SELECTIVE INFLUENCE OF WHEAT CULTIVARS ON PATHOGENICITY OF MYCOSPHAERELLA-GRAMINICOLA (ANAMORPH SEPTORIA-TRITICI)

Populations of Mycosphaerella graminicola isolated from winter wheat c ultivars near crop maturity were subsequently evaluated on seedlings o f the same wheat cultivars in the greenhouse. Significant pathogen pop ulation effects, cultivar effects, and pathogen population x cultivar interactions were demonstrated. Pathogen populations isolated from sus ceptible cultivars produced higher levels of disease, averaged over cu ltivars, than did populations isolated from moderately resistant or re sistant cultivars, indicating that susceptible cultivars selected for higher levels of pathogen aggressiveness in the field. In addition, pa thogen populations were more virulent on the cultivars they were isola ted from in the field than on other cultivars, indicating selection fo r cultivar-specific virulence.