Genetic studies on heterosis estimation and combining ability analysis in bhendi (Abelmoschus esculentus)

Introduction

A vital vegetable crop grown throughout India and other tropical regions, Bhendi (Abelmoschus esculentus) is essential to both food security and farmer incomes. Enhancing the sustainability and productivity of bhendi production has emerged as a major area of attention for agricultural development initiatives due to the fast increase in the demand for vegetables worldwide Singh, A. & Pandey, M. K. 2024 [11] . In response, the creation of highyielding, disease-resistant hybrids that can adapt to a variety of agroclimatic situations is becoming a top priority for plant breeders. The two main genetic concepts that drive hybrid breeding are heterosis and combining ability. The ability of parental lines to create hybrids with desired characteristics including increased yield, disease and insect resistance, and improved nutritional quality is known as "combining ability." Begna, T. (2021) [1] . The phenomena whereby hybrid offspring outperform their parents in traits like growth rate, yield potential, and stress tolerance is known as heterosis, or hybrid vigour. Ability and heterosis are two basic genetic concepts that drive hybrid breeding. Combining ability is the ability of parental lines to create hybrids with desired characteristics including increased nutritional value, resistance to pests and diseases, and greater yield. T. Begna. 2021 [1] . The phenomenon known as heterosis, or hybrid vigour, occurs when hybrid offspring outperform their parents in characteristics such as growth rate, yield potential, and stress tolerance. Although hybrid breeding has advanced significantly, there are still a number of obstacles to overcome. The limited availability of genetically diverse parental lines is a significant drawback that may limit the possibility of attaining high combining ability and heterotic response (Singh, R. & Singh, S. 2023) [12] . Furthermore, a more thorough investigation of the genetic and molecular mechanisms underlying complex features like improved drought tolerance or resistance to particular diseases is required in order to produce hybrids with these qualities. This article aims to present a thorough analysis of the state of the art concerning the combination of heterosis and ability in hybrid bhendi. Key discoveries, difficulties, and future directions for this field of study will be discussed. Through the investigation of intricate relationships between parent lines and hybrids, we may fully utilise hybrid breeding and produce superior bhendi types that are advantageous to both farmers and consumers.

Materials and Methods

During the 2024 bhendi growing seasons, the experimental study was carried out at the Campus Farm, Kalasalingam School of Agriculture and Horticulture, KARE. In 2024, a diallel mating pattern was created by crossing seven bhendi lines: Arka Anamika, Madurai Local, Virudhunagar Local, Parbhani Kranti, Tenkasi Local, Lakshmi 1, and Villupuram Local. During the trial, every suggested agronomic technique and plant protection measure under irrigated conditions was adhered to. Plants were spaced 30 cm apart and rows were spaced 60 cm apart. Data on yield and yield component features, including plant height, number of branches per plant, fruit length, fruit weight, number of fruits per plant, number of seeds per fruit, and internode distance, were recorded for randomly chosen plants per entry every replication. In 2024, 42 hybrids' F1 seeds, seven parents, and a typical check hybrid Varsha Uphar were raised. In order to maintain 10 plants in each row, 30 crossings were cultivated in two replications using a randomised block design (RBD). Each cross was placed in two rows, each measuring 6 m in length, with a 90 cm gap between rows and a 60 cm gap between plants. To evaluate their combining capacity, the parents were also raised in the nearby block with four rows for each entry, spaced 90 x 45 cm apart, along with a typical check hybrid. Five plants were chosen at random from each genotype in each replication to assess important biometrical characteristics. Plant height, internode length, fruit length, number of seeds per fruit, number of branches per plant, number of fruits per plant, average fruit weight, and fruit yield per plant were among the traits evaluated. The TNAUSTAT software program was used to statistically analyse the mean data from parents, hybrids, and standard checks for heterosis and combining ability. Replication and treatment caused each of the seven traits' total variation to be divided into components. In order to facilitate comprehension and debate, yield-related characteristic data were methodically tabulated, and the analysis of variance (ANOVA) results were provided together with estimates of standard error and critical difference (CD). Additionally, standard heterosis values were computed by comparing them to check hybrids. The TNAUSTAT software was used for all statistical calculations.

