Résumé
New Guinea is considered the most important secondary centre of diversity
for sweet potato (Ipomoea batatas). We analysed nuclear and chloroplast
genetic diversity of 417 New Guinea sweet potato landraces, representing
agro-morphological diversity collected throughout the island, and compared
this diversity with that in tropical America. The molecular data reveal
moderate diversity across all accessions analysed, lower than that found
in tropical America. Nuclear data confirm previous results, suggesting
that New Guinea landraces are principally derived from the Northern
neotropical genepool (Camote and Batata lines, from the Caribbean and
Central America). However, chloroplast data suggest that South American
clones (early Kumara line clones or, more probably, later reintroductions)
were also introduced into New Guinea and then recombined with existing
genotypes. The frequency distribution of pairwise distances between New
Guinea landraces suggests that sexual reproduction, rather than somaclonal
variation, has played a predominant role in the diversification of sweet
potato. The frequent incorporation of plants issued from true seed by
farmers, and the geographical and cultural barriers constraining crop
diffusion in this topographically and linguistically heterogeneous island,
has led to the accumulation of an impressive number of variants. As the
diversification of sweet potato in New Guinea is primarily the result of
farmers’ management of the reproductive biology of their crop, we argue
that on-farm conservation programmes that implement distribution of core
samples (clones representing the useful diversity of the species) and
promote on-farm selection of locally adapted variants may allow local
communities to fashion relatively autonomous strategies for coping with
ongoing global change.