GENETIC ANALYSIS OF AGRO-NUTRITIONAL TRAITS IN CROSSES AND INBRED LINES OF OKRA (Abelmoschus esculentus L. Moench) UNDER CONTRASTING ENVIRONMENTS

Abstract

ABSTRACT Okra (Abelmoschus esculentus) has notable nutraceutical and therapeutic attributes. However, it is underexploited and the genetic diversity of this crop is enormous for precise evaluation of its nutritional enhancement. This investigation was done to assess genetic diversity, environmental stability, combining ability, gene action, and nutritional value of various okra genotypes. Four experiments were carried out at the Teaching and Research Farms of the Federal University of Agriculture, Abeokuta (7.15°N, 3.36°E), and Olabisi Onabanjo University, Ayetoro (7° 14′20.62′′N, 3° 1′57.31′′E) from May 2018 to December 2021, using randomized complete block design in three replications. Thirteen agronomic and morphological descriptors were used to evaluate genetic variability among 30 Okra inbred lines. Thereafter, hybridization was done using the Line-by-tester mating design (three lines and nine testers). The twelve parents and 27 crosses obtained were evaluated morphologically in wet and dry seasons of 2019 and 2021. Nutritional evaluation was used to determine mineral contents (calcium, iron, and Vitamins A, C, and E). Data were subjected to analysis of variance while means were separated using Duncan’s Multiple Range Test at 5% probability level. Correlation, Coefficients of Variability (PCV, GCV), broad–sense heritability (Hb), and Genetic Advance (GA) were estimated. Additive and Dominance components, Gene Action, Combining Abilities (General and Specific), GGE Biplot and Single Linkage Clustering Analysis (SLCA) were also done to determine variability, gene effects and stability patterns. Results revealed significant (p ≤ 0.01) differences among the inbred lines and their crosses for all traits except leaf length and breadth and peduncle length. Locations, seasons, genotypes, and interactions also showed significant differences (p ≤ 0.01, p≤ 0.05) for fruit yield (FY) and 1000 seed weight (1000SW). The results also revealed highly significant values among the parents and their crosses for calcium, iron, zinc and vitamins. Significant and positive correlation was recorded for number of fruits per plant, FY and 1000SW across all environments. High PCV was recorded for calcium (25%) and iron (22%). PCV ranged from 39% (number of plants) to 14% (peduncle length). High heritability was observed for 1000SW (100%), while fruit diameter had low heritability (3.27%). Genetic advance was also high for plant height (32.74) but low for leaf breadth (3.41) and leaf length (9.18). The best general combiners for fruit yield were P1, P3, P5, P6, P7, while the best specific combiners for fruit yield were P1XP4, P1XP8, P2XP8, P3XP4, P3XP12. Results of the GGE biplot showed that the 8 environments fell into one sector where Abeokuta 2019 (wet season) is the most representative environment. Both G21 (NGB00322 x Yeleen) and G22 (NGB00326 x NGB00297) possess high yield and stable attributes. Eight clusters were identified in this study with Cluster I having the highest calcium and iron contents and cluster VI having the highest Vitamin A content. The study concluded that plant height, number of fruits, fruit length, fruit diameter and individual fruit weight are best characters to be selected for yield improvement, while P1XP8, P1XP11, P2XP7, P2XP11, P3XP9, P1XP8 and P1XP11 are superior hybrids for yield improvement