Race-Nonspecific Resistance in Bean Cultivars to Races ofUromyces appendiculatusvar.appendiculatusand its Correlation with Leaf Epidermal Characteristics

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Abstract
Race-nonspecific resistance of beans (P. vulgaris) to U. appendiculatus var. appendiculatus [rust] 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 3 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. 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.

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