Fertility restoration effects of R113 chromosomes of wheat

Production of fully fertile F{dollar}sb1{dollar} hybrids using the Triticum timopheevii (Zhuk.) Zhuk. cytoplasmic male-sterility system in common wheat (T. aestivum L.) is difficult to achieve. Examination of individual fertility restoring (Rf) genes in T. timopheevii cytoplasm may provide the information needed to breed more suitable R-lines and A-lines. Individual chromosomes of R113 were studied by developing chromosome substitution lines for each of the 21 chromosomes of R113 from crosses to Chris monosomics. R113 chromosome substitution lines (R-sub lines) were developed by selfing monosomic F{dollar}sb1{dollar} plants. The 381 F{dollar}sb7{dollar} R-sub lines were crossed to two A-lines, mst-Chris and mst-Era. A total of 335 and 327 F{dollar}sb1{dollar} progenies were evaluated for mst-Chris and mst-Era crosses, respectively. The F{dollar}sb1{dollar} progenies having chromosomes 1A, 2A, and 6B of R113 produced a high level of fertility (seed/spikelet) in bagged spikes and few or no male sterile plants. Two Rf genes, probably Rf{dollar}sb6{dollar} located on 3A and Rf{dollar}sb1{dollar} on 1A of R113, had weaker restoring effects than Rf{dollar}sb4{dollar} on 6B. R-sub lines of chromosomes 2A and 6A produced more male sterile F{dollar}sb1{dollar} plants and appeared to have dominant fertility restoration inhibitor genes. R-sub lines of chromosome 5D produced no male sterile F{dollar}sb1{dollar} plants in mst-Era crosses suggesting that mst-Era has a fertility restoring factor on 5D which is not present in mst-Chris. Male sterile F{dollar}sb1{dollar} plants were backcrossed to their respective R-sub lines to develop a new set of A-lines. Eight R-sub lines produced TCF{dollar}sb1{dollar}, {dollar}rm BCsb1Fsb1{dollar}, and {dollar}rm BCsb2Fsb1{dollar} progenies that were male sterile in T. timopheevii cytoplasm. Eighteen male sterile (timopheevii) R-sub lines were crossed to four single gene R-lines, L11, L13, L19, and L22, to evaluate fertility restoration. Crosses of single Rf gene R-lines to mst-Era produced more fertile progeny than mst-Chris crosses. R-line L11 and L22 produced lowest and highest F{dollar}sb1{dollar} fertility, respectively. R-sub lines 6A-07 and 7D-12 produced nearly male sterile plants in T. timopheevii cytoplasm and high fertility in crosses to single gene R-lines. Thus, partial or complete elimination of the dominant inhibitors may be necessary to produce A-lines that can be easily restored.