Farmer Selection and Conservation of Crop Varieties

After domestication, plant species were often transported widely, and many genetically distinct farmers’ varieties (FVs, crop varieties traditionally maintained and grown by farmers) developed in specific locations. FVs continue to be grown today by many small-scale farmers in traditionally-based agricultural systems (TBAS), fulfilling both local or regional consumption needs, as well as the larger social need for the conservation of genetic diversity. Crop genetic variation (VG) is a measure of the number of alleles and degree of difference between them, and their arrangement in plants and populations. A change in VG over generations is evolution, though one form of this change, microevolution, is reversible. Farmers and the biophysical environment select plants within populations. Farmers also choose between populations or varieties. This phenotypic selection and choice together determine the degree to which varieties change between generations, evolve over generations, or stay the same. Conservation in a narrow sense means the preservation of the VG present at a given time. However, in situ conservation in farmers’ fields is commonly understood to mean that the specific alleles and genetic structures contributing to that VG may evolve in response to changing local selection pressures, while still maintaining a high level of VG. [3] In contrast, ex situ conservation in genebanks attempts to conserve genetic diversity present at a given location and moment in time, preserving the same alleles and structures over time. Thus, different forms of conservation include different amounts and forms of change. Sometimes farmers carry out selection or choice intentionally to change or conserve VG. However, much of farmer practice is intended to further production and consumption goals and affects crop evolution unintentionally. Therefore, in order to understand farmer selection and conservation, it is important to understand the relationship 1) between production, consumption, selection, and conservation in TBAS, and 2) between farmer knowledge and practice and the basic genetics of crop populations and their interactions with growing environments [genetic variation, environmental variation and genotype-by-environment interaction (G E), and response to selection] (Table 1).