Evaluation of pollen fertility of diploid and doubled-diploid clones of Mlali and their potential use for banana breeding

Past phylogenetic studies pointed out some Mlali clones (AA) as the 2N gamete donor parent of Cavendish (AAA) and Gros Michel (AAA) varieties, revealing their potential for Musa breeding. Nevertheless, cultivated bananas are usually known to be highly sterile at diploid and trip bid levels, making banana crosses difficult. Therefore, it is necessary to investigate the floral biology of these Mlali clones to determine their capacity to generate progenies by crosses. Pollen fertility of both diploid and doubled-diploid Mlalis (as donor of diploid gametes) was evaluated by different approaches. At anthesis, Alexander staining technique has shown that up to 70% of haploid and diploid pollen was viable. Pollen viability was confirmed in test crosses with Musa wild accessions presenting no fertility problems. These results were then correlated with post-meiotic observations at the tetrad stage: 70% were regular tetrads in the diploid and doubled-diploid clones whereas the remaining cells were aggregated under forms of pentads and hexads, and more rare heptads leading probably to aborted microspores. Fine observations of the irregular tetrads suggested that meiotic errors occurred during both first and second mitosis of the meiosis. These preliminary results suggest that doubled-diploid Mlali clones (AAAA) might be useful male parents with high breeding potential for the synthesis of new disease-resistant AAA export bananas. (Résumé d'auteur