COMPONENTS OF RESISTANCE IN BARLEY TO STEM RUST - RECEPTIVITY, UREDINIOSPORE PRODUCTION, LATENT PERIOD, AND INFECTION RESPONSE IN ADULT PLANTS

Resistance in barley (Hordeum vulgare) to stem rust, caused by Puccini a graminis f.sp. tritici, is often variably expressed. This study was undertaken to evaluate several components of stem rust resistance in t he barley cultivars or lines Tupper, Robust, Q21861, SB90585, SB91702, and Harrington and to compare them with the susceptible wheat cultiva r Little Club (Triticum aestivum). Stems of adult plants were quantita tively inoculated with urediniospores of races QCC, QFC, and TPM of P. graminis tritici. Significant differences in receptivity, urediniospo re production, and latent period were observed among the barley lines and between all barley lines and Little Club wheat. The degrees of rec eptivity and the levels of urediniospore production on the barley line s were related to the presence or absence of the specific resistance g enes Rpg1, rpg4, and possibly additional noncharacterized gene(s). Rec eptivity was the most strongly expressed of all of the components meas ured. Receptivity, spore production, and infection response were highl y correlated to each other, but only infection response was significan tly correlated to latent period. The usefulness of measuring these com ponents to evaluate resistance in barley breeding is discussed.