EFFECT OF SEXUAL RECOMBINATION IN 2 POPULATIONS OF THE WHEAT LEAF RUST FUNGUS PUCCINIA-RECONDITA

The effect of sexual recombination on diversity and distribution of virulences was measured in two random mating populations of Puccinia recondita f.sp. tritici from the eastern and prairie regions of Canada. Teliospores derived from composite uredinial collections from both populations were germinated over leaves of Thalictrum speciosissimum, and aeciospore isolates were derived from fertilized pycnia. Virulence phenotypes of aeciospore isolates in both populations were determined on isogenic host differential sets. Comparisons of phenotypic diversity, distribution of specific virulences, and differences in specific virulences among phenotypes were made between the progenitor uredinial populations and the derived aecial populations. Sexual recombination had a greater effect of increasing diversity and randomly distributing virulences in the eastern aecial population than in the prairie aecial population. The differences in the two aecial populations most likely resulted from linkage disequilibrium between virulences generated by host selection in the prairie uredinial population, compared with the lower initial level of disequilibrium in the relatively unselected eastern uredinial population.