Genetic evaluation and heterosis studies through diallel crossing for yield and quality in yardlong bean [Vigna unguiculata subsp. sesquipedalis (L.) Verdcourt.]

Introduction

Yardlong bean [Vigna unguiculata subsp. sesquipedalis (L.) Verdc.], also known as asparagus bean or snake bean, is an important warm-season legume vegetable cultivated widely across tropical and subtropical Asia for its long, tender, succulent pods. Besides being a rich and inexpensive source of dietary protein, dietary fibre and vitamins, the crop contributes significantly to household nutritional security and offers remunerative returns to smallholder vegetable growers. Consumer preference for yardlong bean is closely linked to pod quality attributes such as protein content, crude fibre, ascorbic acid concentration and post-harvest shelf life, in addition to pod yield, making simultaneous improvement of yield and quality a key breeding objective. Heterosis breeding through diallel mating offers an effective route for combining favourable alleles governing yield and quality from diverse parents into superior hybrid combinations, while diallel analysis further permits identification of parents with high combining ability for use in recombination breeding. Although several studies have reported variability for yield and biometric traits in yardlong bean, information on the heterotic performance of quality parameters such as protein, crude fibre, vitamin C and keeping quality in a systematic diallel set remains limited. The present investigation was therefore undertaken to evaluate six diverse parents and their thirty F₁ hybrids for pod yield and key quality traits, and to identify superior hybrid combinations with potential for commercial exploitation and future recombination breeding in yardlong bean.

Materials and Methods

The present investigation was carried out at the College Farm, Department of Horticulture, Pandit Jawaharlal Nehru College of Agriculture and Research Institute (PAJANCOA & RI), Karaikal, Union Territory of Puducherry, India, situated between 10°49' S-11°01' N latitude and 78°43' W-79°52' E longitude, at an altitude of 4 m above mean sea level. The experimental soil was sandy loam with medium fertility, and the site experiences a tropical climate with a hot summer. The crop was raised under irrigation drawn from a rain-water harvesting pond within the farm. Six genetically diverse and superior yardlong bean genotypes-Arka Mangala (P₁), Vyjayanthi (P₂), Vellayani Jyothika (P₃), Lola (P₄), VS 28 (P₅) and VS 54 (P₆)-were selected from evaluation studies done with 69 yardlong bean genotypes as parents on the basis of prior variability and genetic divergencestudies were intercrossed in a diallel mating design to generate thirty F₁ hybrid combinations. The resulting thirty hybrids, the six parents and a standard commercial check hybrid, Iris Super Long-77 (BigHaat, Bengaluru, Karnataka), were evaluated together in a Randomized Block Design with two replications during Jan-April 2026.

Quality traits: Pod yield plant⁻¹ (g) was recorded from total marketable pod weight harvested per plant. Crude fibre content (%, dry-weight basis) of pods at harvestable maturity was estimated following the acid-alkali digestion procedure of Chopra and Kanwar (1976) [4] , wherein the sample was successively digested in dilute sulphuric acid and sodium hydroxide, and the loss in weight on ignition of the dried residue was expressed as percent crude fibre. Protein content (%, fresh-weight basis) of tender pods was determined by the Lowry method as described by Sadasivam and Manickam (1996) [8] , based on colour development with alkaline copper sulphate and Folin-Ciocalteu reagent and measurement of absorbance at 660 nm against a bovine serum albumin standard curve. Ascorbic acid content (mg 100 g⁻¹) was estimated by the 2,6-dichlorophenol-indophenol visual titration method of Sadasivam and Manickam (1996) [8] , based on the reduction of the blue dye to a colourless leuco-base by ascorbic acid in the sample extract. Keeping quality (days) was recorded as the number of days for which harvested pods, held under ambient room conditions, retained their colour, glossiness and freshness for consumption. The data recorded for all traits were subjected to analysis of variance appropriate to the Randomized Block Design, and treatment means were compared using the critical difference at 5 percent and 1 percent levels of significance.

Results and Discussion

Substantial and significant variability was observed among the six parents and thirty F₁ hybrids for pod yield and all the quality traits studied, indicating ample scope for the identification of superior hybrid combinations for commercial exploitation as well as for use as donor parents in recombination breeding.

