Barley cultivars Kitchin (C.I. 1296) and Jet (C.I. 967), resistant to scald (incited by Rhynchosporium secalis (Oud.) Davis), and cultivars Tifang (C.I. 14373), C.I. 9819, and C.I. 7584, resistant to net blotch (incited by Pyrenophora teres Drechs.), were crossed to the primary trisomics in the cultivar Betzes. F2 segregation ratios were studied to determine chromosomal location of the resistance genes. Kitchin was found to contain a single scald-resistance gene, Rrs9, on chromosome 4. Jet contained scald-resistance genes rrs1 and rrs6 on chromosomes 3 and 4, respectively. Tifang contained a single gene, Rpt1a, for net-blotch-resistance on chromosome 3. C.I. 7584 contained a single net-blotch-resistance gene, Rpt3d, on chromosome 2. C.I. 9819 contained net-blotch-resistance genes Rpt1b and Rpt2c on chromosome 3 and 5. Some uses of this information are discussed.

The wheat varieties, 'P.I. 178383' and 'Chinese 166' (Triticum aestivum), were each found to carry an incompletely dominant major gene for resistance to a single pathogenic type of Puccinia striiformis. In addition, an undetermined number of minor genes segregated in such a way that in certain combinations they conferred moderate resistance and modified the action of the major genes. The rust readings were made on seedling plants grown in strictly controlled-environment chambers that simulated natural conditions. The action of the major genes was not affected by different temperature profiles, but the minor genes gave better resistance at a higher temperature profile than at a lower temperature profile.

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