Screening of vegetable cowpea (Vigna unguiculata (L)Walp)germplasm for yield,quality and resistance to collar rot and web blight

Abstract

The present investigation on “Screening of vegetable cowpea (Vigna unguiculata (L) Walp.) germplasm for yield, quality and resistance to collar rot and web blight” was conducted at the Department of Olericulture, College of Agriculture, Vellayani, during the period 2011-2012. The objective of the study was to assess the genetic variability for yield, quality and resistance to collar rot and web blight and elucidating the morphological, anatomical and biochemical basis of collar rot and web blight resistance. The study was conducted in two separate experiments. 1. Evaluation of cowpea accessions for genetic variability, yield, quality and resistance or tolerance to pests and diseases. 2. Screening vegetable cowpea accessions for collar rot and web blight resistance under artificial conditions. In experiment I, 44 accessions of yard long bean and 22 bush cowpea accessions were collected from different parts of country and grown in the field in RBD with three replications as two separate experiments. Analysis of variance revealed that significant difference among the accessions for all the characters studied. Among the accessions, VS 29 (Malappuram local) had the highest yield (1127.52 g) and pods per plant (87.09), while VS 45 was noted that highest pod length, pod girth and pods weight. Correlation studies revealed that characters like primary branches per plant, pods per plant, pod length and pod weight in yard long bean and length and breadth of leaflets, peduncle length, pod length, pod girth and pod weight in bush cowpea observed high positive correlation with yield, whereas peduncle length, days to first harvest and 100 seed weight in yard long bean were negatively correlated with yield. The path coefficient analysis indicated that pods per plant, pod weight, and pod length had direct effect on yield per plant. Phenotypic and genotypic coefficients of variation were high for days to first harvest, pod weight, pod protein and pod borer infestation in yard long bean and in bush cowpea for pod weight, vine length, seeds per pod and pod length while genotypic coefficient of variation was low for days to first flowering in yard long bean and peduncle length in bush cowpea. In yard long bean VS 34 followed by VS 4, VS 29, VS 9 and VS 1 were having the highest selection index values based on discriminant function analysis. VU7, VU 1, VU 14, VU 16 and VU 6 were having the highest selection index values in bush cowpea. On screening the accessions for legume pod borer resistance, VS 44 in yard long bean and VU 24 in bush cowpea were found to be most tolerant, while VS 5 in yard long bean and VU 3 were more susceptible. In field condition, among 44 accession of yard long bean only 12 namely, VS 1, VS 2, VS 9, VS 14, VS 20, VS 21, VS 23, VS 24, VS 29, VS 30, VS 32 and VS 40 were infected with R. solani and shown collar rot symptoms, the remaining accessions were free from collar rot. All the accessions were free from web blight. In bush cowpea, among 22 accessions only four (VU 11, VU 15, VU 17 and VU 19) had shown collar rot symptoms and none of accession showed web blight symptoms. Experiment II was conducted in net house by artificially inoculating the pathogen to all the accessions which were used in experiment I. In screening for collar rot and web blight, the incidence ranged from 0 to 99.81 per cent and 14.32 to 53.78 per cent for collar rot and web blight respectively in yard long bean whereas in bush cowpea collar rot ranged from 0 to 99.64 per cent and web blight ranged from 17.12 to 43.60 per cent. However, 12 accessions of yard long bean viz., VS 6, VS 10, VS 13, VS 18, VS 19, VS 22, VS 32, VS 33, VS 37, VS 38, VS 39 and VS 43 and six accessions of bush cowpea viz., VU 2, VU 5, VU 7, VU 13, VU 16 and VU 18 showed moderately resistance to collar rot and web blight. In both yard long bean and bush cowpea, high positive phenotypic and genotypic coefficient of variation were noticed between collar rot and web blight resistance and proline content phenol content, trichome density, cuticle thickness and number of vascular bundles, while negative correlation was observed with stomatal density. The study revealed that moderately resistant accessions had more number and well developed vascular bundles, high trichome density and cuticle thickness and less stomatal density compare to susceptible ones. High phenol and proline content were responsible for tolerance to collar and web blight resistance. Pod colour was related to collar rot tolerance. Light green and green coloured pods were more susceptible compared with red pod accessions in yard long bean as well as bush cowpea.