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Influence of Number of Host Genotype Units on the Effectiveness of Host Mixtures for Disease Control: A Modeling Approach. C. C. Mundt, Assistant professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902; L. S. Brophy, Research assistant, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902. Phytopathology 78:1087-1094. Accepted for publication 14 March 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-1087.

Analytical and simulation models were used to study the influence of the number of host genotype units (individual, independent units of host tissue that are genetically homogeneous) on the development of epidemics in pure and mixed (diverse) stands of crops. Analytical models indicated that the alloinfection/autoinfection ratio and, therefore, disease control derived from genetic diversification is greater for populations with a large number of host genotype units than for populations with a smaller number of host genotype units. For computer simulations of wheat stem rust over large geographic areas, the effectiveness of interfield diversification for disease control increased with increasing number of fields planted to wheat. The absolute severity of disease, however, increased for both diversified and nondiversified regions when the number of fields was increased. Simulation studies of oat crown rust for small plots showed that the number of host genotype units in a population is a more important determinant of the effectiveness of mixtures for disease control than is host genotype unit area (the ground area occupied by a host genotype unit). Results suggest that intraspecific or interspecific mixtures of large plants and the culture of alternating rows, swaths, or fields of different host genotypes may provide greater disease control than previously anticipated.

Additional keywords: Avena sativa, cultivar mixtures, epidemiology, genetic diversity, multilines, oats, Puccinia coronata, Puccinia graminis, Triticum aestivum.