Assessment of Genetic Diversity in Okra [Abelmoschus esculentus (L.) Moench]

Introduction Okra (Abelmoschus esculentus (L.) Moench) is a soft woody dicotyledonous herb, which belongs to the family Malvaceae. It is widely cultivated in the tropics and sub-tropics for its tender and nutritious fruits (Chinatu and Okocha, 2006). Okra is a powerhouse of valuable nutrients, low in calories, fat-free and provides a valuable supplementary nutrition in human diet in developing countries (Kumar and Sreeparvathy, 2010). Okra is an often cross-pollinated crop hence heterosis can be exploited to develop new hybrids. To develop high yielding varieties of okra, genetic diversity through Mahalanobis’ D 2 statistic International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 8 Number 07 (2019) Journal homepage: http://www.ijcmas. com The present investigation was carried out at Horticulture Research Station, Dr. Y. S. R Horticultural University, Venkataramannagudem, West Godavari district during kharif season, 2018.Based on D 2 values, the twenty-nine hybrids of okra grouped into six clusters. Among the sixclusters, cluster III comprised the maximum number of hybrids (6) followed by cluster II (5), cluster V (5), cluster VI (5), cluster I (4) and cluster IV (4). The maximum inter cluster distance was observed between clusters I and VI (D 2 =65.06) followed by clusters II and VI (D 2 =62.51). Highest percent contribution towards divergence came from average fruit weight (17.49 %) followed by fruit yield per plant (13.30 %), fruit and shoot borer infestation on plants (12.07%), plant height (11.33%) and number of seeds per fruit (10.34%). The data on inter cluster distances suggested that selection of one or two elite genotypes from divergent (I & VI) and (II & VI) clusters based on the above characters and crossing them would result in more heterotic and novel hybrids in okra. K e y w o r d s Okra, Genetic diversity, Mahalanobis D statistics, Cluster Accepted: 15 June 2019 Available Online: 10 July 2019 Article Info Int.J.Curr.Microbiol. App.Sci (2019) 8(7): 1923-1931 1924 (Mahalanobis, 1936) used as an important tool to select genetically diverse parents with high yield and wider adaptability in breeding programme. Progress of any breeding programmes depends largely on the availability of genetic variability for desirable traits in genotypes (Balai et al., 2014). Genetic diversity helps the breeders in deciding the most appropriate breeding method to increase the genetic potentialities as well as to surpass the yield barrier (Langade et al., 2013). Therefore, genetic diversity is prerequisite for any successful breeding programme. So, the present experiment formulated to study the genetic divergenc eand clustering pattern of the okra hybrids. Materials and Methods The experimental material comprised of 29 hybrids of okra. Thesehybrids evaluated by raising each entry in a plot of 2.5 m length and 2.5 m width, at a spacing of 60 × 45 cm in a randomized block design with three replications at Horticulture Research Station, Venkataramannagudem during kharif, 2018. The observations were recorded on five randomly selected plants per plot in each replication for seventeen biometric characters viz., plant height (cm), number of primary branches per plant, days to fifty per cent flowering, node at which first flower appear, internodal length of main stem (cm), number of nodes per plant, fruit length (cm), fruit girth (cm), average fruit weight (g), number of fruits per plant, number of seeds per fruit, fruit yield per plant (g), leaf chlorophyll content(SPAD Units), fruit moisture content (%),mucilage content(g/kg), fruit and shoot borer infestation (FSB) on fruits (%) and yellow vein mosaic virus infestation (YVMV) on plants (%). The data collected on different characters was analysed using Mahalanobis (1928) D 2 analysis to determine the genetic divergence among the hybrids and to classify the hybrids in to different clusters using Ward’s method. The character contribution towards genetic divergence was computed using the method given by Singh and Chaudhary (1977). Results and Discussion In this experiment, agglomerative hierarchical clustering technique based on seventeen quantitative characters allocated the twentynine hybrids of okra into six clusters (Table 1 and Fig. 1). The magnitude of D 2 values confirmed that there was significant amount of diversity in the experimental material evaluated by the high inter-cluster and low intra cluster D 2 values.Cluster III comprised the maximum number of hybrids (6) followed by cluster II (5), cluster V (5), cluster VI (5), cluster I (4) and cluster IV (4). The inter and intra cluster D 2 values presented in Table 2 and Figure 2 showed that the inter cluster average D 2 value was maximum between cluster I and cluster VI (D 2 =65.06) followed by cluster II and VI (D 2 =62.51) indicating that the hybrids belonging to these clusters were genetically most divergent. However inter cluster D 2 value was least between cluster IV and VI (D 2 =36.77) clearly indicating the close relation between the hybrids present in these clusters. Among the six clusters, cluster III showed maximum intra-cluster distance (D 2 =29.45) followed by cluster IV (D 2 =27.12) and cluster I (D 2 =26.57) whereas lowest intra cluster distance was recorded in cluster VI (D 2 =20.59) which may be due to limited gene exchange or selection practices among the hybrids for diverse characters. These results are in accordance with the findings of Singh et al., (2018). The cluster mean of twenty-nine hybrids presented in the Table 3 revealed that the mean value of clusters varied in magnitude for all the seventeen characters under this study. Int.J.Curr.Microbiol. App.Sci (2019) 8(7): 1923-1931 1925 Table.1 Clustering pattern of okra hybrids Cluster No. of genotypes Genotypes I 4 (Acc-3 × Acc-01), (Acc-3 × Acc-40), (Acc-17 × Acc-43), (Acc-40 × Acc-43) II 5 (Acc-3 × Acc-41), (Acc-16 × Acc-40), (Acc-17 × Acc-01), (Acc-17 × Acc-40), (Acc-41 × Acc-01) III 6 (Acc-3 × Acc-29), (Acc-16 × Acc-17), (Acc-16 × Acc-29), (Acc-16 × Acc-43),(Acc-1 × Acc-29), Mona 002 IV 4 (Acc-16 × Acc-01), (Acc-40 × Acc-29), (Acc-41 × Acc-43), (Acc-43 × Acc-29) V 5 (Acc-3 × Acc-16), (Acc-3 × Acc-17), (Acc-17 × Acc-41), (Acc-40 × Acc-41), (Acc-41 × Acc-29) VI 5 (Acc-3 × Acc-43), (Acc-16 × Acc-41), (Acc-17 × Acc-29), (Acc-40 × Acc-01), (Acc-43 × Acc-01) Table.2 D 2 Inter and intra cluster distances of okra hybrids: Ward Cluster 1 Cluster 2 Cluster 3 Cluster 4 Cluster 5 Cluster 6 Cluster 1 Cluster 26.57 38.99 39.53 50.70 44.89 65.06 2 Cluster 26.06 39.39 41.29 44.62 62.51 3 Cluster 29.45 38.73 37.99 48.23 4 Cluster 27.12 48.44 36.77 5 Cluster 25.37 38.87