Isozyme uniformity and virulence variation in Puccinia graminis f.sp. tritici and P. recondita f.sp. tritici in Australia

During a routine survey of pathotypes of Puccinia graminis f.sp. tritici (the wheat stem rust pathogen) and P. recondita f.sp. tritici (the wheat leaf rust pathogen) present in Australia during the 1981-82 growing season, 16 pathotypes of P. graminis tritici and 12 pathotypes of P. recondita tritici were detected in total samples of 193 and 180 isolates of the two pathogens respectively. For both pathogens the distribution of isolates amongst the different pathotypes was highly uneven. Large subsamples of these field-collected isolates (58 isolates of P. graminis tritici representing seven pathotypes and 66 of P. recondia tritici representing six pathotypes) were randomly selected and used to assess isozyme variation in extant Australian populations of these two pathogens.