Characterisation and systematic evaluation of genetic resources of the genus Vigna

Abstract

Vigna belonging to the family Leguminoseae is a large genus comprising of seven sub-genera and over 150 species. The two sub-genera Vigna and Ceratotropis contain the most important cultivated species. The taxonomical identification of many of these species is still confusing. The closely related wild species serve as a source of many desirable genes that can be utilised in the interspecific hybridisation programmes. This is possible only when the relationships among the different Vigna species are well understood. In this context, the present study “Characterisation and systematic evaluation of genetic resources of the genus Vigna” was undertaken in the Department of Plant Breeding and Genetics, College of Horticulture at Vellanikkara. Investigations were undertaken to characterise the accessions of Vigna germplasm available at National Bureau of Plant Genetic Resources (NBPGR) Regional Station, Vellanikkara, Thrissur using morphological markers and to confirm the results using biochemical and molecular markers in distinct variants belonging to different taxa as well as to prepare a key for the identification of different Vigna taxa. The 150 accessions available at NBPGR Regional Station, Vellanikkara were subjected to morphological, biochemical and molecular characterisation. For morphological characterisation 48 qualitative and 24 quantitative characters were taken. The biochemical characterisation of the selected distinct variants from each taxa was done by isozymes, peroxidase and poly-phenol oxidase. The molecular characterisation was done with Inter Sequence Repeat Analysis using 10 different primers. The clustering patterns based on all three characterisation were compared and key for identification of different taxa of Vigna was developed. Among the qualitative characters evaluated, type of seed germination, nature of attachment of primary leaves, size of stipule, shape of stipule, presence of ligule, shape of bracteole, nature of pod attachment to peduncle, curvature of pod, shape of seed and shape of hilum were distinct for each taxa. Variability was observed in size and shape of stipules and bracteoles. Based on the qualitative characters the 150 accessions were reclassified into 22 taxa. One accession originally classified as V.radiata var.sublobata was found to be distinct taxa of Vigna and hence regrouped as distinct taxa. All the 24 quantitative characters studied exhibited wide range of variability. The keel pocket was present in all taxa except V.unguiculata, V.marina and V.pilosa. The length of keel pocket also varied from taxa to taxa. Cluster analysis based on qualitative, quantitative, biochemical and molecular characters resulted in 10, 5, 4 and 12 clusters respectively. A statistical methodology was worked out to compare the parallelism among the different clustering patterns. The result showed that there existed a similarity between clusters formed based on quantitative and qualitative characters, with majority of accessions of each taxa in a qualitative cluster falling in the same quantitative cluster. The accessions taken for isozyme and molecular study were distinct. Accessions of same taxa which fell in same clusters based on isozyme and molecular markers fell in different clusters based on quantitative characters and vice-versa, indicating the differences and similarities among these accessions at isozyme and molecular level. Key quantitative characters were also identified for each taxa based on weighted average. Based on morphological, biochemical and molecular characters, a dichotomous key was developed to identify different taxa. The key that is now proposed is different from the existing one which is based on floral and fruit characters alone.