VIEW ARTICLE

Ecology and Epidemiology

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. C. C. Mundt, Former graduate research assistant, U.S. Department of Agriculture, Agricultural Research Service, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616, Present address: Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902; K. J. Leonard, research plant pathologist, Department of Agriculture, Agricultural Research Service, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 76:895-900. Accepted for publication 18 February 1986. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1986. DOI: 10.1094/Phyto-76-895.

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, 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 plots. 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.