Rust disease, incited by the fungus Uromyces vignae, adversely affects production and quality of asparagus bean and other types of cowpea in many parts of the world. Genetic resistance to the rust pathogen has been identified in a few accessions, but it is difficult to efficiently transfer the resistance to a broad range of asparagus bean cultivars using traditional breeding approaches. We determined that rust resistance was controlled by a single dominant gene designated Rr1 in the cross of a highly resistant cultivar ZN016 and highly susceptible cultivar Zhijiang 282. Bulked segregant analysis was applied to an F2 population derived from these parents, and an AFLP marker (E-AAG/M-CTG), 150 bp in size, was detected in the resistant bulk. The AFLP fragment was then converted to a SCAR marker, named ABRSAAG/CTG98, and the genetic distance between the marker and the Rr1 gene was estimated to be 5.4 cM. This SCAR marker could be used effectively for MAS of Rr1 in breeding programs to develop rust-resistant asparagus bean cultivars and potentially more widely to breed rust-resistant cultivars of other types of cowpea.
Guojing Li, Yonghua Liu, Jeffrey D. Ehlers, Zhujun Zhu, Xiaohua Wu, Baogeng Wang and Zhongfu Lu
Pei Xu, Tingting Hu, Yuejian Yang, Xiaohua Wu, Baogen Wang, Yonghua Liu, Dehui Qin, Jeffrey Ehlers, Timothy Close, Zhongfu Lu and Guojing Li
Colors of flower and seedcoat are interesting traits of asparagus bean, a cultivated subspecies of cowpea grown throughout Asia for its tender, long green pods. Little is known about the inheritance of these traits including their genome location. We report here the genetic analysis and mapping of the genes governing flower and seedcoat color in asparagus bean based on single nucleotide polymorphism (SNP) and simple sequence repeat (SSR) markers. Analysis of the F1 and F7:8 generation of recombinant inbred lines (RILs) population showed a monogenetic inheritance of both traits. Purple flower and brown seedcoat are dominant over white flower and cream seedcoat, respectively. We further show that genes governing flower color and seedcoat color are tightly linked on LG8, ≈0.4 cM apart. Synteny analysis showed that the gene controlling seedcoat color in our study is syntenic to the soybean T locus. The use of the mapping information in asparagus bean breeding is discussed.