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Selection of Virulence Phenotypes in a Heterogeneous, Asexual Population of Puccinia recondita f. sp. tritici. J. A. Kolmer, Research scientist, Agriculture Canada Research Station, 195 Dafoe Rd., Winnipeg, MB. Canada, R3T 2M9; Phytopathology 80:1377-1381. Accepted for publication 30 May 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-1377.

A heterogeneous population of Puccinia recondita f. sp. tritici was cultured for eight asexual uredinial generations on adult plants of the wheat lines Thatcher, Thatcher isogenic line Lr13, TCLr16, and Chris (Lr13 + Lr34). Frequencies of virulence phenotypes changed significantly from the initial generation in the populations cultured on TCLr13, TCLr16, and Chris. Little change was observed in frequencies of virulence phenotypes in the Thatcher population. The Chris, TCLr13, and Thatcher populations maintained the phenotypic diversity found in the initial population. The TCLr16 population was dominated by one virulence phenotype after eight generations of selection. Rogers indexes of phenotypic overlap indicated that TCLr13 and Chris selected similar populations. Urediniospore production tests indicated that the TCLr16, and Chris populations had become specifically adapted to their respective hosts relative to the initial population. The population cultured on TCLr13 showed little adaptation to TCLr13, and the population cultured on Thatcher showed no adaptation. The changes in virulence phenotype frequencies and adaptation within the populations were most likely caused by nonrandom distribution of genetic variation for urediniospore production on the selection lines within the initial population.

Additional keywords: adult plant resistance, Triticum, virulence associations, wheat leaf rust.