Evalution of dolichos bean (Lablab purpureus (L.) sweet) accession (Pole type) for yield and quality

Abstract

Dolichos bean (Lablab purpureus (L.) Sweet) is a multi-purpose crop cultivated in both tropical and sub-tropical conditions. The tender pods rich in protein, fibre, iron and calcium are used as vegetable and dried seeds as pulse. Tender leaves are cooked and consumed as vegetable. The pole types are photosensitive in nature preferring short days and comparatively cool season for flowering. Despite of its multi-utility and multiple benefits, its cultivation is done in limited area only. Thus, there is a huge scope to expand cultivation to non-conventional regions which would assure nutritional and income security for the farmers. The efforts for genetic enhancement of this crop also has been limited. In this context, the present study was undertaken with the objectives of determining the genetic variability, genetic divergence and character associations among dolichos bean accessions for yield and yield contributing traits and to evaluate the accessions for quality. The experiment was conducted at the Department of Vegetable Science, College of Horticulture, Vellanikkara during September 2019- April 2020. The dolichos bean accessions were catalogued as per the NBPGR Minimal Descriptor for Characterization and Evaluation of Agri-Horticultural crops (2000). The flower colour varied from white to purple. The pod colour varied from light green, green to purple. Green pods with purple border were observed in LP-2, LP-12, LP-19, LP-31, LP-32 and LP-35. Purple pods were observed in LP-11, LP-17 and LP-22. The pod shape varied from straight, intermediate to curved. Based on the reaction to bacterial wilt disease, the accessions were categorized into susceptible and resistant. The accessions, LP-1, LP-5, LP-6, LP-9 and LP-14 were highly susceptible and showed 100 per cent bacterial wilt incidence. The analysis of variance of the 25 accessions showed significant differences among them for all traits under study. Genetic parameters like GCV, PCV, heritability, GA and GAM were estimated to study the nature and extent of variability. High GCV, PCV, heritability and GAM were exhibited by the characters green pod yield/plant, number of seeds/pod, pod length, pod girth, pod weight, number of pods/plant and total phenols which indicated the presence of high variability and additive gene action for these traits. Hence, these traits can be improved through selection. Quality traits viz., iron, calcium, total phenols, and phytic acid exhibited close association between PCV and GCV. In addition, moderate to high heritability and GAM were observed indicating that phenotypic values were a true measure of the genotype and the improvement of these traits is possible through selection. Green pod yield per plant was significantly, positively correlated with number of pods per plant, number of harvests, duration of the crop, calcium and crude protein. Further, green pod yield per plant was positively correlated with number of pods per cluster, pod length, pod weight and pod girth. However, these correlations were not significant which indicated their independent nature with respect to yield. Path coefficient analysis of yield and its component characters revealed that the highest direct positive effect on green pod yield per plant was exhibited by number of pods per plant followed by days to first flowering, pod weight, number of seeds per pod and duration of the crop. Hence direct selection of accessions based on these traits would improve yield. From the present study, accessions viz., LP-2, LP-13 and LP-34 could be selected as promising ones based on these traits. Twenty five accessions of dolichos bean were grouped into six clusters based on D2 values. Cluster VI had highest number of accessions (8) followed by cluster III (6). Cluster I and II had four accessions each. There were two accessions in cluster IV and one accession in cluster V. Inter cluster distance was maximum between cluster IV and cluster V. Hence, superior hybrids could be obtained by hybridization among the accessions present in these clusters. Sensory evaluation was conducted in the cooked pods to score the accessions based on their appearance, colour, flavour, texture, taste and overall acceptability. LP- 31, LP-28 and LP-13 were superior in sensory qualities. The selection criteria for dolichos bean was fixed by taking the characters such as green pod yield per plant, number of pods per plant, pod weight, days to first flowering and overall acceptability of sensory evaluation and the accessions LP-28, LP- 13, LP-12, LP-2 and LP-35 were identified as the most promising ones based on this.