Combining ability studies in okra [Abelmoschus esculentus (L.) Moench] for growth and earliness parameters through line x tester analysis

Introduction

Okra [Abelmoschus esculentus (L.) Moench] also commonly known as ladies' finger or bhindi is an important vegetable crop originated from tropical Africa. The world biggest producer of okra is India. One of the major issues in okra cultivation in India is lack of specific to location high yielding varieties. In often cross-pollinated crops like okra, improvement in the past was based on selection in locally adapted populations. During recent past, exploitation of hybrid vigour and selection of parents on the basis of combining ability effects have opened a new line of approach in crop improvement. LineTester analysis technique suggested by (Kempthorne 1957) [1] stands as one of the most recognized and systematic methodologies for identifying and selection of superior parents and crosses. This approach serves as a fundamental prerequisite for success in any breeding initiative. Application of biometrical techniques like line x tester analysis has appeared to be the best and vastly useful breeding tool, which gives generalized picture of genetics of the characters under study. Breeding programs focus on selection of better genotypes and hybrids to maximize crop productivity, especially in mineral-rich foods crucial for human diets (Shiri et al., 2024) [2] . The selection of appropriate breeding practices relies on understanding general combining ability (GCA) and specific combining ability (SCA) to capitalize on additive and non-additive gene actions, respectively, as outlined by (Sprague and Tatum, 1942) [3] .

to row spacing of 60cm and 45cm from plant to plant. Five plants were randomly selected for each genotype from each replication and evaluated for the quantitative characters and the replicated mean values of various characters of parents and hybrids were subjected to Line x Tester analysis.

Result and Discussions General Combining Ability

The estimates of gca effects indicated that the parent, AKO-74 (50.78) followed by AKO-Red (16.61), Korchi (6.43) and AKO-10 (3.98) had maximum positive and significant gca effect for growth character plant height. Maximum positive GCA is important for inheritance of plant height character in okra, the result indicated that parents having positive good general combining ability for the same trait. Similar results of significant and positive GCA were also obtained by Keerthana et al. (2024) [4] in okra. The parent AKO-74 (0.64) followed by IC-42472 (0.57) and EC-3293384 had maximum positive and significant gca effect for number of branches per plant. The character number of branches per plant in okra breeding desired in positive direction for inheritance of trait. In okra Kumar et al. (2021) [5] also identified good general combiners for the number of branches per plant. The parent AKO-2 (-0.69) followed by Kokan Bhendi (-0.61) and EC-3293384 (-0.50) recorded the maximum negative and significant gca effect for earliness character internodal length. The results evident that negative combining ability effect for inheritance of inter nodal length. In okra Sayed et al. (2024) [6] also identified good general combiners for the length of inter node. AKO-74 (-2.54) followed by AKO-73 (-1.62), AKO-10 (-1.62) and Korchi (-1.12) recorded the maximum negative and significant gca effect for earliness character days to initiation of first flower. Negative GCA effect is highly desirable for days to initiation of first flower in okra crop and desirable combining ability parental lines are considered for further crossing program. In okra Keerthana et al. (2024) [4] also identified good general combiners for the days to initiation of first flower. The parents AKO-10 (-1.96) followed by Korchi (-1.79), AKO-73 (-1.79) and AKO-74 (-1.79) recorded the maximum negative and significant gca effect for earliness character days to 50% flowering. Negative combining ability effect is highly desirable for the earliness of 50 percent flowering in okra. In okra Pathania et al. (2024) [7] also identified good general combiners for days to 50 percent flowering. The parents AKO-74 (-3.66) followed by AKO-73 (-1.50) and Korchi (-1.22) recorded the maximum negative and significant gca effect for earliness character days to first harvesting on the basis of pooled season. Negative GCA effect is desirable for this character and present study evident the same result. In okra Keerthana et al. (2024) [4] also identified good general combiners for the days to first harvesting.

