NUCLEAR-CYTOPLASMIC INTERACTIONS IN RESTORATION OF MALE-FERTILITY IN THE 9E AND A4 CMS-INDUCING CYTOPLASMS OF SORGHUM

The genetics of male-fertility restoration in sorghum in the ''9E'' an d A4 CMS-inducing cytoplasms, was studied by crossing a number of fert ility restorer lines of Al cytoplasm to CMS lines [9E]T x 398 and [A4] T x 398 and the line [9E]Milo-10, which was obtained by backcrossing M ilo-10 to [9E]T x 398. It was revealed that both A4 and ''9E'' cytopla sms are characterized by a sporophytic mode of restoration of male fer tility. Depending on the nuclear background of the male parents, ferti lity restoration was controlled by one or two dominant genes. Fertilit y-restorer genes of one of the tester lines, KVV-114, were effective i n [9E]T x 398 but could not restore [9E]Milo-10. A fertile line obtain ed from the fertile hybrid [9E]T x 398/KVV-112, with ''9E'' cytoplasm: also failed to restore [9E]Milo-10. In a number of hybrid combination s with both A4 and ''9E'' cytoplasms a novel and unusual phenomenon of gradual restoration of male fertility in subsequent backcross generat ions was observed. Pollen from the fertile revertents did not transmit fertility restoration in progeny from crosses with the original CMS l ine and was poorly transmitted in sib-crosses. The appearance of ferti le revertants and the different reactions of different CMS lines with the same cytoplasm in test-crosses may be caused by the action of rece ssive nuclear gents of the recurrent male parents that were accumulate d during backcrossing; these may induce changes in cytoplasmic genes c ontrolling CMS.