Genotypic variation in domesticated and wild accessions of the tropical tuberous legume Vigna vexillata (L.) A. Rich.

Abstract

Vigna vexillata is an underutilised perennial tuberous legume with several multipurpose uses. In a comparative study to identify sources of potentially useful genetic variation, six cultivated accessions from two regions in Bali, a var. macrosperma accession and 12 wild accessions from Africa, Australia and Indonesia were evaluated for selected morphological, agronomic and phenological traits. Measurements were made of qualitative and quantitative traits on plants grown over the spring–autumn period in large pots on benches outdoors at Townsville, Australia (19°19.7′S, 146°45.7′E). Variation among the genotypes was assessed between the three main groups of accessions, between provenances within groups, and between accessions within provenances. Large variation was observed for most traits, with clear differentiation evident between the three main groups of accession. There was minimal variation within the Bali accessions for all except tuber attributes, while within the wild accessions there were some small differences due to provenance. The Bali accessions and var. macrosperma shared many attributes often associated with domestication, distinguishing them from the wild accessions. For example, the Bali accessions and var. macrosperma had broad-ovate leaflets, uniform-coloured seed testa, and non-dehiscent pods, and larger pods and seeds, seed yield per plant and seed harvest index than the wild accessions. Nonetheless, there were distinct differences between the Bali accessions and var. macrosperma. The Bali accessions had a larger seed size but fewer seeds per pod than var. macrosperma and were unique in having more than twice as many flowers per peduncle and a much longer duration of seed development than either var. macrosperma or the wild accessions. Whereas the Bali accessions were photoperiod-sensitive and as a consequence, late flowering and vegetatively vigorous, var. macrosperma was early flowering, more bush-like in habit and had higher seed yield and seed harvest index, all traits associated with domestication. Across all the accessions, there were significant correlations between many pairs of traits. While the present study identified sources of potentially useful variation, it was concluded that the lack of variation within the Bali accessions, combined with the paucity of both cultivated and var. macrosperma accessions in current germplasm collections, pose constraints to the future genetic improvement of V. vexillata.