Combining ability studies for fruit yield and its component traits through diallel analysis in okra [Abelmoschus esculentus (L.) Moench]

Introduction

Okra (Abelmoschus esculentus (L.) Moench), a member of the family Malvaceae, is an economically important vegetable crop cultivated widely in tropical and subtropical regions. In India, it occupies approximately 0.531 million hectares with an annual production of 6.46 million tonnes and an average productivity of 12.17 t ha⁻¹ (Anonymous, 2022) [1] . The crop is valued for its nutritional quality, adaptability, short duration, and high market demand. However, productivity is often limited by a narrow genetic base and susceptibility to various biotic and abiotic stresses, necessitating the development of superior high-yielding cultivars. Combining ability analysis is an important tool in plant breeding for identifying superior parents and cross combinations and understanding the nature of gene action governing quantitative traits. Estimation of General Combining Ability (GCA) and Specific Combining Ability (SCA) provides valuable information for selecting suitable parents and exploiting heterosis in hybrid breeding programmes. Therefore, the present investigation was undertaken to evaluate the combining ability of ten diverse okra genotypes using a halfdiallel mating design and to identify promising parents and hybrids for fruit yield and its component traits.

These 45 F 1 along with their 10 parents and one standard check (GJOH 4) were evaluated in a randomized complete block design with three replicates during kharif (July to October) 2023.Inter and intra row spacing was kept 60 and 30 cm, respectively. Agronomic practices followed as per the standard recommendation and sufficient protection measures were taken to raise a healthy crop. So in this experiment analysis based on fruit yield and its other traits present in okra. Observations were recorded on days to 50% flowering, fruits per plant, fruit length (cm), fruit girth (cm), fruit weight (g), fruit yield per plant (g), plant height (cm) and internodal length (cm). Days to 50% flowering, plant height and internodal length was consider as negative trait in okra so low scoring parent consider as a better parent for estimation of heterobeltiosis. The combining ability analysis was done by following Model 1 (fixed effect) and Method 2 (Parents and hybrids without reciprocals) of Griffing (1956 a ) and Griffing (1956 b ) [3,4]

Results and discussion

Combining ability and gene action

The analysis of variance for combining ability for eight gca sca for fruit yield per plant and other trait under study was found less than unity. Therefore, prime role of preponderance non-additive gene action was observed for inheritance of all the traits.

General and specific combining ability effects 1. Days to 50% flowering

Parents with negative gca effect and hybrids with negative sca effect were considered as best for this trait because earliness was desirable trait in okra. The gca effects of parents ranged from -2.21 to 1.91. Among parents, the GAO 5 (-2.21) followed by GAO 8 (-0.82) and JOL 20-04 (-0.51) exhibited significant negative gca effects which confirmed to be good general combiner for this trait (Table 2). The sca effects for days to 50% flowering ranged from -6.02 to 9.70. Among them the crosses viz., JOL 20-04 × GAO 8 (-6.02) had highest significant negative sca effects followed by JOL 18-12 × Pusa Sawani (-5.96) and JOL 18-07 × GP2 (-5.43) for this trait so this crosses were good specific combiner (Table 3). The result of days to 50% flowering for gca and sca effect were in accordance with Budha Ram (2015) [2] , Satish et al. (2017) [13] , Makdoomi et al. (2018) [7] , Sapavadiya et al. (2019) [12] , Vekariya et al. (2020) [17] , Patel et al. (2021) [10] and Shinde et al. (2023) [14] .

Fruits per plant

Positive value of gca and sca effect was considered as desirable for fruits per plant. The gca effects of parents ranged from -1.39 to 1.55. JOL 20-04 (1.55) showed highest significant positive gca effects followed by GAO 5 (1.24), GP1 (0.84) and GAO 8 (0.71) which indicating good general combiner for fruits per plant (Table 2). The range of sca effects for fruits per plant varied from -5.02 to 5.23. The cross JOL 18-07 × GAO 5 (5.23) considered good specific combiner followed by JOL 20-04 × JOL 18-12 (5.13) and GAO 5 × GO 6 (4.72) (Table 3). The results of gca and sca effects fruit per plant were comparable with findings of Budha Ram (2015) [2] , Kumar and Reddy (2016) [6] , Satish et al. (2017) [13] , Makdoomi et al. (2018) [7] , Vekariya et al. (2020) [17] , Patel et al. (2021) [10] and Shinde et al. (2023) [14] .

