DIVERSITY OF VIRULENCE WITHIN AND AMONG POPULATIONS OF PUCCINIA-RECONDITA F SP TRITICI IN DIFFERENT AREAS OF THE UNITED-STATES

Data from surveys of pathogenic races of Puccinia recondita f. sp. tritici from 1988 to 1990 were analyzed to compare phenotypic diversity within and among pathogen populations in eight areas of the United States. Collections from nurseries were significantly more diverse than those from commercial fields in five of seven areas. Populations from the southern, central, and northern Great Plains were phenotypically similar. The population from California and other southwestern states was distinctly different from populations from all other areas. Leaf rust pathogen populations in the Pacific Northwest were no more similar to those of the Great Plains than to populations in areas east of the Mississippi River. The midwestern, northeastern, and southeastern populations were sufficiently distinct to indicate local sources of primary inoculum with limited exchange among those areas.