GENES FOR RESISTANCE TO STRIPE RUST IN 4 SPRING WHEAT-VARIETIES .2. ADULT-PLANT RESPONSES

The stripe rust resistant spring wheat (Triticum aestivum L.) varietie s 'Anza', 'Glennson 81', 'Ollanta', and 'Yecora Rojo' gave 1,2,2, and 2-gene segregations, respectively, in hybrids with susceptible 'Jupate co 73' when inoculated in field conditions at Davis, California USA wi th Puccinia striiformis West. pathotype CDL-6 and rated at past-headin g stage. Intercrosses of these varieties, 'Anza'/'Yecora Rojo' was not studied, permitted the following conclusions about the genes expresse d in adult plants: 'Anza', one recessive gene; 'Glennson 81', two domi nant genes; 'Ollanta', two genes, at least one is dominant; and 'Yecor a Rojo'; one dominant and one recessive gene, one of which is common w ith 'Ollanta'. The resistance genes in these varieties, which expresse d resistance in the seedling stage, were believed to be effective at t he adult stage. Thus, seven resistance genes were identified in the fo ur varieties. The genotypes were designated for the purposes of this s tudy as follows: 'Anza', YrA YrH; 'Glennson 81', Yr9, YrJ, 'Ollanta' Y I L YrD; and 'Yecora Rojo, YrC YrD. It was recommended that these and other Yr genes be used as multiple gene complexes to increase durabili ty of resistance to P. striiformis, an organism known to evolve virule nce rapidly in field conditions. The demonstrated durability of 'Anza' in California may be a result of its combination of resistance allele s at two loci.