Wild relatives and crop cultivars: detecting natural introgression and farmer selection of new genetic combinations in agroecosystems

Whether new combinations of genes that result from hybridization and introg ression between wild and cultivated taxa are maintained, with the resultant development of populations with new characteristics, depends on natural se lection, and in the case of crops, on human selection. While many cases of deliberate introgression of desirable traits into crop cultivars as part of breeding programmes are known, the extent and significance of natural or f armer-assisted introgression is uncertain. A range of techniques have been used to document natural hybridization and introgression of agricultural cr ops and their wild relatives in many crops including maize, wheat, barley, oats, pearl millet, foxtail millet, quinoa, hops, hemp, potato, cocona, cas ava, common bean, cowpea, pigeon pea, carrots, squash, tomato, radish, letu ce, chilli, beets, sunflower, cabbage, and rasberries. However, the majorit y of these studies are based on morphological characters, and few have inve stigated the frequency with which such new types are produced and retained in natural and agroecosystems for farmer selection. Even more limited is in formation on the role of farmers in recognizing and selecting new genetic v ariation from the natural introgression of crops with their wild relatives, and the impact, once selected, of these new genetic combinations on the cr op diversity. Molecular evaluation of natural introgression linked to inves tigations of farmer recognition and use of introgressed types provide ways of evaluating whether farmer selection for introgressed types is a signific ant process in increasing the genetic diversity of crop plants.