GENETIC ANALYSES OF MALE-FERTILITY RESTORATION IN WHEAT .5. ANOMALOUS RESULTS OF A MONOSOMIC ANALYSIS

A fertile line (L222) of common wheat (Triticum aestivum L.), with cytoplasm of T. timopheevii Zhu., and rf1 and rf4 alleles of the major Rf genes on chromosomes 1A and 6B, respectively, was developed and analyzed for male fertility-restoring genes. L222 descended from 1 of the 11 partially fertile monosomics in the backcross progeny of cytoplasmic male-sterile (cms) Chris monosomic 1A/L22 (Rf1Rf1rf4rf4), F1 monosomic 1A//euploid Chris. Additional fertile monosomics were obtained from a second backcross of partially fertile monosomics in F2 and F3 of the same cross. In their selfed progenies, monosomics and disomics were increasingly fertile, even though they were expected to have neither of the major Rf genes. L222 was analyzed for chromosomal location of Rf gene(s). A monosomic set of euplasmic 'Chris' and two tester stocks, cms 'Era' and cms Chris, were used for monosomic analysis. Plants were grown in a greenhouse at Fargo, ND. Results indicate that a major Rf gene was retained on chromosome 1A. An abnormally high incidence of univalent shift or contamination may explain the presence of Rf1 on chromosome 1A of L222, but this was unlikely to occur in such a high frequency as to produce several fertile monosomics in three different backcross progenies. Two of the fertile monosomics were correctly identified as mono-1A by testcrossing them to Chris ditelosomic 1AS. Therefore, a hypothesis was proposed that a mutagenic (mtg) gene mutated rf1 to Rf1 in some of the plants that were monosomic for chromosome 1A. The original Rf1 and the mutant Rf1 are both located on the short arm of chromosome 1A, but allelism was not tested. The proposed genotypes of L222, Chris, and Era are Rf1Rf1 fifi, rf1rf1 FiFi; and Rf1Rf1 fifi, respectively.