Fruit length

For fruit length character, significant positive value of gca effect for parents and sca effect for crosses had to be considered as desirable. The gca effect for fruit length ranged from -0.46 to 0.67. Among parents, GP2 (0.67) exhibited maximum significant positive gca effect, which was desirable for the character (Table 2). The cross JOL 20-04 × GAO 8 (1.78) was found superior specific combiner for fruit length followed by GO 6 × Pusa Sawani (1.65) and JOL 20-04 × GAO 5 (1.38) (Table 3). The results of gca and sca effects for fruit length were in confirmation with findings of Nagesh et al. (2014) [9] , Budha Ram (2015) [2] , Kumar and Reddy (2016) [6] , Jupiter and Kandasamy (2017) [5] , Paul et al. (2017) [11] , Vekariya et al. (2020) [17] , Patel et al. (2021) [10] and Shinde et al. (2023) [14] .

Fruit girth

The gca effects of parents ranged from -0.23 to 0.25 for fruit girth. Four parent exhibited significant positive gca effects GP2 (0.25), JOL 18-07 (0.10), GAO 8 (0.09) and JOL 18-12 (0.07) that suggests to be this parents were good general combiner for improving fruit girth (Table 2). The sca effect of hybrids ranged from -0.72 to 0.95. 9 cross recorded significant positive sca effect for fruit girth. The cross GP2 × Pusa Sawani (0.95) followed by GP1 × GAO 8 (0.73), JOL 20-04 × GAO 8 (0.72) and JOL 18-07 × GP2 (0.72) possessed significant positive sca effect. Thus, this cross considered as good specific combiner for this trait (Table 3). Fruit girth gca and sca effect conformity with Vekariya et al. (2020) [17] , Patel et al. (2021) [10] and Shinde et al. (2023) [14] .

Fruit weight

The gca effects of parents ranged from -0.71 to 1.31 for this trait. In addition, the parent, GAO 8 (1.31) depicted significant positive gca effects that concludes to be good general combiner for the character (Table 2). The sca effects ranged from -2.44 to 2.83 for fruit weight. Top four good specific combiners were GP2 × GAO 8 (2.83), GAO 5 × GO 6 (2.56), JOL 20-04 × JOL 18-12 (2.32) and JOL 18-12 × GP1 (2.32) for this trait (Table 4). The gca and sca effects of fruit weight were in accordance with Kumar and Reddy (2016) [6] , Jupiter and Kandasamy (2017) [5] , Paul et al. (2017) [11] , Makdoomi et al. (2018) [7] , Patel et al. (2021) [10] and Shinde et al. (2023) [14] .

Fruit yield per plant

The gca effects of parents ranged from -31.24 to 32.74 for fruit yield per plant. Four parents, GAO 8 (32.74), GO 6 (10.63), JOL 20-04 (9.07) and GP1 (6.50) exhibited significant and positive gca effects that suggests to be good general combiner for fruit yield per plant (Table 2). The hybrids, JOL 18-07 × GAO 5 (90.74) observed highest significant positive sca effects followed by GAO 5 × GO 6 (88.51) and JOL 20-04 × JOL 18-12 (84.27) that indicated to be good specific combiner for this trait (Table 4). Budha Ram (2015) [2] , Kumar and Reddy (2016) [6] , Jupiter and Kandasamy (2017) [5] , Paul et al. (2017) [11] , Makdoomi et al. (2018) [7] , Vekariya et al. (2020) [17] , Patel et al. (2021) [10] and Shinde et al. (2023) [14] recorded similar results and confirmation with gca and sca effects for fruit yield per plant.

Plant height

Ranged of gca effect was from -7.21 to 11.96 for plant height. Plant height was negative trait in okra so, the lower value was considered as desirable for this trait. Out of ten parents under study, three parents reported significant and negative gca effect for plant height. Based on the significant negative gca effect JOL 18-07 (-7.21) followed by NOL 11-12 (-6.27) and GP 1 (-5.16) were found good general combiners for plant height (Table 2). For plant height, sca effect ranged from -27.77 to 30.67. Seven crosses registered significant and negative sca effect. Top three crosses NOL 11-12 ×GO 6(-27.77), GO 6 × GAO 8 (-25.51) and GAO 5 × Pusa Sawani (-23.52) had significant and negative sca effect for plant height. Hence, these crosses were considered as good specific combiner for this trait (Table 4). The present investigation of gca and sca effects for plant height were in agreement with the Singh et al. (2006) [16] , Mehta et al. (2007) [8] , Weerasekara et al. (2008) [19] , Wammanda et al. (2010) [18] , Singh (2011) [15] .

