Genome dissection of traits related to domestication in azuki bean (Vigna angularis) and comparison with other warm-season legumes.

BACKGROUND: The objective of this study was to dissect into quantitative trait loci (QTLs) the large morphological and physiological differences between cultivated azuki bean (Vigna angularis) and a wild relative and to infer the commonalities of the QTLs for domestication-related traits across the Asian Vigna and with other warm-season legumes.

METHODS: Two linkage maps, for the BC(1)F(1) and F(2) populations, respectively, from the same cross between azuki bean and V. nepalensis were developed. Using these linkage maps QTLs for 33 domestication-related traits were analysed and mapped. The location of mapped QTLs was compared with locations of similar QTLs in other warm-season legumes.

KEY RESULTS: QTLs were detected for seed-, pod-, stem- and leaf-related traits. Most traits were controlled by between two and nine QTLs but several traits, such as pod dehiscence, were controlled by single genes. QTLs for domestication-related traits were restricted to particular regions of the azuki bean genome, especially linkage groups 1, 2, 4, 7 and 9. Linkage groups 1 and 2 had QTLs for a suite of traits including pod size, germination, seed size and lower stem length. QTLs on linkage groups 7 and 9 were associated with upper stem length, maximum leaf size and pod and seed size. Pleiotropy or close linkage of genes for domestication-related traits is suggested in these regions. While some QTLs are common to azuki bean and other warm-season legumes, many are recorded for the first time in azuki bean.

CONCLUSIONS: QTLs for a large number of domestication-related traits have been mapped for the first time in azuki bean. QTLs with unexpected effect and new QTLs for traits such as seed size have been found. The results provide a foundation that will be useful for improvement of azuki bean and related legumes.