Abstract
This study aims to understand the genetic diversity of traditional Oceanian starchy bananas in order to propose an efficient conservation strategy for these endangered varieties. SSR and DArT molecular markers are used to characterize a large sample of Pacific accessions, from New Guinea to Tahiti and Hawaii. All Pacific starchy bananas are shown of New Guinea origin, by interspecific hybridization between Musa acuminata (AA genome), more precisely its local subspecies M. acuminata ssp. banksii, and M. balbisiana (BB genome) generating triploid AAB Pacific starchy bananas. These AAB genotypes do not form a subgroup sensu stricto and genetic markers differentiate two subgroups across the three morphotypes usually identified: Iholena versus Popoulu and Maoli. The Popoulu/Maoli accessions, even if morphologically diverse throughout the Pacific, cluster in the same genetic subgroup. However, the subgroup is not strictly monophyletic and several close, but different genotypes are linked to the dominant genotype. One of the related genotypes is specific to New Caledonia (NC), with morphotypes close to Maoli, but with some primitive characters. It is concluded that the diffusion of Pacific starchy AAB bananas results from a series of introductions of triploids originating in New Guinea area from several sexual recombination events implying different genotypes of M. acuminata ssp. banksii. This scheme of multiple waves from the New Guinea zone is consistent with the archaeological data for peopling of the Pacific. The present geographic distribution suggests that a greater diversity must have existed in the past. Its erosion finds parallels with the erosion of cultural traditions, inexorably declining in most of the Polynesian or Melanesian Islands. Symmetrically, diversity hot spots appear linked to the local persistence of traditions: Maoli in New Caledonian Kanak traditions or Iholena in a few Polynesian islands. These results will contribute to optimizing the conservation strategy for the ex-situ Pacific Banana Collection supported collectively by the Pacific countries.
Highlights
Bananas are widely distributed and cultivated throughout all the Pacific Islands
The surveys conducted in Vanuatu showed that mostly all the common banana types are grown there today, which is a result that may be extended without any great risk to all the islands of the Pacific
This often involves sweet types, which must have appeared as attractive innovations in this traditional starchy banana zone: the usual dessert AAA of the Cavendish type or similar, the sweet AAB introduced from India, and the AA of the ‘Sucrier’ type that are found in all production regions
Summary
Bananas are widely distributed and cultivated throughout all the Pacific Islands. All currently cultivated varieties fall into two distinct introduction waves. The most recent wave followed the exploratory travels of Captain Cook at the end of the 18th century, with numerous introductions from almost all the other banana areas in the world [1]. It occurred well after a first ‘Oceanian’ wave, which brought traditional starchy bananas to all the Pacific Islands. Like most other cultivated species, these traditional varieties were introduced to the Pacific Islands and their dissemination is directly related to the original eastward peopling of the Pacific from South East (SE) Asia, as described by geneticists, ethnologists, ethnobotanists, linguists and archaeologists [2,3,4,5,6,7,8]
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