Abstract
Vigna vexillata (L.) A. Rich. (tuber cowpea) is an underutilized crop for consuming its tuber and mature seeds. Wild form of V. vexillata is a pan-tropical perennial herbaceous plant which has been used by local people as a food. Wild V. vexillata has also been considered as useful gene(s) source for V. unguiculata (cowpea), since it was reported to have various resistance gene(s) for insects and diseases of cowpea. To exploit the potential of V. vexillata, an SSR-based linkage map of V. vexillata was developed. A total of 874 SSR markers successfully amplified single DNA fragment in V. vexillata among 1,336 SSR markers developed from Vigna angularis (azuki bean), V. unguiculata and Phaseolus vulgaris (common bean). An F2 population of 300 plants derived from a cross between salt resistant (V1) and susceptible (V5) accessions was used for mapping. A genetic linkage map was constructed using 82 polymorphic SSR markers loci, which could be assigned to 11 linkage groups spanning 511.5 cM in length with a mean distance of 7.2 cM between adjacent markers. To develop higher density molecular linkage map and to confirm SSR markers position in a linkage map, RAD markers were developed and a combined SSR and RAD markers linkage map of V. vexillata was constructed. A total of 559 (84 SSR and 475 RAD) markers loci could be assigned to 11 linkage groups spanning 973.9 cM in length with a mean distance of 1.8 cM between adjacent markers. Linkage and genetic position of all SSR markers in an SSR linkage map were confirmed. When an SSR genetic linkage map of V. vexillata was compared with those of V. radiata and V. unguiculata, it was suggested that the structure of V. vexillata chromosome was considerably differentiated. This map is the first SSR and RAD marker-based V. vexillata linkage map which can be used for the mapping of useful traits.
Highlights
A total of 82 out of 84 polymorphic SSR loci could be assigned to 11 linkage groups (LGs) covering a total length of 510.5 converted into map distances (cM) of the V. vexillata genome at an average marker distance of 7.2 cM (Fig 1, Table 1)
The genetic linkage map developed in this study is the first SSR and RAD markers-based linkage map of V. vexillata
This is the first genetic linkage map consisting of 11 linkage groups that correspond to the haploid chromosome number of V. vexillata (n = 11)
Summary
A domesticated form of V. vexillata, which has large non-dormant seeds and non-shattering pods named “tuber cowpea”, was found cultivated for their flesh tubers and mature seeds in Bali and Timor, Indonesia [2]. The tuberous roots of wild V. vexillata have been eaten like sweet potato by local people in Ethiopia and Sudan [5], in Himalayas and in the hills of eastern and northeastern India at altitude between 1,200 and 1,500m [6,7] and in tropical and subtropical Australia [8]. The wild plant has been used as forage or cover crop in several African countries [9,10] and in Australia [11]
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