Abstract
BackgroundBorassus flabellifer or Asian Palmyra palm is an important crop for local economies in the South and Southeast Asia for its fruit and palm sugar production. Archeological and historical evidence indicated the presence of this species in Southeast Asia dating back at least 1500 years. B. flabellifer is believed to be originated in Africa, spread to South Asia and introduced into Southeast Asia through commercial routes and dissemination of cultures, however, the nature of its invasion and settlement in Thailand is unclear.ResultsHere, we analyzed genetic data of 230 B. flabellifer accessions across Thailand using 17 EST-SSR and 12 gSSR polymorphic markers. Clustering analysis revealed that the population consisted of two genetic clusters (STRUCTURE K = 2). Cluster I is found mainly in southern Thailand, while Cluster II is found mainly in the northeastern. Those found in the central are of an extensive mix between the two. These two clusters are in moderate differentiation (FST = 0.066 and NM = 3.532) and have low genetic diversity (HO = 0.371 and 0.416; AR = 2.99 and 3.19, for the cluster I and II respectively). The minimum numbers of founders for each genetic group varies from 3 to 4 individuals, based on simulation using different allele frequency assumptions. These numbers coincide with that B. flabellifer is dioecious, and a number of seeds had to be simultaneously introduced for obtaining both male and female founders.ConclusionsFrom these data and geographical and historical evidence, we hypothesize that there were at least two different invasive events of B. flabellifer in Thailand. B. flabellifer was likely brought through the Straits of Malacca to be propagated in the southern Thailand as one of the invasive events before spreading to the central Thailand. The second event likely occurred in Khmer Empire, currently Cambodia, before spreading to the northeastern Thailand.
Highlights
Borassus flabellifer or Asian Palmyra palm is an important crop for local economies in the South and Southeast Asia for its fruit and palm sugar production
Previous genetic studies using various types of DNA markers showed that B. flabellifer populations have very low genetic diversity [14,15,16,17], and this was concerned as a potential threat to a sustainable use as the species is in decline through extensions of farmland, urbanization and its extremely long juvenile stage
There are ancient scripts describing the presence of B. flabellifer in Laos in the past 1500 years [38, 39], we envisage that B. flabellifer in the northeastern Thailand was likely introduced from the areas, where it is Cambodia, rather than Laos or Vietnam. This is because our result showed that the cluster II is concentrated at the lower part of the northeastern Thailand next to the Cambodia border, which has no major natural barriers
Summary
Borassus flabellifer or Asian Palmyra palm is an important crop for local economies in the South and Southeast Asia for its fruit and palm sugar production. B. flabellifer is believed to be originated in Africa, spread to South Asia and introduced into Southeast Asia through commercial routes and dissemination of cultures, the nature of its invasion and settlement in Thailand is unclear. Biological invasions occurred both naturally and unnaturally, and the rate of invasions has been elevated since the rise of global trades [1,2,3]. Previous genetic studies using various types of DNA markers showed that B. flabellifer populations have very low genetic diversity [14,15,16,17], and this was concerned as a potential threat to a sustainable use as the species is in decline through extensions of farmland, urbanization and its extremely long juvenile stage
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