Characterization of vegetable cowpea

Abstract

The research project “Characterization of vegetable cowpea (Vigna unguiculata (L.) Walp.)” was conducted at the Department of Olericulture and Department of Plant Biotechnology, College of Agriculture, Vellayani, during 2002 to 2005. The objective of the study was to genetically catalogue the accessions based on IPGRI descriptor for cowpea, to estimate the genetic parameters for different traits in the germplasm as well as to characterize them based on morphological, anatomical, biochemical and molecular parameters. Sixty six accessions of vegetable cowpea collected from various sources upon cataloguing pointed out wide variation for several morphological characters. Analysis of variance revealed significant differences among the accessions for all the characters studied coming under growth, flowering, pod, yield and quality. Among the accessions evaluated, VS 8 (CHCP-1) had the highest yield (1136.89 g) and pods per plant (102.59), while VS 19 (Aryanad, Thiruvananthapuram) and VS 4 (Kanjikuzhi Payar) were noted for their high pod length, pod weight, pod girth, seeds per pod, 100-seed weight and vine length. Root : shoot ratio had the highest phenotypic and genotypic coefficients of variation, followed by pod weight and yield per plant. High heritability coupled with high genetic advance was observed for yield per plant, pods per plant, pod length and pod weight. Correlation studies revealed that characters like vine length, collar girth, pod length, pod girth, pod weight, pods per plant, seeds per pod, 100-seed weight, seed length, seed width, number of harvests, keeping quality and pod protein observed high positive correlation with yield, whereas root : shoot ratio and peduncle length were negatively correlated with yield. Path coefficient analysis indicated that pods per plant exerted the highest positive direct effect on yield, while seed length, pod weight and vine length had high indirect effects on pod yield. In discriminant function analysis, the accession VS 27 (Pattom, Thiruvananthapuram) ranked first, followed by VS 8 (CHCP-1) and VS 19 (Aryanad, Thiruvananthapuram). Based on Mahalanobi’s D2 statistic, the 66 accessions were grouped into ten clusters. Cluster I was the largest containing 18 accessions, while cluster X was the smallest with two accessions. Cluster X performed better most of the biometric characters, with the highest intercluster distance observed between clusters VI and X. On screening the accessions for legume pod borer resistance, VS 19 (Aryanad, Thiruvananthapuram) was found to be the most tolerant, while VS 42 (Pilicode, Kasargode) was the most susceptible. Pod trichome density as well as phenol content were negatively correlated with plant susceptibility index. On the basis of the present study, VS 27, VS 8 and VS 19 were found to be promising based on their superiority in yield, quality and tolerance to legume pod borer and hence they may be utilized for further crop improvement programmes. The organoleptic quality and overall acceptability of all the accessions was also assessed based on appearance / colour, doneness, taste, flavour and texture. The overall acceptability ranged from 2.00 to 3.60 and 2.40 to 3.60 in vegetable and dual purpose / grain types respectively. Characterization of vegetable cowpea based on seed protein banding pattern as well as RAPD revealed the presence of wide variability among the accessions. Similarity coefficient values ranged from 0.20 to 0.97. At 66 per cent similarity, the selected 50 accessions were grouped into eleven clusters. It may be concluded that molecular characterization may be used as a tool for DNA fingerprinting as well as parental selection for further crop improvement in vegetable cowpea. The study also highlighted the probable development of yard long beans from grain type cowpeas with the dual purpose and bush types as intermediate forms.