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Using Race-Specific Resistance to Manage the Evolution of Plant Pathogens¹

ABSTRACT

The life cycle of a pathogen and the epidemiology of the disease it causes determine the use that can be made of host genes for race-specific resistance. Many pathogens, such as the potato late blight fungus, complete their life cycle in a limited area and the pathogen's evolution is determined by the host cultivars grown in the area. Other pathogens, such as the wheat stem rust fungus, survive part of the year in only a small area but then spread widely from this primary center of infection. The stem rust fungus rarely overwinters north of central Texas, but during spring and summer it spreads north 2,000 miles along the "PucciniaPath". It normally does not survive the hot summer in the overwintering area. Thus, in the fall spores must be blown south to infect the young winter wheat crop. With an epidemiological pattern of this type, the evolution of pathogenicity in the fungus is determined by the host genes for resistance that are used in particular areas. The wheat crop is a patchwork of different resistance genotypes that act as a selection sieve through which only certain rust genotypes can pass. Man, by controlling the nature of the patchwork, can guide the evolution of the pathogen to achieve long-lasting control of the disease.

Key Words: Puccinia graminis tritici • cereal rusts

¹ Paper presented Aug. 18, 1971, in New York City at the annual meeting of the ASA as part of the symposium "Breeding and Management for Stable Resistance to Plant Diseases."

² Professor and Head, Crop Science Dept., University of Saskatchewan, Saskatoon, Sask.

Received for publication December 6, 1971.