Gene Pool Review Articles

For many cultivated species, genetic uniformity is the result of modern breeding and breeding practices. Common wheat (Triticum aestivum L.) is an exception, having been a genetically narrow species throughout its existence. This article discusses the evolutionary bottlenecks by which the germplasm of today's wheat has descended, and the ways in which the genetic makeup of wheat is enriched with genes from other species. The global common wheat gene pool comes from a very small number of spontaneous interspecific hybrids, which arise from two natural amphiploidization events. In a more recent event, one or more emmer wheat plants, which were cultivated at the time by the early Neolithic cultivators, were fertilized by a weed diploid goat, Aegilops tauschii, producing primitive common wheat. Due to the rarity of this event, today's common wheat has extremely low levels of polymorphism to enzymes, storage proteins and DNA marker loci, compared to its parent species, especially Ae. tauschii. In fact, most of the evolutionary evidence suggests that common wheat began its existence as a highly monomorphic species and that its genetic variation was further reduced by domestication. Despite the narrow genetic base of common wheat, human-guided evolution has produced a profusion of distinct land races over a period of five millennia or more, and modern farming has maintained constant genetic improvement throughout the century in progress. To protect these gains, humans have used interspecific crosses to improve the resistance of wheat pests. But why should the progenitors of wheat not be considered sources of genetic variation useful for all economic traits, says that humans would have been fortunate if the rare amphiploids that gave birth to common wheat carried the ideal allele to each locus. They therefore provide a critical analysis of the methodologies allowing to circumvent the genetic bottleneck of wheat and to deepen its main genetic pool. It emphasizes two general approaches to expanding the genetic makeup of wheat: amphiploidization and direct backcrossing.