Diversity and phylogenetic relationships among wild and cultivated bananas (Silk-AAB) revealed by SSR markers

Genetic diversity and phylogenetic studies were undertaken to identify possible progenitors of Silk banana varieties for use in conventional breeding. Genetic diversity and phylogeographical relationships among 33 accessions of banana belonging to the Silk (AAB) sub-group were studied and compared with their wild progenitors. Seventy-eight alleles were identified among the test accessions, with a mean frequency of 6.5 alleles per locus, and the polymorphism information content (PIC) values varied from 0.28 - 0.55, with an average of 0.41. The co-phenetic correlation coefficient (r) was 0.9, suggesting a good fit between the dendrogram and the similarity matrix. UPGMA cluster analysis based on Sequential Agglomerative Hierarchical and Nested (SAHN) clustering methods exhibited an eccentric lineage of Khungsong wild' (Musa balbisiana-BB) with Silk accessions, implying its putative ancestry. The microsatellite markers selected for this study clearly distinguished wild M. acuminata, wild M. balbisiana, and bispecific cultivated Silk accessions. The results suggest that, irrespective of geographical origin, the Silk group of bananas have a narrow genetic base, with > 80% similarity, and could be derived from a single genotype. This situation offers limited opportunities to improve resistance against Fusarium wilt and Sigatoka leaf spot complex through classical breeding, and will necessitate the use of other biotechnological approaches. This study also revealed a grouping of Khungsong wild' (BB) with Silk group accessions instead of wild M. balbisiana and wild M. acuminata, suggesting its possible involvement in the evolution of the Silk group.