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Effect of Sexual and Asexual Reproduction on Race Abundance in Cereal Rust Fungus Populations. J. V. Groth, Associate professor, Department of Plant Pathology, Cereal Rust Laboratory, Agricultural Research, U.S. Department of Agriculture, University of Minnesota, St. Paul 55108; A. P. Roelfs, research plant pathologist, Cereal Rust Laboratory, Agricultural Research, U.S. Department of Agriculture, University of Minnesota, St. Paul 55108. Phytopathology 72:1503-1507. Accepted for publication 18 May 1982. 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, 1982.. DOI: 10.1094/Phyto-72-1503.

Several populations of cereal rust fungi that differed in the amount of sexual (= Type 1 where sexual reproduction occurred annually in a portion of the population) and asexual (= Type 2 where reproduction is primarily or wholly asexual) reproduction were compared for number of races and evenness of race frequency distribution. In all but one of eight cases, Type 1 populations had more races in a (visually) more even distribution than did comparable Type 2 populations. Simpsonís and Shannon-Wiener indexes of diversity were used at an intraspecific level to estimate these differences. For all populations, the mean Simpsonís indexes were 0.934 and 0.798 for the Type 1 vs Type 2 populations, respectively, and the mean Shannon-Wiener indexes were 2.76 and 2.10, respectively, which is a significant difference according to a paired t-test. Valid comparisons of two types of populations require that the same differential set be used on both since both virulence frequency and virulence associations, which determine the ability of differential cultivars to detect races, will affect the absolute size of diversity indexes.

Additional keywords: Simpsonís index of diversity, Shannon-Wiener index, gene-for-gene, Puccinia graminis f. sp. tritici, Puccinia coronata, Puccinia recondita, genetic variation.