Cytological Study of 2n Pollen Formation in Musa

Current Musa breeding strategies are complex and time consuming involving the selection of tetraploids from 3x - 2x crosses. Secondary triploids are then obtained by crossing these tetraploids with diploids. Considering the very low hybrid seed set, routine embryo rescue procedures of hybrid seeds and the long growth cycle of banana, it takes approximately 10 - 12 years to produce an acceptable banana hybrid. The banana breeding process could benefit tremendously if triploid bananas could be obtained directly from 2x - 2x crosses through the process of unilateral sexual polyploidization. There are few reports on the mechanisms through which Musa species produce 2n pollen. This study investigated the type of meiotic irregularities that lead to 2n pollen formation in diploid, triploid and tetraploid Musa accessions using cytological analyses. The results showed that aberrations in cytokinesis and karyokinesis during microsporogenesis are possible mechanisms for 2n pollen formation in Musa. The meiotic aberrations described in this study have implications for Musa breeding. It appears that 2n pollen formation in Musa occurs via both first division restitution (FDR) and second division restitution (SDR). FDR is said to be more promising in transferring more heterozygosity from parents to offspring.