Dominant male sterility in sorghum: effect of nuclear background on inheritance of tissue-culture-induced mutation

Occurrence of genetic instability and formation of stable mutations are basic genetic processes. This study demonstrates that nuclear background may influence the formation of stable dominant nuclear gene of male sterility (MS) on the basis of unstable mutation, which was induced in tissue culture of the sorghum haploid (cv. Milo-145). The mutants with complete or partial MS segregated in variable ratios in the progenies of diploid regenerants were obtained from different experiments on cultivation of haploid tissues. In the Milo-145 genetic background the mutation demonstrated somatic instability and was gradually eliminated by self-pollination of partially sterile plants. Hybridization of the MS-plants with the sorghum line SK-723, a fertility-restorer of the cytoplasmic MS A1 (milo) type, maintained the induced mutation. By repeated backcrossing of MS-plants with SK-723, the male-sterile versions of this line (SK-723- Ms _tc ) have been created. In BC-generations, fertile, partially and completely sterile plants were observed. The MS-plants from BC-generations are proposed to contain a dominant gene Ms _tc while fertile plants were ms _tc / ms _tc homozygotes. Crossing the original MS-plants with SK-723 was a key factor in stabilization of the Ms _tc gene. Dominant expression of the Ms _tc was observed in male-sterile versions of other sorghum lines created by backcrossing to SK-723- Ms _tc . The lines fertility-restorers for this mutation have been revealed. In the crosses of restored F₁ hybrids with emasculated plants of the non-restoring line, the Ms _tc has been transferred through the pollen and manifested in the F₁ generation. The possibility of the Ms _tc originating as a result of interaction of an unstable allele of the Milo-145 with the SK-723 genome is discussed.