POSTSEEDLING RESPONSE OF WHEAT TO STEM RUST

Abstract

The seedling and postseedling reactions of five cultivars of Triticum aestivum L. to eight races of Puccinia graminis f. sp. tritici Eriks. and E. Henn. were compared under Kenya growing conditions. The seedling and postseedling reactions of Florence Aurore to eight races of stem rust were similar. The cultivars Hope, Africa Mayo, Kenya Page, and Conley differed from Florence Aurore in that seedlings of these cultivars were susceptible to several races, whereas postseedlings expressed a degree of resistance to these same races. Postseedling resistance may be identical with horizontal resistance. The stage of growth during which resistance became effective was determined by inoculating each cultivar at various stages of growth. The reaction class of Hope and Africa Mayo changed from susceptible to moderately susceptible between the fourth- and the fifth-leaf stage to races EA4(295) and EA8(40); the reaction class of Kenya Page and Conley changed from susceptible to moderately resistant to both races at about the third-leaf stage. The stage of growth during which resistance became expressed was independent of the test race.