DIFFERENTIAL SUPPRESSION OF STRIPE RUST RESISTANCE IN SYNTHETIC WHEATHEXAPLOIDS DERIVED FROM TRITICUM-TURGIDUM SUBSP DICOCCOIDES AND AEGILOPS-SQUARROSA

The expression of resistance to stripe rust of wheat, conditioned by f our Aegilops squarrosa (DD, 2n = 14) and 11 Triticum turgidum subsp. d icoccoides (AABB, 2n = 28) accessions, was studied by testing 22 synth etic hexaploids (AABBDD, 2n = 42) with five stripe rust races in the s eedling stage and two races in the adult plant stage. Resistance in on e or both parents was frequently suppressed in the synthetic hexaploid s, indicating the presence of suppressor genes on the AB and D genomes . Specificity was apparent because the putative suppressor genes affec ted the expression of specific resistance genes, although not with all races nor in all growth stages. The results and data from F-1, and F- 2 populations derived from crosses between two synthetic hexaploids wi th the same T. t. dicoccoides parent but with different A. squarrosa p arents revealed that several recessively inherited suppressor genes on the D genome seemed to be involved. A possible mechanism explaining t hese results and the variable mode of action of suppressors are discus sed.