A Growth Chamber Comparison of Traits of Aggressiveness in Sexual and Asexual Populations ofPuccinia coronata

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Abstract
Uredial isolates of P. coronata, derived from aecia on Rhamnus cathartica in Minnesota [USA] were compared for several traits of aggressiveness with uredial isolates [from oats Avena sativa] from southern Texas where the role of the alternate host is reduced or nonexistent. Mean values of most traits differed significantly within each population. Uredial dimensions and urediospore production exhibited significantly higher mean values in the sexual population from Minnesota than in the asexual population from Texas. Uredial latent period and time to formation of telia were also significantly shorter in the sexual population. In contrast, there were no significant differences between the sexual and asexual population in the amount of genotypic or phenotypic variation, suggesting that sexual reproduction conferred no advantage to the sexual population in producing a greater range of variability for traits of aggressiveness. Confidence limits (P = 0.05) of broad-sense heritability estimates for all traits ranged 18-96% in the asexual population and 26-98% in the sexual population, but no significant difference in heritability was detected for any trait between the 2 populations.