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.