Specific Combining Ability

The cross Korchi x AKO-10 (36.07) exhibited highest positive significant SCA effects followed by AKO-1-P-2 x Phule Vimukta (33.81), Kokan Bhendi x AKO-11 (30.74) Positively significant SCA effect is good combiner for inheritance of desirable character. Similar results of significant and positive SCA were also obtained by Maurya et al. (2022) [8] and Keerthana et al. (2024) [4] in okra. Kokan Bhendi x AKO-10 (-1.84) recorded the highest negative SCA effects followed by Korchi x AKO-11 (-1.27), AKO-1-P-2 x IC-42472 (-0.90), AKO-1-P-2 x EC-3293384 (-0.89) and Korchi x AKO-Red (-0.88) in pooled. Negatively significant SCA effect is good combiner for inheritance of inter nodal length. In okra Sayed et al. (2024) [6] also identified good general combiners for length of internode. The cross combinations Korchi x IC-42472 (1.69) recorded the highest negative SCA effects followed by AKO-1-P-2 x AKO-2 (1.50) and AKO-1-P-2 x AKO-11 (1.24). The predominance of SCA variance for branches per plant implied that non additive gene action was important in the genetic background for this character. In okra Kumar et al. (2021) [5] also identified good general combiners for the number of branches per plant. The cross AKO-1-P-2 x IC-42472 (-0.88) exhibited highest negative significant SCA effects followed by Kokan Bhendi x AKO-7 (-0.82), AKO-1-P-2 x AKO-74 (-0.77) and Kokan Bhendi x Phule Vimukta (-0.72). In okra Keerthana et al. (2024) [4] also identified high negative significant SCA effects for node at which first flower appear. The cross AKO-1-P-2 x AKO-73 (-2.56) exhibited highest negative significant SCA effects followed by Kokan Bhendi x AKO-2 (-2.47) and Korchi x Arka Anamika (-2.20). In okra Pathania et al. (2024) [7] and Keerthana et al. (2024) [4] also identified high SCA effects for days to initiation of first flower. The cross Korchi x Arka Anamika (-1.78) exhibited highest negative significant SCA effects followed by AKO-1-P-2 x AKO-7 (-1.74) and AKO-1-P-2 x AKO-10 (-1.41). Crosses registered significant and negative SCA effects for days to 50 percent flowering. All the best performer crosses for earliness involve at least one good general combiner. The crosses showing high SCA effects not always involve parents with high GCA effects, suggesting that the interallelic interactions are important for 50 percent flowering. These findings are in conformity with the findings of Pathania et al. (2024) [7] in okra. The cross AKO-1-P-2 x AKO-73 (-3.50) exhibited highest negative significant SCA effects followed by AKO-1-P-2 x AKO-10 (-2.83) and Kokan Bhendi x AKO-1 (-2.39). The result indicated that most of the heterotic hybrids exhibit negatively significant for earliness that is days required for first harvest in present study, which indicates non-additive gene action for the inheritance of the character. Keerthana et al. (2024) [4] also observed SCA for days required for first harvesting in okra.

Conclusion

It was concluded that highly significant variances were observed for both general and specific combining ability for all the characters studied. Considering higher earliness parents Korchi and Kokan Bhendi was found as good general combiner. For earliness purpose the cross combination Kokan Bhendi x AKO-10, Kokan Bhendi x AKO-1 for Internodal length, Korchi x AKO-Red, Korchi x AKO-1 and Kokan Bhendi x Phule Vimukta for Node at which first flower appeared, AKO-1-P-2 x AKO-73, Korchi x AKO-73, AKO-1-P-2 x AKO-74 and Korchi x AKO-74 for days to initiation of first flower, Korchi x EC-3293384, Korchi x AKO-74, AKO-1-P-2 x AKO-10 and Korchi x AKO-73 for days to 50% flowering and AKO-1-P-2 x AKO-74, Korchi AKO-74 for days to first harvest found negatively significant heterosis for the earliness traits. It is suggested that breeding techniques that can accumulate detectable genetic effects while maintaining substantial heterozygosity to take advantage of dominant gene effects have proven to be most beneficial for improving the population studied.

Acknowledgement

AcknowledgementsThe authors express their sincere gratitude to the Department of Vegetable Science, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, for providing the necessary research facilities and support for the successful conduct of the field trials.

References

1. Kempthorne O. An introduction to genetics statistics. New York: John Wiley and Sons; 1957. p. 453-471.
2. Sprague GF, Tatum LA. General vs. specific combining ability in single crosses of corn. J Am Soc Agron. 1942;34:927-932.
3. Kumar A, Gaurav SS, Shiri T. Combining ability studies in okra (Abelmoschus esculentus (L.) Moench) through diallel analysis for yield and yield attributing characters. Pharma Innov J. 2021;10(5):480-485.
4. Syed MR, Tauseef A, Saad J, Faiz UR, Muhammad AS, Zahid H, et al. Combining ability and genetic analysis of morphological and yield related traits in Abelmoschus esculentus L. Sarhad J Agric. 2024;40(1):11-21.
5. Pathania R, Mehta DK, Bhardwaj RK, Dogra RK, Singh K, Kaplex A, et al. Exploitation of heterosis, combining ability and gene action potential for improvement in okra (Abelmoschus esculentus). Indian J Agric Sci. 2024;94(12):1340-1348.