Relationships Among Male‐Sterility Inducing Cytoplasms of Sorghum1

Cytoplasmic‐nuclear male steriles are used as female parents in the production of hybrid seed of sorghum, Sorghum bicolor (L.) Moench. A single male‐sterility inducing cytoplasm is most often used in the female parents, resulting in uniformity of cytoplasm in hybrids and also a restriction on nuclear diversity. The purpose of the present study was to identify diverse malesterility inducing cytoplasms. Seed set and other characteristics of hybrids of sorghum were studied to determine differences in fertility response and related characteristics among the cytoplasms of male‐sterile female parents. Thirteen near‐isonuclear female parents with cytoplasms from diverse introduced sources were crossed by eight male parents, and the progeny were grown at eight locations. From seed‐set, anther, and pollen characteristics five groups were identified. Cytoplasms from IS6271C, IS2266C, IS3579C, IS7502C, and IS6705C were not distinguished from milo cytoplasm. Cytoplasm from IS12662C differed from milo in degree of fertility restoration in hybrids and was somewhat similar to IS3063C, IS1056C, and IS2801C. Another group, composed of IS1112C and IS12565C, was distinct in that most male parents produced highly sterile hybrids when crossed with these male steriles. Another cytoplasm, from IS7920C, differed from all the other cytoplasmstudied in its effects on seed‐set, anther, and pollen characteristics. It is concluded that among these cytoplasms there are at least four distinct groups in their effects on fertility characteristics. They have potential for providing diversity among parents and hybrids in sorghum, but their utility for such purposes remains to be tested.