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Gene Sr21 for resistance to Puccinia graminis tritici in five hexaploid derivatives of the diploid Triticum monococcum was located in chromosome 2A. Since only one chromosome was involved in resistance, abnormal ratios found in some diploid wheat crosses and in one hexaploid derivative were attributed to differential transmission of gametes rather than to gene duplication in the diploid wheat sources. By using 2AS and an unknown telocentric presumed to be 2AL in telocentric mapping, Sr21 was placed 2�4�0�9 recombination units from the centromere in 2AL.

The gene Sr22 conditioning low reaction to Puecinia graminis tritid was located by telocentric mapping on chromosome 7 AL at 27 � 4 crossover units from the centromere. Sr22 was approximately 2 crossover units from en-AI (ehlorina) and 41 units from PmI for low reaction to Erysiphe graminis trifid; however, the order of Sr22 and en-AI relative to PmI was not resolved. Maximum recombination between PmI, Lr20 and SrI5, for low reactions to E. graminis tritici, P. reeondita and P. graminis tritid respectively, was estimated to be O' 3 crossover units at the 95 % probability level.

Two techniques used for genetic transfer of stem rust resistance from einkorn (T. monococcum) to hexaploid wheat are described. Success of direct interspecific hybridization between wheat and einkorn was confined to the wild form, and is attributed to differences in survival and development of F 1 hybrids rather than crossability between the two species or germination of hybrid grains. Meiotic pairing between A genome chromosomes in interspecific hybrids was shown to be significantly lower in AABD than in AAB hybrids. These two interspecific hybrids also showed a different distribution pattern of functional female gametes.

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