Genetic Diversity, Heritability, Genetic Advance of Growth and Yield Traits of Some Okra (Abelmoschus Esculentus L. Moench) Accessions

Introduction

Okra (Abelmoschus esculentus L. Moench) is one of the most important and widely grown vegetable crops. It is primarily grown for its soft green fruits and leaves, which are generally eaten as fresh vegetables [1]. It is a nourishing vegetable comprising 86.1% water, 2.2% protein, 0.2% fat, 9.7% carbohydrate, 1.0% fibre and 0.8% ash [2]. Okra is also made up of other valuable nutrients. Compared to other fleshy fruit vegetables like Solanum melongena and Lycopersicon esculentum, okra is a better source of calcium and ascorbic acid [3]. It is also a good source of fibre and proteins [4], has extensive culinary [5], therapeutic [6] and industrial [4] properties.

Genetic improvement of okra for yield is significant because of the nutritional and health benefits inherent in it and to overcome the low genetic potential of the existing varieties and environmental factors which are the major constraints to okra yield. Genetic diversity study is done so as to select parents for further breeding work. Breeders often calculate heritability estimate, a value that predicts to what extent their selection effort will be successful. Heritability is defined as the proportion of phenotypic variance that is attributable to an overall genetic variance for the genotype [7]. Adequate knowledge of components of variances and their effects, heritability, and genetic advance of the traits under consideration help to the breeders in deciding the appropriate breeding method to improve the genetic makeup [8]. Johnson HW, et al. [9] reported that the value of heritability estimate is enhanced when used together with the genetic advance. Combined high heritability estimates and high genetic advance shows that variation is attributable to high degree of additive gene effect and selection will be rewardable [10]. Kumar S, et al. [11] reported that before undertaken crop improvement process in any species, a thorough knowledge of the degree of genetic variability existing in the crop for various characters is essential. The nature and magnitude of genotypic and phenotypic variability in any species of crop play an important role in devising successful breeding strategy for developing superior cultivars.

Materials and Methods

Seven accessions of okra collected from the germplasm of National Centre for Genetic Resources and Biotechnology (NACGRAB), Ibadan, Nigeria were grown during rainy season of 2019. The trial was conducted in a randomized complete block design (RCBD) with three replications at the research field of the Department of Plant Science and Biotechnology, Federal University Oye-Ekiti, Ekiti State, Nigeria. The site of experiment is located at 25.570 N latitude, 81.51o E longitude. The average annual rainfall was 1013.4 mm. Each replication consisted of single row for each accession. Each row plot consists of 10 stands per accession planted at 30cm apart. Two seeds were planted into each hole of 2cm deep and later thinned to one after emergence.

Discussion

This may be due to differences in the genetic component of the various accessions. This also corroborates with the findings of Schmidt PJ, et al. [16] and Sharma VR, et al. [17] who stated the role of differences in the genetic components of different varieties in yield determination of okra. The variability can be used to improve the crop for the desired character through selection. This is in accordance with Siemonsma JS, et al. [18] who also recorded variability in different characters of okra genotypes they studied.

The genetic composition of a plant, the environment and the interaction of genotype with environment are pre-requisites for determining the phenotype of a plant. The identification and selection of plants that have genotypes conferring desirable phenotypes, rather than plants with favorable phenotypes due to environmental effects is paramount to successful plant breeding. In crop improvement programme, it is only the genetic component of variation (GCV) that is of significant value because it explains the proportion of the variation that is heritable but phenotypic variation is a function of both genotypic and environmental components. The observed variations in the various quantitative traits among the accessions are due to the effect of genotype and environment.

Phenotypic coefficients of variation were higher in magnitude than genotypic coefficient of variation for all the characters studied which indicates that these traits are influenced by environmental factors. Similar observations were also reported by Yadav M, et al. [19].

Phenotypic coefficient of variation varied from 9.21 for days to germination to 47.92 for number of pods, whereas, genotypic coefficients of variation ranged from 4.97 for number of seeds to 43.54 for plant height at flowering, this indicates considerable diversity in the germplasm studied for various agronomic traits.

Heritability of a character is very important to breeder because it helps him or her to predict the extent to which selection effort will be successful in the next generation. According to Ibrahim MM, et al. [8], heritability is used to establish the extent to which a character may be passed unto the offspring by the parent. Heritability could be regarded as low if it is within the range of 0-30%, 31-60% as average while > 60% is grouped as high [19]. Heritability in the broad sense separates genotypic variance from environmental variance, expresses the extent to which the phenotype is determined by the genotype, which is known as the degree of genetic determination, and very useful in the selection of superior lines from homozygous lines. this signifies that these traits were less influenced by the environmental factor, hence, the presence of additive gene effect is suspected, hence selection for improvement of such characters may be reliable. Similar result was reported by Yadav M, et al. [19] for plant height. The low heritability associated with low genetic advance for number of seeds (26.61, 5.29), number of branches (17.87, 11.48) and number of leaves (12.15, 6.98) revealed that environment or non-additive gene action may be prevailing for these characters and so heterosis breeding will be beneficial.

Conclusion

This study concluded that accessions NGB00378a, NGB00299, NGB00304 and NGB00302 gave higher fruit yields; they flowered earlier, had longer harvesting period and also performed better by producing more fruit yield. NGB00346, NGB00298 and NGB00350 had shorter internode length and their productivity is comparatively low due to low number of fruits per plant. Therefore, these accessions with higher fruit yields have potential for improvement in further okra breeding. Also, a wide range of variability and heritability with high genetic advance was observed for the characters like internode length, days to 50% flowering, number of pods, plant height at maturity and plant height at flowering. Therefore, selection of superior genetic materials based on these performances could be very effective.