Co-localization of QTLs for pod fiber content and pod shattering in F2 and backcross populations between yardlong bean and wild cowpea

Yardlong bean [Vigna unguiculata (L.) Walp. ssp. unguiculata cv.-gr. sesquipedalis] is a vegetable legume crop evolved from cultivated grain cowpea (V. unguiculata ssp. unguiculata cv.-gr. unguiculata) which is domesticated from wild cowpea. It has a dramatic change in pod length and pod fiber content, and a complete loss of pod shattering, as compared to its wild progenitor. In this study, we identified quantitative trait loci (QTLs) controlling pod fiber content and pod shattering in two populations (BC1F1 and F-2) derived from a cross between yardlong bean and wild cowpea. BC1F1:2 and F-2:3 families were grown under field condition in which insoluble dietary fiber (cellulose, hemicelluloses and lignin) contents in mature pods, and pod shattering were evaluated. Correlation analysis showed positive relationship among the types of fiber, and between the fiber and shattering. Inclusive composite interval mapping revealed that a major QTL on linkage group 7 (LG7) controlled cellulose, hemicellulose and lignin contents in pod, and pod shattering. The other QTLs related to pod fibers on LG1 and LG4 also co-localized with the QTLs for pod shattering. Comparative genome analysis with azuki bean (Vigna angularis) suggested that the QTL region on LG7 for cellulose, hemiclellulose, lignin and pod shattering in yardlong bean contains genes encoding MYB transcription factor, MYB83, regulating biosynthesis of the three fibers, while the QTL region for cellulose and shattering of pod on LG1 harbors gene encoding cellulose synthase A7 (CESA7). These genes may be important targets for functional study to reveal major factors regulating pod fiber biosynthesis and pod shattering in yardlong bean.