INHERITANCE OF APOSPORY IN BUFFELGRASS

Previous studies on inheritance of monopolar (Panicum type) apospory i n the Panicoideae resulted in three widely different genetic models an d mutually incompatible data sets. We report additional data for tetra ploid buffelgrass [Pennisetum ciliare (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 po llinated and intercrossed. Three obligately aposporous half-siblings f rom open pollination of B-2s and two other aposporous plants were used as male parents in hybridizations with the sexual plants. Selfing and crossing among sexual plants gave only sexual progeny. Crosses of sex ual x 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 postul ating that Panicum type apospory was regulated by two disomic genes co uld not account for all types of segregation observed. Assuming random assortment of chromatids, the data fit a model earlier proposed for P anicum maximum Jacq. that postulates expression of apospory requires t he dominant allele (A) of a single tetrasomically inherited locus. Pub lished 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 apospory but is hypostatic to the dominant allele (B) of the second locus which confers sexuality. Alternatively, it is sug gested that tetraploid parents thought to be purely sexual in earlier studies actually were highly sexual, facultative apomicts that yielded segregating progenies after self pollination.