Mapping QTLs Associated With Agronomically Important Traits In Asparagus Bean (Vigna. Unguiculata.Ssp.Sesquipedalis)

Cowpea (Vigna. unguiculata L. Walp.) is an important grain legume crop in many parts of the tropics and subtropics. Asparagus bean(Vigna. unguiculata. ssp sesquipedalis), an unique form and subqpecies of cowpea, is a vegetable legume popular in east Asian countries. Flowering Days (FLD), Node of First Flower (NF), Pod Length (PL), P/d Number per plant (PN) and Plant Senescence (PS) are important agronomic traits for asparagus bean, pdaiing crucial roles in detarmining yield and quality of the plants. Exhibiting a consecutive expression of the morphology, all the five traits are considered quantitative traits. Mapping QTLs controlling the five traits and clarifying their inheritance pattern is fundemental to get molecular markers for marker-assisted breeding.Two hundred and nine F8:10 recombinant inbred lines (RILs) produced by the cross of'ZN016'x'Zhijiang282'were used as the mapping population.'ZN016' is a rustic landrace asparagus bean variety while'Zhijiang282' is a commercial asparagus bean cultivar in China. A total of seven replicate experiments were carried out at two location in two year. A total of 21 QTLs were detected using a genetic map constructed from genotyping a 96-line subset of the RIL population with the software MapQTL 5.0. QTLs were found on 9 linkage groups except for LG1 and LG9, of which 5 QTLs were major QTLs.There are 3,4 and 7 QTLs controlling Flowering Days, Node of First Flower and Plant Senescence, respectively. The major QTLs for the 3 traits are co-located on LG11 with the QTL intervals overlapping (10.3cM-42.3cM), and by average explained 27.2%, 22.13% and 22.78% of the phenotypic variation, respectively. Estimated with the two markers (1₀043 and clmO114) closest to the peak of Qfld.zaas-x for FLD, they taken together shortened 3.2% of the fowering days. In four environment, there are respectively 3 markers closest to the peak of QTL for NF and PS,the effect of Clml206,1₁103 and Clml135 decreased 21.7% of the node of first flower by average while the effect of 1₁103,Clml135 and Clm0007 decreased 35.7% of the Plant senescence degree. The 6 minor QTLs controlling PS by average accounted for 8.75% of the phenotypic variance and the minor QTLs for FLD and NF explained about 10%-20% of the phenotypic variance.There are 4 and 3 QTLs controlling PL and PN, respectively. The intervals of major QTLs for the two traits were overlapped on LG3, and the two QTLs explained 44% and 20.5% of the phenotypic variation, respectively. The marker 1₀247 and clm0614 was co-located with the peak of QTL for PL and PN respectively, which increased up to 21% of the PL and 21.2% of the PN, respectively. Qpl.zaas-2 for PL and Qpn.zaas-PN were mapped coincidently onto the same interval on LG2, with the marker (Clm0089) closest to QTL peak being identical. The average percentage of phenotypic variation they explained was 12% and 13.2%, respectively. Qpl.zaas-5 and Qpl.zaas-10 explained 44% and 20.5% of the phenotypic variation, respectively. Two minor QTLs for PN (Qpn.zaas-4 and Qpn.zaas-7) both explained about 10% of the phenotypic variation.Through functional analysis of makers, we found that the SNP marker 1₀371 which co-located with the peak of Qpl.zaas-2, was derived from an EST with the annotation of CYCD3 (Cyclin D3) protein kinase. Given the known function of CYCD3 in regulating cell elongation, cell expasnison and cytokinin signaling, this gene was considered a strong candidate gene for the trait of PL. Based on cowpea-soybean synteny, we also found a LOB (Lateral Organ Boundary) domain protein gene and CYCD3 as candidate gene for the trait of PL and PN respectively.In summary, we detected the QTLs controlling FLD, NF, PL, PN, PS and explored candidate gene for the trait of PL and PN, which provides a solid basis for marker-assisted breeding of these important triats in asparagus bean.