GENETIC CONTROL OF AGGRESSIVENESS IN USTILAGO HORDEI. I. NATURAL VARIABILITY AMONG PHYSIOLOGICAL RACES

Abstract

A biometrical genetic study was carried out to investigate the natural variability in aggressiveness (degree of virulence) among the 13 races of U. hordei using monosporidial cultures isolated at random to set up all possible combinations among the races. Barley plants of the variety Odessa were used as host in a completely randomized blocks experiment where aggressiveness was recorded as percentage of infected spikes in a row of 30 plants.A considerable amount of variability was detected, race No. 1 being the most and race No. 5 the least in aggressiveness. Genetic variability amounted to 51.23% of the total phenotypic variability. It was obvious that most of the genetic variability was due to additive genetic effects, suggesting no important role of dominance and epistasis. The practical application of the findings in developing resistant varieties of plants is discussed.