Résumé
We analyzed a representative collection of New World sweet potato
landraces (329 accessions from Mexico to Peru) with both chloroplast and
nuclear microsatellite markers. Both kinds of markers supported the
existence of two geographically restricted genepools, corresponding to
accessions from the north-western part of South America and accessions
from the Caribbean and Central America super-region. Our conservative
cpSSRs markers revealed that the divergence between the two haplotype
groups is associated with numerous mutation events concerning various
markers, supporting the idea that this divergence may be ancient,
predating domestication. For both kind of markers, we found no significant
difference in diversity between the two genepools and detected
region-specific alleles in both groups. Previous studies have favoured the
hypothesis of a single domestication of this crop. Our analysis suggests
at least two independent domestications, in Meso-America and in the
north-western part of South America. Sweet potato was then dispersed from
these centres throughout tropical America. Comparison of nuclear and
chloroplast data suggests that exchanges of clones and sexual reproduction
were both important processes in landrace diversification in this clonally
propagated crop. Our analysis provides useful tools for rationalizing the
conservation and use of germplasm collections.