CHROMOSOMAL LOCATION OF GENES FOR STEM RUST RESISTANCE DERIVED FROM WALDRON WHEAT

The chromosomal locations of genes for resistance to stem rust (Puccin ia graminis Pers.: Pers. f. sp. tritici Eriks. and E. Henn.) in the wh eat (Triticum aestivum L.) cultivar 'Waldron' (WDR) were determined by monosomic analyses. Wheat lines WDR-B1, -C2, -E4, and -F1, which have single genes for resistance to stem rust derived previously from WDR sel. 'Little Club', were crossed onto a complete set of 21 'Chinese Sp ring' monosomics. The F-2 and backcross-F-1 (BC1F1) seedlings from eac h of the 84 crosses were tested for reaction to culture 111-SS2 (CRL-L CBB) of stem rust, and a few selected segregants were analyzed cytolog ically for chromosome number. The F-2 from 2 crosses of WDR-C2, -E4 an d -F1 and the BC1F1 from 2 crosses of WDR-F1 were tested also with cul ture Or11c (CRL-QBCN). Significant deviations from disomic ratios towa rds monosomic ratios in the F-2 and BC1F1 were used to determine which chromosomes carried the genes for resistance. Cytological analyses of certain BC1F1 and susceptible F-2 plants were used to help identify t he location of the genes for rust resistance. WDR-B1 has a gene, herei n designated Sr41, for resistance on chromosome 4D. WDR-C2 has a gene on chromosome 7A that may be the same as one previously designated SrW ld2. WDR-E4 has a gene on chromosome 2A, possibly SrWld1, which is eff ective against most or all North American stem rust cultures. WDR-F1 h as a gene on chromosome 6B that is the same as or similar to Sr11.