Effect of the management of seed flows and mode of propagation on the genetic diversity in an Andean farming system: the case of oca (Oxalis tuberosa Mol.)

The seed system is a major component of traditional management of crop genetic diversity in developing countries. Seed flows are an important part of this system. They have been poorly studied for minor Andean crops, especially those that are propagated vegetatively. We examine the seed exchanges of Oxalis tuberosa Mol. (oca), a vegetatively propagated crop capable of sexual reproduction. We studied the seed exchanges of four rural communities in Candelaria district (Cochabamba department, Bolivia) at the international and local levels, emphasizing the spread of new sexually-produced genotypes through these exchanges. Interviews with 44 farmers generated socioeconomic, agronomic, crop diversity and seed exchange information, and data on the potential incorporation of new sexually-produced genotypes in the crop germplasm. We interviewed merchants to evaluate the input and output of genetic diversity in the communities studied. Results showed a positive effect of the farmers’ wealth on the diversity cultivated and on seed exchanges. Most seed exchanges occurred at market, creating a distinction between cash and self-consumption landraces. Cash landraces were intensively exchanged; self-consumption landraces were isolated at the farmer level and prone to genetic drift and complete loss. Merchants exported seeds of cash landraces across Bolivia and into Peru and Argentina. New sexually produced genotypes are less incorporated into cash landraces than in self-consumed landraces. However, new genotypes incorporated into cash landraces are diffused faster and better, being more intensively exchanged. We propose conservation strategies that can be applied to other vegetatively propagated and minor Andean crops.