Genetic and Molecular Variability, Character Association and Diversity Analysis in Cowpea (Vigna unguiculata (L.) Walp.)
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Date
2015-07
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jau,junagdh
Abstract
An investigation was carried out using 56 genotypes of vegetable cowpea to measure the genetic and molecular variability, correlation coefficients, path coefficients, genetic divergence and also to construct the selection indices. The material was evaluated in a randomized block design with three replications at the Instructional Farm, JAU, Junagadh during Kharif 2014. The molecular variability was determined at the Department of Biotechnology, JAU, Junagadh.
Analysis of variance revealed significant differences among the genotypes for all the 12 characters studied. Coefficient of range was observed highest for green pod yield per plant followed by number of pods per plant, ten pod weight and number of pods per cluster. The highest genotypic coefficient of variation was observed for number of pods per plant followed by green pod yield per plant, ten pod weight, number of pods per cluster and hundred fresh seeds weight. High heritability were observed for hundred seed weight, ten pod weight, number of primary branches per plant, number of pods per plant and plant height. High expected genetic advance was found for green pod yield per plant.
The values of genotypic correlation were higher than their corresponding phenotypic correlations. Green pod yield per plant was found to be significantly and positively correlated with pod length, ten pod weight and number of pods per plant at both genotypic and phenotypic levels. The path coefficient analysis showed that number of pods per plant, pod length and ten pod weight exhibited high and positive direct effects on green pod yield per plant. Whereas, number of pods per cluster showed moderate and positive direct effect on green pod yield per plant
A total of 15 selection indices were constructed involving cowpea green pod yield and three yield components using the discriminant function technique. The efficiency of selection increased with the inclusion of more number of characters in
the index. Selection index involving green pod yield per plant, number of pods per plant, pod length and ten pod weight could be advantageously exploited in the vegetable cowpea breeding.
The 56 genotypes were grouped into 10 clusters by Mahalanobis’s D2-statistic. The clustering pattern of the genotypes did not depicted any relationship between geographical distribution and genetic divergence. The maximum inter-cluster distance was found between clusters X and cluster III followed by that between X and IX and cluster VIII and cluster V. The cluster III gave the best result for ten pod weight and number of pods per plant. Cluster VIII gave best result for number of seeds per pod and number of pods per cluster. For pod length cluster X was best, while plant height was found best in cluster IX. Cluster IV had best values for days to 50% flowering and pod width, cluster II had best result for hundred fresh seeds weight, while, hundred seed weight and ten pod weight contributed maximum towards the total genetic divergence in the material studied.
Based on high yielding genotypes and large inter-cluster distances, it would be advantageous to attempt crossing of the genotypes from cluster X with cluster III and cluster X with cluster IX and cluster VIII with cluster V, which may lead to the generation of broad spectrum of favourable genetic variability for yield improvement in vegetable cowpea.
The data generated by twenty one ISSR markers for 56 genotypes revealed high level of polymorphism. Total 5029 bands were generated with 84.64 % polymorphism. Out of twenty-one, ten primers (UBC-848, UBC-847, UBC-807, UBC-815, UBC-814, UBC-864, UBC-853, UBC-859, UBC-808 and UBC-809) showed 100% polymorphism and the PIC values ranged from 0 to 0.8952.
A dendrogram based on UPGMA analysis of fifty six cowpea genotypes generated by ISSR molecular data gave two main clusters, clusters IA and IB while Jaccard’s similarity coefficient ranged from 0.67 to 0.91. Thus, the results indicated maximum similarity between JCPL-01 and JCPL-75 (91%) and the minimum similarity (70%) was found in JCPL-64 whereas the dendrogram generated by growth habit and quantitative data gave two main clusters, clusters IA and IB and indicated maximum similarity between JCPL-51 and JCPL-35 (77%) and the minimum similarity (46%) was found with JCPL-09 . The dendrograms generated by molecular, growth habit and quantitative data gave two main clusters, clusters IA and IB, the results indicated that the maximum similarity was found between JCPL-65 and JCPL-57 (87%) and minimum similarity (68.25%) was obtained in JCPL-63. In order to develop a good breeding programme, the cultivars from distant cluster can be selected.
The final conclusion that can be revealed from variability, correlation, path analysis, selection indices and genetic divergence study from different traits in cowpea indicated that the number of pods per plant was the most important component character followed by ten pod weight, pod length and hundred fresh seeds weight which should be considered as selection criteria for green pod yield improvement in vegetable cowpea.
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plant breeding