Inheritance of Resistance of Cowpea to Phytophthora vignae in Whole Plants, Cuttings and Stem Callus Cultures

Abstract

The inheritance of resistance of cowpea to Phytophthora vignae race 2 has been examined in seedlings from F₁, F₂ and backcross generations from crosses between a susceptible cultivar, cv. Poona, and a near-isogenic resistant cultivar, cv. Caloona. Resistance is dominant and controlled by a single gene (gene complex). A non-subjective method, based on comparison of the lengths of lesions produced on hybrid and parental seedlings after inoculation of cut epicotyls, was used to classify hybrid plants as resistant and susceptible. This method takes into account the variation in responses to infection between batches of plants assayed on different days. Two other criteria were used to indicate resistance: the presence of reddening responses, 3 days post-inoculation; and the ability of plants to recover 35 days after inoculation of cut epicotyls. Resistance is also expressed in excised leaves of rooted cuttings, and in stem callus derived from cv. Caloona and F₁ plants.