Effect of Host Genotype Unit Area on Development of Focal Epidemics of Bean Rust and Common Maize Rust in Mixtures of Resistant and Susceptible Plants

Publisher Website
Google Scholar
Abstract
We studied the effect of host genotype unit area (ground area occupied by an independent, genetically homogeneous unit of a host population) on the effectiveness of host mixtures for controlling focal epidemics of common maize rust and bean rust. For both crops, [Zea mays, Phaseolus vulgaris], mixtures of resistant and susceptible plants with four genotype unit areas were established by altering the spatial arrangement of host genotypes within plots. With maize, genotype unit area for a mixture of 1:3 susceptible/resistant plants was increased from 0.21 to 1.88 m2. By the end of the epidemics, there were fewer than half as many pustules on susceptible plants in the mixtures as on plants in the pure-line susceptible plots. However, there was little difference in the amount of disease in the mixtures with the four genotype unit areas. With beans, genotype unit area was increased from 0.023 to 0.84 m2 in mixtures of either 1:1 or 1:3 susceptible/resistant plants over 3 yr (1982-1984). There was always less disease on susceptible plants in mixtures with the smaller genotype unit areas than in the pure-line susceptible plants. In all 3 yr, the effectiveness of the mixture declined as the genotype unit area increased. However, the quantitative relationship between mixture efficacy and genotype unit area varied among years.