Abstract
Widespread adoption of new varieties can be valuable, especially where improved agricultural production technologies are hard to access. However, as farmers adopt new varieties, in situ population structure and genetic diversity of their seed holdings can change drastically. Consequences of adoption are still poorly understood due to a lack of crop genetic diversity assessments and detailed surveys of farmers' seed management practices. Common bean (Phaseolus vulgaris) is an excellent model for these types of studies, as it has a long history of cultivation among smallholder farmers, exhibits eco-geographic patterns of diversity (e.g., Andean vs. Mesoamerican gene-pools), and has been subjected to post-Columbian dispersal and recent introduction of improved cultivars. The Hoima district of western Uganda additionally provides an excellent social setting for evaluating consequences of adoption because access to improved varieties has varied across farmer groups in this production region. This study establishes a baseline understanding of the common bean diversity found among household producers in Uganda and compares the crop population structure, diversity and consequences of adoption of household producers with different adoption practices. Molecular diversity analysis, based on 4,955 single nucleotide polymorphism (SNP) markers, evaluated a total of 1,156 seed samples that included 196 household samples collected from household producers in the Hoima district, 19 breeder-selected varieties used in participatory breeding activities that had taken place prior to the study in the region, and a global bean germplasm collection. Households that had participated in regional participatory breeding efforts were more likely to adopt new varieties and, consequently, diversify their seed stocks than those that had not participated. Of the three farmer groups that participated in breeding efforts, households from the farmer group with the longest history of bean production were more likely to conserve “Seed Engufu”, a local “Calima”-type variety of the Andean bean gene pool, and, at the same time, introduce rare Mesoamerican gene pool varieties into household seed stocks.
Highlights
Varietal adoption and ongoing selection under agronomic and social pressures represent two major processes that shape in situ crop genetic diversity and the generation and maintenance of distinct “landraces” (Zizumbo-Villarreal et al, 2005; Worthington et al, 2012; Pautasso et al, 2013; Soleri et al, 2013)
The analysis draws from household survey data and seed stock molecular data that span diverse groups of common bean (Phaseolus vulgaris)producing households to better understand how these processes can vary across social settings
The Mesoamerican gene pool was further subdivided in two clusters along PC2 (14%) representing two distinct races: Durango-Jalisco and Mesoamerican
Summary
Varietal adoption and ongoing selection under agronomic and social pressures represent two major processes that shape in situ crop genetic diversity and the generation and maintenance of distinct “landraces” (Zizumbo-Villarreal et al, 2005; Worthington et al, 2012; Pautasso et al, 2013; Soleri et al, 2013). The objective of the study is to primarily describe farmers’ seed stocks in relation to breeder-selected varieties found within country and the global bean reference collection. This analysis supports the second objective, namely to understand the effects of seed sources and early-stage adoption on seed stock population structure and genetic diversity. PVS-trial varieties that were evaluated by breeding program-affiliated households did not show high levels of genetic relatedness to Seed Engufu. K20 and K 132 were the most morphologically similar to Seed Engufu of all the varieties included in the PVS-trials Both varieties are Calima-type improved material that were released and disseminated with widespread adoption in Uganda over the last three decades (Table 1). The Uganda National Bean Program released K 132, a Calima seed type similar to K20
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