Do farmers reduce genetic diversity when they domesticate tropical trees? A case study from Amazonia.

Agroforestry ecosystems may be an important resource for conservation and sustainable use of tropical trees, but little is known of the genetic diversity they contain. Inga edulis, a widespread indigenous fruit tree in South America, is used as a model to assess the maintenance of genetic diversity in five planted vs. five natural stands in the Peruvian Amazon. Analysis of five SSR (simple sequence repeat) loci indicated lower allelic variation in planted stands [mean corrected allelic richness 31.3 (planted) and 39.3 (natural), P = 0.009]. Concerns regarding genetic erosion in planted Amazonian tree stands appear valid, although allelic variation on-farm is still relatively high.

Genetic differentiation and trade among populations of peach palm ( Bactris gasipaes Kunth) in the Peruvian Amazon-implications for genetic resource management.

Peach palm ( Bactris gasipaes Kunth) is cultivated for fruit and 'heart of palm', and is an important component of agroforestry systems in the Peruvian Amazon. In this study, AFLP was used to compare genetic diversity among domesticated populations along the Paranapura and Cuiparillo rivers, which are managed by indigenous and colonist farming communities, respectively. Gene diversity was 0.2629 for the populations in indigenous communities and 0.2534 in colonist communities. Genetic differentiation among populations ( G(st)) was 0.0377-0.0416 ( P<0.01) among populations along both rivers. There was no relation between genetic differentiation and the geographical location of populations along the rivers. Since natural seed dispersal by birds and rodents is thought to occur only across relatively short distances (100-200 m), it is likely that exchange of material by farmers and commercial traders is responsible for most of the 'long-distance' (over more than 20 km) gene flow among populations along the two rivers studied. This exchange of material may be important to counteract the effects of selection as well as genetic drift in small groups of trees in farmers' fields, much as in a metapopulation, and may account for the weak genetic differentiation between the two rivers ( G(st)=0.0249, P<0.01). A comparison with samples from other landraces in Peru and Brazil showed the existence of an isolation-by-distance structure up to 3,000 km, consistent with gene flow on a regional scale, likely mediated by trade in the Amazon Basin. Results are discussed with regard to practical implications for the management of genetic resources with farming communities.