Association mapping to dissect and exploit existing natural variation for crop improvement

The germplasm is often exploited to develop improved crop varieties for changing needs and environments. The vast amount of genetic variation present in the germplasm can be exploited to the best when the economically important traits have been mapped with molecular markers using specially designed mapping populations. Most of yield contributing traits are controlled by many loci and their molecular characterization and genetic mapping is called quantitative trait loci mapping (QTL-mapping). However, it is always not possible or convenient to construct such mapping populations in all crop plants. For example, in many tree species, pure lines or inbred lines, it is difficult if not impossible to construct mapping populations. Under such situations and in order to achieve higher level of resolution and precision in QTL analysis the association mapping technique is used. In the present review, we define and distinguished between linkage analysis based mapping association mapping and linkage disequilibrium (LD) mapping, and then described the technique of association mapping used to dissect the genetic basis of complex traits for crop improvement. This paper will be a key reference for the beginners and research scholars who are involved in association mapping in crop plants.