A biometrical-genetical study of the effects and interactions of the parasite, the host and the environment on growth rate and aggressiveness of Ustilage hordei (Pers.) Lagerh

From two teliospores of ustilago hordei (Pers.) Lagerh (the fungus causing the covered smut disease of barley) the eight monokaryons and the sixteen possible dikaryons derived rom the monokaryotic matings, were used in a biometrical genetic study. Evaluations were made of the relative roles of the genotype, environment and genotype-environment interactions in determining growth rate of the monokaryons and aggressiveness of the dikaryons (parasites). The genetics of host-parasite relationships was also examined using different barley cultivars as hosts. -- The genotype, the environment, and the interaction of the two were found to contribute significantly to the control of variability in growth rate of the monokaryons. Variability in degree of infection of the dikaryons was controlled by the environment, the genotype of the parasite (aggressiveness), and the genotype of the host (tolerance). There were no significant effects from parasite-environment interactions or from host-parasite interactions. -- The aggressiveness of the dikaryons (parasites) and the growth rates of the parental monokaryons were positively correlated, suggesting that both characters may be under the control of a common gene system. It was also demonstrated that faster growth rate in the monokaryons was accompanied by an increased sensitivity to environmental change. -- A general biometrical-genetical model was developed to describe the relationships and interactions within a host-parasite-environment system