Abstract
BackgroundCultivated bananas are large, vegetatively-propagated members of the genus Musa. More than 1,000 cultivars are grown worldwide and they are major economic and food resources in numerous developing countries. It has been suggested that cultivated bananas originated from the islands of Southeast Asia (ISEA) and have been developed through complex geodomestication pathways. However, the maternal and parental donors of most cultivars are unknown, and the pattern of nucleotide diversity in domesticated banana has not been fully resolved.Methodology/Principal FindingsWe studied the genetics of 16 cultivated and 18 wild Musa accessions using two single-copy nuclear (granule-bound starch synthase I, GBSS I, also known as Waxy, and alcohol dehydrogenase 1, Adh1) and two chloroplast (maturase K, matK, and the trnL-F gene cluster) genes. The results of phylogenetic analyses showed that all A-genome haplotypes of cultivated bananas were grouped together with those of ISEA subspecies of M. acuminata (A-genome). Similarly, the B- and S-genome haplotypes of cultivated bananas clustered with the wild species M. balbisiana (B-genome) and M. schizocarpa (S-genome), respectively. Notably, it has been shown that distinct haplotypes of each cultivar (A-genome group) were nested together to different ISEA subspecies M. acuminata. Analyses of nucleotide polymorphism in the Waxy and Adh1 genes revealed that, in comparison to the wild relatives, cultivated banana exhibited slightly lower nucleotide diversity both across all sites and specifically at silent sites. However, dramatically reduced nucleotide diversity was found at nonsynonymous sites for cultivated bananas.Conclusions/SignificanceOur study not only confirmed the origin of cultivated banana as arising from multiple intra- and inter-specific hybridization events, but also showed that cultivated banana may have not suffered a severe genetic bottleneck during the domestication process. Importantly, our findings suggested that multiple maternal origins and a reduction in nucleotide diversity at nonsynonymous sites are general attributes of cultivated bananas.
Highlights
Cultivated bananas are the fourth most important crop in developing countries, and it has been proposed that they derive from the domestication of genus Musa [1,2]
This hypothesis was subsequently confirmed by genetic studies of the genus Musa which indicated that at least four wild species, M. acuminata, M. balbisiana, M. schizocarpa and M. textilis, have contributed to the gene pools of domesticated bananas [1,8,9]
Details of the Waxy and alcohol dehydrogenase 1 (Adh1) gene structures and the primer sequences used are given in Table S1 and Figure S1
Summary
Cultivated bananas are the fourth most important crop in developing countries, and it has been proposed that they derive from the domestication of genus Musa [1,2]. There have been extensive discussions about the identities of the progenitors of domesticated banana; M. acuminata and M. balbisiana have been proposed as the wild parents of modern bananas [6] This hypothesis was subsequently confirmed by genetic studies of the genus Musa which indicated that at least four wild species, M. acuminata (donor of the A genome), M. balbisiana (donor of the B genome), M. schizocarpa (donor of the S genome) and M. textilis (donor of the T genome), have contributed to the gene pools of domesticated bananas [1,8,9]. At present, these four wild relatives are still widespread in the tropical and subtropical regions of Asia. The maternal and parental donors of most cultivars are unknown, and the pattern of nucleotide diversity in domesticated banana has not been fully resolved
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