Linkage disequilibrium, genetic association mapping and gene localization in crop plants

DNA-based molecular markers have been extensively utilized for a variety of studies in both plant and animal systems. One of the major uses of these markers is the construction of genome-wide molecular maps and the genetic analysis of simple and complex traits. However, these studies are generally based on linkage analysis in mapping populations, thus placing serious limitations in using molecular markers for genetic analysis in a variety of plant populations. Therefore, alternative approach has been suggested, linkage disequilibrium-based association analysis which detects and locates quantitative trait loci (QTL) by the strength of the correlation between a trait and a marker. Although association analysis has already been used for studies on genetics of complex traits in humans, its use in plants has newly started. In the present review, we describe what is known about variation in linkage disequilibrium (LD) and summarize published results on association studies in crop plant species. We give a list of different factors affecting LD, and discuss the current issues of LD research in plants. Later, we also describe the various uses of LD in crop plants research and summarize the present status of LD researches in different plant genomes. Finally, future key issues about the application of these studies on the localization of genes in these crop plants have been also discussed.