GENETIC ANALYSES OF MALE-FERTILITY RESTORATION IN WHEAT .7. A FERTILITY-INHIBITING GENE

The cytoplasm of Triticum timopheevii Zhuk. has no apparent adverse effect on the cytoplasmic male-sterile (CMS) plants of T. aestivum L. However, compared to the seed from A-line/R-line crosses, seed from A-line/B-line crosses have rough epidermis and reduced viability. Our objective was to compare the seed viability and fertility in plants with RfRf, Rfrf, or hemizygous Rf genes. We used CMS 'Chris' monosomics 1A and 6B, and four R-lines. Lines L19 and L22 have Rf1 on chromosome 1A, and L11 and L13 have Rf4 on chromosome 6B. Sixteen BC1F1 families were obtained by crossing CMS Chris monosomics 1A and 6B to the four R-lines and backcrossing 1A and 6B monosomic F1's to the corresponding R-lines and euplasmic Chris. Eight controls were obtained by crossing four euploid F1's to the corresponding R-lines and euploid Chris. The results showed that (i) Chris has a fertility inhibiting (Fi) gene and all four R-lines have an fi and a defective-seed (dfs) gene, (ii) fertility and seed viability were reduced to a greater extent in 6B monosomics than in 1A monosomics, (iii) aneuploidy affected the expression of Rf (and/or positive modifiers) and increased the expression of dfs more in crosses of L13 and L22 with a higher male-fertility restoration potential than in crosses of L11 and L19 with a lower fertility restoration potential, and (iv) RfRf and FiFi were epistatic to dfsdfs, FiFi reduced the expression of Rfrf, but Djs improved the viability of seed with rfrf fifi Dfsdfs embryos. It is proposed that the breeding of CMS A-lines with fi, and R-lines with positive modifiers of Rf genes, may facilitate male fertility restoration in Rfrf fifi wheat hybrids.