Genetics of Brassica rapa L.

Abstract

Brassica rapa (2n = 20, AA) is one among the six economically important cultivated Brassica species of U’s triangle. The presence of wide genetic and morphological diversity in the form of several subspecies in different geographical regions allows growing of this species for producing leafy vegetables, vegetable oils, turnips roots, turnip greens, turnip tops, and fodder turnip. In addition, it is one of the diploid progenitor parental species which contributed A genome to the important oilseed crops, Brassica juncea (2n = 36, AABB) and Brassica napus (2n = 38, AACC). Due to the presence of wide genetic variability, genetic analysis for important traits and improvement in this crop are possible. While conventional genetic analyses and breeding could achieve success in improvement of many traits, but for the majority of the agronomically important traits recent advances in genetic marker techniques supplemented heavily for this crop. Molecular markers have been used to analyze genetic diversity in B. rapa, mapping of different traits in the genome in segregating populations generated for investigations of specific traits of interest. Several mapping studies have led to the identification and tagging of many traits for marker-assisted breeding, and in some cases map-based cloning of the responsible genes have been done, e.g. the flowering time gene FLC. However, traditional mapping of quantitative trait loci (QTL) is often not sufficient to develop effective markers for trait introgression or for identification of the genes responsible. The ongoing sequencing work of B. rapa genome will undoubtedly give great insight into the genetics underlying both simple and complex traits in this crop. Comparative mapping with the closest relative Arabidopsis thaliana and identification of candidate genes, use of EST-derived SSRs and SNPs from Arabidopsis and other Brassica species for high density mapping, isolation, and development of gene-based functional molecular markers would also be very much helpful for this crop. This chapter reviews the current use of available molecular marker technologies in B. rapa genetic analysis and breeding for important morphological, agronomic, quality, abiotic and disease resistance QTL/gene mapping and their utilization in marker-assisted breeding.