Inheritance of apospory in babliagrass, Paspalum notatum

Previous studies on the inheritance of aposporous apomixis in bahiagrass showed a wide range of segregation ratios in crosses involving sexual and aposporous apomietic plants. The F-1 progenies were classified through a visual progeny test carried Out on few F-2 plants. The number of sexual F(1)s highly exceeded the apomictics leading to the conclusion that apomixis was controlled by a few recessive genes, The present study examines the inheritance of apospory in bahiagrass. A sexual plant was self-pollinated and crossed with an aposporous apomictic plant as pollen donor. Backcross and F-1 progenies were obtained in several combinations. All self-pollinated sexual plants or sexual x sexual crosses produced progenies free of apospory. All crosses involving a sexual and an apomictic plant produced approximately three times more apospory-free plants than plants with apospory. Bahiagrass is of autotetraploid origin and hence is expected to display tetrasomic inheritance. The most widely accepted genetic model for inheritance of apospory in tropical grasses is a single dominant gene with tetrasomic inheritance. In the present experiments none of the apospory-free F(1)s segregated for the apospory trait indicating that it is most likely a dominant character. However, the observed results fit better a modified model: tetrasomic inheritance of a single dominant gene with pleiotropic effect and incomplete penetrance, The excess of apospory-free plants in the F-1 progeny could be ascribed to some distortion in the segregation pattern due to a pleiotropic lethal effect of the dominant A allele with incomplete penetrance, Alternatively, partial lethality of factors linked to aposporous gene may account for segregation distortion against apospory.