaf Epidermal Characteristics. Meher Shaik, Former graduate student, Botany Department, University of the West Indies, Mona, Kingston 7, Jamaica, Present address: Department of Plant Pathology, University of Nebraska, Lincoln 68583-0722; Phytopathology 75:478-481. Accepted for publication 16 November 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-478.

Race-nonspecific resistance of beans (Phaseolus vulgaris) to Uromyces appendiculatus var. appendiculatus was assessed as the number of pustules (uredosori) that developed. Five cultivars (Jamaica Red, 27R, Round Red, Miss Kelly, and Portland Red) were inoculated with three Jamaican races (J4, J10, and J15) of U. appendiculatus. The cultivars differed significantly in the number of pustules per square centimeter of leaf, regardless of the race or leaf position inoculated. In general, the order of cultivars from most resistant to least resistant was Jamaica Red, 27R, Round Red, Miss Kelly, and Portland Red. Mean number of pustules per square centimeter was positively correlated with mean stomatal density on the adaxial leaf surface and negatively correlated with mean hair density on both leaf surfaces. However, a number of additional factors are probably involved in the apparent relationship between epidermal characteristics and the development of fewer pustules. The feature of race-nonspecific resistance reported here appears to be independent of the race-specific resistance present in the cultivars studied. Jamaica Red, which developed fewest pustules, showed race-specific resistance to none of the Jamaican races tested. Other components of resistance, such as development of smaller or more sparsely sporulating pustules or longer latent periods, were not exhibited by cultivars that developed fewer pustules per unit leaf area.

Additional keywords: horizontal resistance, vertical resistance.