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A Comparison of Sexual and Asexual Populations of Puccinia coronata for Traits of Aggressiveness in the Field¹

We tested the hypothesis that sexual reproduction produces greater genetic variation than asexual reproduction and enhances the potential for selection of isolates with higher levels of aggressiveness. Certain traits of aggressiveness were compared in two field seasons between sexually and asexually derived uredial isolates of Puccinia coronata Cda. from Minnesota and Texas, respectively. Greater variation among isolates was found in the sexual than in the asexual population for traits that measured yield loss on the cultivars, ‘Clintford’, ‘Noble’, and ‘Otee’, but not on ‘Lang’ or ‘Richland’. The lack of differences between populations for variation of the measured visual traits was due to a relatively large genotype x environment interaction. Low heritability values of resistance, as estimated by yield and seed weight indexes, in the asexual population were attributed to the strong genotype x environment interaction, whereas corresponding values in the sexual population were affected less by the interaction. Data from the sexual Minnesota population may not accurately predict the range of variation for aggressiveness in the asexual Texas population due to different selection pressures operating within the two populations. Heritability estimates suggested that any advantage of sexual reproduction to increase variation in aggressiveness over that of asexual reproduction is trait, cultivar, and environment specific.

Key Words: Crown rust • Avena sativa L. • Aggressiveness • Sexual reproduction

² Former graduate research assistant (now research associate, Dep. of Agronomy and Range Science, Univ. of California, Davis, CA 95616) and research plant pathologist, USDA-ARS, Dep. of Plant Pathology, Iowa State University, Ames, IA 50011.

Received for publication July 5, 1983.