Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: November 29, 2007
Publication Date: November 29, 2007
Citation: Jaradat, A.A. 2007. The genetic structure of wheat landraces and the challenge to conserve them on the farm [abstract]. Restoring Ancient Wheat. p. 5. Technical Abstract: Indigenous farming communities in the Fertile Crescent (FC) contributed for millennia to the evolution, enrichment and on-farm conservation of wheat landraces (LR). The traditional cultures and cropping systems of the FC shaped present genetic structure and determined the changes within LR populations. Wheat LRs are complex, variable and genetically dynamic and diverse populations in equilibrium with both environment and pathogens. In the FC, wheat LRs have undergone strong selection pressures throughout their evolutionary history, and developed multilocus structures as a result of selection, genetic drift or fragmentation of their populations; these structures are retained through selection, isolation and the lack of migration, and restrictions on outcrossing and genetic recombination. Little has been done to understand the genetic structure of LRs and the interspecific diversity in the subsistence agricultural eco-systems they dominate. The genetic structure of LRs is considered as an evolutionary approach to survival and performance, especially under the arid and semi-arid conditions of the FC. The combined effects of natural and artificial selection have led to an architecture of genotypes representing different combinations of traits such as growth habit, cold, heat or drought tolerance, early growth vigor, time to heading and maturity and quality traits. The complexity of the population structure of wheat LRs may arise from the number of different homozygotes and the occurrence and frequency of heterozygotes in populations. Characterization of the population structure of LRs is critical to identify and correctly interpret the association between their functional and molecular diversity. Such information is essential to define the areas of adaptation of different LRs, to identify priority areas for on-farm conservation, and to understand the genetic consequences of the interaction between growing environments and farmers’ practices. Two sets of attributes are essential to understanding the genetic structure of LRs: (1) marker diversity or the extent of differences between individual copies of a gene and (2) the variation in adaptation. The first is informative as to the ancestry or breeding history of the populations and also considered an indicator of the recency of bottlenecks in population size, the prevalence of outcrossing, the ease with which genes are recombined, and the level of gene flow between LR populations. The second set comprises indicators of the degree to which populations are adapted to the biotic and abiotic aspects of the environment and of their potential for continued performance or as donors of traits in wheat breeding. The main challenges of on-farm conservation of wheat LRs in the FC are non-biological, but rather a complex of ethno-anthropological processes, involving legal, economic and social factors superimposed on ecological and genetic processes.