Results and Discussions

Significant genetic variety between the parent plants and their 42 hybrid combinations was revealed by the analysis of variance (Table 1). With a significantly better fruit output per plant than the parental average, P1 outperformed P5, P6, and P4 among the seven parents under study, making them excellent choices for crossbreeding initiatives. (Table 2). In terms of fruit yield, 18 of the 42 hybrids-both direct and reciprocal-outperformed the hybrid mean. The hybrids P2 × P5, P2 × P6, P4 × P2, P5 × P4, P4 × P5, P6 × P3, and P7 × P3 were notable for their remarkable yields, which reached about 550g per plant (Table 5). These hybrids show great promise since they are the result of crossings in which at least one parent line has advantageous features or both parent lines performed well in terms of yield. This finding is in line with recent research that highlights the importance of parental selection in maximising hybrid performance and yield-related traits, such as that conducted by Waikhom Jupiter Singh et al. (2022) [16] and Janarthanan & Sundaram (2020) [3] . The efficacy of high-yield hybrids in breeding selection was further supported by the fact that they continuously displayed important beneficial features, such as more fruits per plant, more branching, and higher average fruit weight. With the exception of internodal distance, days to fruit maturity, fruit girth, and number of branches per plant, the analysis of combining ability variances showed substantial differences in general combining ability (GCA) and specialised combining ability (SCA) for the majority of variables (Table 4). This implies that both additive and nonadditive genetic variance are present in the inheritance of traits. For the majority of traits, the GCA/SCA ratio was noteworthy because it was greater than unity. This suggests that additive genetic variance has a significant impact on important traits like the number of days until the first flowering, plant height, internodal distance, number of immature seeds per fruit, number of branches per plant, fruit girth, and number of fruits per plant. On the other hand, days to fruit maturity, fruit length, average fruit weight, and total fruit production were all significantly influenced by non-additive genetic variance. Similar results have been observed in recent research, such as those by Vinithra et al. (2019) [15] , Sundaram et al. (2020) [3] , and Shwetha et al. (2022) [9] , supporting the genetic basis of these features. While non-additive genetic variance might be better utilised in subsequent generations, the presence of additive genetic variance implies that improvement techniques like pure line selection or pedigree selection could successfully enhance desired traits. For better bhendi breeding results, a combination strategy that includes population improvement initiatives could maximise both variance types. Similar results have been observed in recent research, such as those by Vinithra et al. (2019) [15] , Sundaram et al. (2020) [3] , and Shwetha et al. (2022) [9] , supporting the genetic basis of these features. While non-additive genetic variance might be better utilised in subsequent generations, the presence of additive genetic variance implies that improvement techniques like pure line selection or pedigree selection could successfully enhance desired traits. For better bhendi breeding results, a combination strategy that includes population improvement initiatives could maximise both variance types. Reciprocal recurrent selection in a population improvement program would be the most successful hybrid development technique due to the existence of reciprocal differences across several attributes. This strategy maximises hybrid performance and guarantees long-term genetic gains by enabling the simultaneous exploitation of additive and nonadditive genetic variance.

Relationship between per se performance and combining ability effects

P1, P5, P6, and P4 were the parental lines that showed the strongest GCA effects across a variety of attributes among those studied. In particular, P1 showed favourable GCA impacts for average fruit weight, fruit length, number of branches per plant, and days to first flowering. Days to initial flowering, plant height, internode distance, number of immature seeds per fruit, and fruit girth were all positively impacted by GCA in P5. Days to fruit maturity, the number of immature seeds per fruit, and the number of branches per plant were all positively impacted by P6. With positive GCA effects for internode distance, days to fruit maturity, number of branches per plant, fruit length, average fruit weight, and fruit yield per plant, P4 stood up as a superior combiner (Table 2). Interestingly, P4 was the only parent with both high yield and positive GCA effects, whereas P1, P5, and P6 recorded high fruit yield per plant but showed negative GCA effects for fruit yield. P4 was the top combiner when evaluating total GCA performance, followed by P5 and P7. P5 and P4 are excellent prospects for varietal breeding programs due to their outstanding per se performance and high GCA effects, which indicate significant additive genetic variability. Nine hybrids (P1 × P3, P2 × P5, P2 × P6, P4 × P2, P4 × P5, P5 × P4, P6 × P3, P6 × P7, and P7 × P3) showed substantial positive SCA impacts on fruit yield per plant out of the 18 hybrids that outperformed the hybrid mean in fruit yield. Notably, hybrids with the highest mean fruit output per plant, including P2 × P5, P2 × P6, P4 × P2, P5 × P4, P4 × P5, P6 × P3, and P7 × P3, also showed positive SCA effects across a number of characteristics, including fruit yield per plant. Current research on heterosis in bhendi hybrids has reaffirmed how important specific combining ability (SCA) is for increasing production. Along with beneficial SCA effects for important traits as average fruit weight, fruit length, number of fruits per plant, and number of branches per plant, the hybrids P2 × P5, P4 × P5, and P4 × P5 showed the highest mean fruit output per plant. P6 × P3 demonstrated favourable SCA effects for fruit yield per plant and number of fruits per plant, but P4 × P2, P2 × P6, and P7 × P3 displayed strong SCA effects for fruit yield per plant and average fruit weight (Table 4). The hybrids P2 × P5, P6 × P7, P1 × P3, P1 × P4, P3 × P7, P4 × P5, P5 × P7, P2 × P4, and P2 × P7 were shown to be good specific combiners when evaluating overall SCA performance across eleven variables. Furthermore, P2 × P5, P4 × P2, P2 × P6, P7 × P3, and P5 × P4 showed favourable heterobeltiosis for fruit output per plant, with the exception of fruit length, fruit girth, and the number of branches per plant. These results are consistent with recent studies by Waikhom Jupiter Singh et al. (2022) [16] , which highlight the significance of hybrid selection based on SCA effects and heterosis. Recent studies have emphasised the significance of standard heterosis among the three types of heterosis in maximising hybrid vigour. In terms of fruit output per plant, the hybrids P2 × P5 (79.16%), P2 × P6 (45.15%), P4 × P2 (45.04%), P5 × P4 (35.71%), and P4 × P5 (34.88%) showed the highest standard heterosis, exceeding 35%. With the exception of plant height, fruit length, and fruit girth, these hybrids likewise showed good standard heterosis across the majority of characteristics. Furthermore, hybrids with high standard heterosis for fruit production per plant also have standard heterosis of about 25% for number of fruits per plant, another important productive feature. These results are consistent with recent studies that highlight the function of hybrid selection based on heterosis effects, such as those conducted by Siva Ranjani et al. (2020) [13] , Johnny Subakar Ivin & Anbuselvam (2021) [6] , and Ebenezer Babu Rajan et al. (2022) [2] . Recent research have emphasised the significance of conventional heterosis in optimising hybrid vigour, hence reaffirming its applicability in bhendi breeding initiatives.

