Development of Crown Rust Epidemics in Genetically Diverse Oat Populations: Effect of Genotype Unit Area

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Abstract
Crown rust of oats was used as a model to test the effect of genotype unit area (the ground area occupied by an individual, independent unit of the host population that is genetically homogeneous) on the disease-reducing effectiveness of genetically diverse host populations. Multilines with differing genotype unit areas were obtained by arranging near-isogenic oat lines (isolines) into units of the same genotype and randomly positioning these units within plots, while keeping the proportions of isolines constant among multiline treatments. In 1980, mixtures of 4 isolines were used and disease progression was quantified by trapping uredospores over the plots with Rotorod spore samplers. In 1981, mixtures of an immune and a susceptible isoline were used and rust severity was estimated on the susceptible isoline at one point in time. Increasing genotype unit area from 0.003 to 0.84 and 0.58 m2 in 1980 and 1981, respectively, had no significant effect on the efficacy of the multilines relative to a pure-line susceptible check.