Inheritance of Apospory in Buffelgrass

Previous studies on inheritance of monopolar ( Panicum type) apospory in the Panicoideae resulted in three widely different genetic models and mutually incompatible data sets. We report additional data for tetraploid buffelgrass [ Pennisetum ciliate (L.) Link = Cenchrus ciliaris L.] and attempt to reconcile earlier studies. Sexual buffelgrass plant B‐2s and five sexual progeny from open pollination of B‐2s were self pollinated and intercrossed. Three obligately aposporous half‐siblings from open pollination of B‐2s and two other aposporous plants were used as male parents in hybridizations with the sexual plants. Selling and crossing among sexual plants gave only sexual progeny. Crosses of sexual × aposporous plants gave progeny segregating for sexual (Polygonum type) and aposporous ( Panicum type) embryo sacs at ratios near 15:13 or 3:8 depending upon the aposporous parent. Two earlier models postulating that Panicum type apaspary was regulated by two disomic genes could not account for all types of segregation observed. Assuming random assortment of chromatids, the data fit a model earlier proposed for Panicum maximum Jacq. that postulates expression of apospory requires the dominant allele ( A ) of a single tetrasomieally inherited locus. Published and present data could be accommodated by a two‐locus model for tetrasomic transmission in which the dominant allele ( A ) of one locus is required for apaspory but is hypastatic to the dominant allele ( B ) of the second locus which confers sexuality. Alternatively, it is suggested that tetraploid parents thought to be purely sexual in earlier studies actually were highly sexual, facultative apamicts that yielded segregating progenies after self pollination.