Internodal length

Internodal length was negative trait in okra so, the lower value was desirable for this trait. Out of the 10 parents under study, three parents NOL 11-12 (-0.65), JOL 18-07 (-0.60) and GP1 (-0.41) registered significant and negative gca effect (Table 2). The cross NOL 11-12 × GO 6 (-2.51) possessed maximum sca effect followed by the crosses GO 6 × GAO 8 (-2.40) and GAO 5 × Pusa Sawani (-2.12) (Table 4). Kumar and Reddy (2016) [6] , Paul et al. (2017) [11] , Satish et al. (2017) [13] , Makdoomi et al. (2018) [7] , Vekariya et al. (2020) [17] , Patel et al. (2021) [10] and Shinde et al. (2023) [14] recorded similar results and confirmation with gca and sca effects for internodal length. Parents were classified as good, average and poor combiners based on result of gca effects for different traits are presented in Table 5. Among all the parental genotypes under study, JOL 20-04 was found promising for other traits like days to 50% flowering and fruit yield per plant. Parental line NOL 11-12 was found good general combiner for plant height and internodal length. JOL-18-07 was found good general combiner for fruit girth, plant height and internodal length. Parent JOL 18-12 was found good general combiner of fruit girth. GP 2 was reported good general combiner for fruit length and fruit girth. GP 1 was reported good general combiner of fruits per plant, fruit yield per plant, plant height and internodal length. Parent GAO 5 was found good general combiner of days to 50% flowering, fruits per plant, fruit length and fruit yield per plant. These parents have resulted in the production of superior single cross hybrids. GAO 8 was found good general combiner of all the trait except plant height. Hence these parental genotypes could be utilized in future breeding programmes for exploitation of hybrid vigour and also to generate a greater number of desirable segregants for fruit yield and yield attributing characters. The crosses exhibiting high mean performance may results from either good × good, good × average, average × average and poor × poor general combining parents. The good general combining parents when crossed do not always produce high sca effects. While, poor general combining parents not always produce low sca effects. So, any parental combination may result into high sca effects. Best performing top five hybrids having high specific combining ability effects for fruit yield per plant and other characters found with desirable direction presented in Table 6. The crosses JOL 18-07 × GAO 5 (90.74), GAO 5 × GO 6 (88.51), JOL 20-04 × JOL 18-12 (84.27), GP 2 × GP 1 (75.81) and JOL 18-12 × GO 6 (71.39) were reported with high and significant positive specific combining ability effects for fruit yield per plant. The hybrid JOL 18-07 × GAO 5 with high mean performance 313.80 g exhibited highest significant positive sca effect 90.74 for fruit yield per plant with the desirable and significant sca effects for days to 50% flowering, fruits per plant, fruit weight and internodal length. Next superior hybrid, GAO 5 × GO 6 had mean performance 338.08 g and significant positive sca effect 88.51 for fruit yield per plant. This cross also exhibited positive and desirable sca effect for days to 50% flowering and fruits per plant. The third crosses JOL 20-04 × JOL 18-12 had mean performance 321.54 g and significant positive sca effect 84.27 for fruit yield per plant. This cross also exhibited positive and desirable sca effect for days to 50% flowering, fruits per plant, fruit girth and fruit weight.

Conclusion

The present study identified significant variation in combining ability among the parental genotypes and hybrids for fruit yield and its component traits in okra. The parents GAO 8, GO 6, JOL 20-04, and GP1 were recognized as superior general combiners, indicating their potential as valuable donors in future breeding programmes. Among the hybrids, JOL 18-07 × GAO 5, GAO 5 × GO 6, JOL 20-04 × JOL 18-12, GP2 × GP1, and JOL 18-12 × GO 6 exhibited high and significant specific combining ability effects for fruit yield per plant along with several important yieldcontributing traits, making them promising candidates for hybrid development.

The σ²GCA/σ²SCA ratio was less than unity for fruit yield and all other traits studied, indicating the predominance of non-additive gene action in their inheritance. These findings suggest that heterosis breeding would be an effective approach for improving fruit yield and related traits in okra. Furthermore, the exploitation of non-additive genetic effects through biparental mating followed by selection in early segregating generations may facilitate the accumulation of favourable alleles and the identification of desirable transgressive segregants. Overall, the superior parents and cross combinations identified in this study provide valuable genetic resources for developing high-yielding and improved okra cultivars.

References

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