Cytoplasmic‐Genic Male‐Sterility Systems in Sorghum1

Essentially all sorghum, Sorghum bicolor (L.) Moench, hybrids are made with a single cytoplasmic‐genic sterility system. In an attempt to derive new cytoplasmic‐genic male‐sterility systems in sorghum, recently introduced lines of diverse types from widespread geographic locations were intercrossed and backcrossed. Three male sterile from this program were tested to determine their cytoplasmic diversity for induction of male sterility. Fertility of the F1 hybrids from crosses of each sterile line with a series of tester lines was compared with fertility of hybrids from crosses of a currently used sterile (‘A Tx3197’) with the same testers. Differential sterility responses indicated that each of these cytoplasms probably differ from milo cytoplasm of A Tx3197. Of these, the line with IS 12662C cytoplasm is the most desirable sterile and has been released as ‘A2 Tx2753’. Differential sterility responses among the three steriles also indicated possible cytoplasmic differences among them. Because each of these steriles was in an early generation and differed in nuclear genes, definitive conclusions must await the testing of more nearly isocytoplasmic lines developed by incorporating a common nuclear genotype into each cytoplasmic source.