Inheritance of male sterility in Trifolium hirtum All

The inheritance of male sterility was studied using a set of intra and interpopulation crosses from Californian populations of rose clover (Trifolium hirtum All.). The F2 gave higher frequencies of male steriles in interpopulation crosses than in intrapopulation crosses. Several F2 families gave ratios that were compatible with models of two and three complementary genes. However, the frequency distribution of male sterility among F3 families rejected such models. Given that single and two gene models were rejected, we interpret the results using a cytoplasmic-nuclear model with more than two restorer loci which is at least consistent with the observed results.