References

1. Begna T. Combining ability and heterosis in plant improvement. Open J Plant Sci. 2021;6(1):143-150.
2. Rajan EB, Ramesh B, Ramesh K, Sathya P, Priya V, et al. Heterosis and hybrid performance in bhendi for yield and yield components. Pharma Innov J. 2022;11(12):632-637.
3. Janarthanan R, Sundaram N. Studies on the mean performance of F₂ segregants of bhendi. Int J Curr Microbiol Appl Sci. 2020;9(8):2652-2660.
4. Javia RM. Heterosis and combining ability studies in okra (Abelmoschus esculentus L. Moench) through line × tester analysis. Asian J Biol Sci. 2013;6(2):145-151.
5. Gopi JS, Hampannavar M. Concept of heterotic groups and reciprocal recurrent selection in hybrid breeding. J Pharmacogn Phytochem. 2018;7(5):2504-2507.
6. Ivin JS, Anbuselvam M. Studies on line × tester analysis and magnitude of heterosis in bhendi. Ann Agri-Bio Res. 2021;26(2):160-162.
7. Mudhalvan M, Senthilkumar N. Combining ability, reciprocal effects and heterosis for fruit yield characters in okra (Abelmoschus esculentus [L.] Moench). J Pharmacogn Phytochem. 2021;10(1):96-101.
8. Pachiyappan R, Saravanan K. Combining ability for yield and yield components characters of bhendi (Abelmoschus esculentus L. Moench). Electron J Plant Breed. 2019;9(1):321-331.
9. Shwetha R, Deepa R, Anusha K, Sridevi P, Suma R, et al. Genetic variability studies in okra (Abelmoschus esculentus [L.] Moench) for yield and yield contributing traits. Pharma Innov J. 2022;11(6):287290.
10. Singh AK, Singh MC, Pandey S. Line × tester analysis for combining ability in okra (Abelmoschus esculentus [L.] Moench). Agric Sci Digest. 2012;32(2):91-97.
11. Singh AK, Pandey MK. Advances in okra (Abelmoschus esculentus L.) breeding: integrating genomics for enhanced crop improvement. J Adv Biol Biotechnol. 2024;27(5):397-407.
12. Singh R, Singh S. Combining ability and heterosis in okra (Abelmoschus esculentus L.): implications for hybrid development. Indian J Agric Sci. 2023;93(1):1220.
13. Ranjani S, Devi M, Kumar A, Prabha S, Valli R, et al. Estimation of standard heterosis in bhendi (Abelmoschus esculentus [L.] Moench). Plant Arch. 2020;20(1):2070-2072.
14. Sundaram N, Kumar S, Priya D, Ramesh R, Anitha M, et al. Genetic analysis in F₄ generation of bhendi for growth and yield. Int J Curr Microbiol Appl Sci. 2020;9(10):339-345.
15. Vinithra M, Babu S, Aravind J, Kumar R, et al. Studies on genetic parameters, correlation and causation among biometrical traits in bhendi. Electron J Plant Breed. 2019;10(4):1541-1546.
16. Singh WJ, Devi R, Devi S, Singh L, et al. Potential heterosis in bhendi (Abelmoschus esculentus [L.] Moench). Pharma Innov J. 2022;11(12):632-637