Genetic analysis and molecular mapping of genes controlling seed coat colour in adzuki bean (Vigna angularis)

Abstract

Seed coat colour is an important agronomic trait in adzuki bean (Vigna angularis). Here, we identified four genes controlling seed coat colour in this species. We conducted a quantitative trait locus (QTL) study of 133 recombinant inbred lines (F₆) derived from a cross between V. angularis Shumari (red) and landrace Acc2265 (olive buff), by using simple sequence repeat (SSR) markers. We identified a strong QTL, designated OLB1, which explained 54, 43, and 56 % of the total variance in the L* (lightness), a* (redness), and b* (yellowness) values, respectively. In addition, we identified a minor QTL, designated OLB2, which explained 6 % of the total variance in redness. OLB1 and OLB2 were located on linkage group (LG) 1, >80 cM apart. The F₁ phenotype was olive buff, implying that the red colour trait was recessive. Next, we crossed two spontaneous mutants, ‘Shiro-shouzu’ (ivory yellow) and ‘TA230002’ (pale olive buff), to the red-seeded ‘Beni-shouzu’. Genetic analysis of the F₁, F₂, and F₃ progenies derived from each parental cross revealed that the ivory yellow and pale olive buff traits were recessive to the red trait. Molecular mapping studies indicated that the ivory yellow trait was controlled by a single Mendelian gene, designated IVY, located on LG 8. The pale olive buff trait was also controlled by a single Mendelian gene, designated POB, located on LG 10. Our findings will facilitate the development of novel red seed cultivars and the introgression of ivory yellow genes into desirable cultivars, via marker-assisted selection.