Distribution, habitat, morphological diversity and genetic interrelations of native Vigna in the Pilbara, Western Australia

Abstract

A 2-week road trip was made through the Pilbara region to collect seed of native Vigna species. Thirty-two new accessions were collected, all of which were within what can be broadly described as the V. lanceolata Benth. complex. All 32 accessions were amphicarpic, rhizomatous, trailing or vining perennials. The largest and most widely distributed group of 21 accessions belonged to the Silverleaf morphotype and a further nine accessions belonged to the Central morphotype. Two accessions from the Karratha region were of a recently described diminutive species, V. triodiophila. The Silverleaf accessions were all collected from grassy woodlands on river levees and alluvial floodplains. The Central accessions were collected from a more diverse range of habitats, albeit again mostly in wetter or ‘run-on’ parts of the landscape. Measurements of selected traits on a subset of accessions grown for seed increase in Townsville indicated that the Pilbara Silverleaf and Central accessions were comparable with accessions of these morphotypes from elsewhere in northern Australia. Healthy, viable F1 hybrids were readily obtained from crosses between accessions from all three Vigna groups collected from the Pilbara, indicating that all belong to same primary gene pool. This includes V. triodiophila, notwithstanding its taxonomy. Healthy, viable and fertile F1 hybrids were also obtained between the Pilbara accessions of both the Silverleaf and Central morphotypes and respective accessions of these morphotypes from elsewhere in northern Australia. The F1 hybrids between V. triodiophila and both the Silverleaf and the Central accessions exhibited near-normal plant phenotype in terms of the size of their vegetative and reproductive structures, indicating that the diminutive size of V. triodiophila is a recessive trait. The most plausible explanation is that V. triodiophila is a dwarf variant of the Central morphotype, which it most closely resembles apart from its size. The fact that the F1 hybrids between V. triodiophila and two Pilbara Central accessions were fully self-fertile supports that conclusion, while the recovery of dwarf segregants from small numbers of F2 and backcross progeny from one of the crosses indicates that the dwarf trait may involve just a single gene. These 32 new accessions extend the range of climatic and edaphic environments, especially at the harsher end, from which accessions of V. lanceolata have been collected and seeds conserved.