Soleri, D. and D.A. Cleveland (2004) Farmer selection and conservation of crops. In the section "Crop Evolution and Domestication", P. Gepts, editor, in Encyclopedia of Plant & Crop Science, R.M. Goodman, editor, pp. 433-438. New York: Marcel Dekker, Inc.

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ABSTRACT
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. In contrast, ex situ conservation in genebanks attempts to conserve VG 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 between production, consumption, selection and conservation in TBAS, and between farmer knowledge and practice and the basic genetics of crop populations and their interactions with growing environments.

Selection and conservation in TBAS contrast substantially with industrial agricultural systems, and understanding farmers' practices, and the knowledge and goals underlying them, is critical for supporting food production, food consumption, crop improvement, and crop genetic resources conservation for farm communities in TBAS and for long-term global food security. The urgency of understanding farmer selection and conservation will increase in the future with the on-going loss of genetic resources, the rapid spread of transgenic crop varieties with limited genetic diversity, the development of a global system of intellectual property rights in crop genetic resources, and the movement to make formal plant breeding more relevant to farmers in TBAS through plant breeding and conservation based on direct farmer and scientist collaboration.

(View introduction at http://www.dekker.com/sdek/15072934-73756523/abstract~db=enc~content=a713575966 )