Mean pod yield plant⁻¹ among the parents ranged from 664.79 g (P₄) to 756.84 g (P₁), with P₁ exceeding the parental mean of 710.72 g. Among the hybrids, values ranged from 901.60 g (P₄ × P₃) to 1149.58 g (P₁ × P₃), the latter substantially exceeding the hybrid mean of 979.67 g. Nineteen of the thirty hybrids outperformed the hybrid mean for pod yield, with P₁ × P₃ consistently recording the highest yield across the evaluation. Comparable superiority of the best-performing hybrid for pod yield in yardlong bean has been reported by Ratnakumari et al. (2023) [7] , and a similar magnitude of yield variation among hybrids has been documented by Sherly et al. (2025) [9] and Abhimanyu et al. (2025) [1] in yardlong bean.

Protein content among the parents varied from 6.48% (P₅) to 13.58% (P₃), with P₃ exceeding the parental mean of 11.06%. Among the hybrids, values ranged from 14.60% (P₅ × P₄) to 16.90% (P₁ × P₃), the latter exceeding the hybrid mean of 15.46%. The majority of hybrids recorded higher protein content than the hybrid mean, reflecting a marked heterotic improvement in nutritional quality over the parental values. Similarly wide protein variability among yardlong bean accessions has been reported by Choi et al. (2024) [2] , while Quamruzzaman et al. (2022) [6] emphasized protein content as an important quality-evaluation criterion in yardlong bean.

Crude fibre among the parents ranged from 4.82% (P₁) to 5.89% (P₄), with P₄ exceeding the parental mean of 5.43%. Among the hybrids, values ranged from 4.90% (P₁ × P₃) to 5.98% (P₂ × P₅); notably, P₁ × P₃ recorded the lowest crude fibre, below the hybrid mean of 5.43%, reflecting a heterotic reduction in fibre content and consequently improved pod tenderness and quality. A comparable heterotic reduction in fibre content has been reported by Quamruzzaman et al. (2022) [6] and Sherly et al. (2025) [9] in yardlong bean, and by Choi et al. (2024) [2] among yardlong bean genotypes.

Vitamin C content among the parents ranged from 12.15 mg 100 g⁻¹ (P₄) to 18.86 mg 100 g⁻¹ (P₁), with P₁ exceeding the parental mean of 16.69 mg 100 g⁻¹. Among the hybrids, values ranged from 20.19 mg 100 g⁻¹ (P₄ × P₅) to 22.80 mg 100 g⁻¹ (P₁ × P₆), the latter exceeding the hybrid mean of 21.06 mg 100 g⁻¹. Most hybrids recorded higher vitamin C content than the hybrid mean, indicating good potential for improving the antioxidant quality of pods through hybridization. Comparably wide vitamin C variability among yardlong bean accessions has been reported by Choi et al. (2024) [2] , and a similar range has been highlighted as a quality-improvement target by Quamruzzaman et al. (2022) [6] .

Keeping quality among the parents ranged from 2.79 days (P₂) to 5.61 days (P₁), with P₁ exceeding the parental mean of 4.32 days. Among the hybrids, values ranged from 6.10 days (P₆ × P₁) to 7.20 days (P₁ × P₆), the latter exceeding the hybrid mean of 6.64 days. Most hybrids exceeded the hybrid mean for keeping quality, indicating a marked heterotic improvement in post-harvest shelf life. A comparable range in shelf-life-related quality traits in yardlong bean has been reported by Sherly et al. (2025) [9] , Quamruzzaman et al. (2022) [6] , while analogous variability in post-harvest vigour traits has been documented in common bean by Mang'ache et al. (2026) [5] .

Taken together, the hybrid P₁ × P₃ combined the highest pod yield and protein content with the lowest crude fibre, while P₁ × P₆ exhibited the best combination of vitamin C content and keeping quality, and P₅ × P₃ also performed consistently well across yield and quality traits. These three crosses, arising predominantly from the parent P₁ (Arka Mangala), which itself was among the superior parents for most quality traits, appear to be the most promising combinations for simultaneous improvement of yield and pod quality and merit further evaluation for possible commercial release or use as base material in recombination breeding programmes in yardlong bean.

Conclusion

The present study revealed considerable heterotic potential for pod yield and quality improvement in yardlong bean through diallel hybridization among six diverse parents. The hybrids P₁ × P₃, P₁ × P₆ and P₅ × P₃ emerged as the most promising combinations, recording superior pod yield along with enhanced protein and vitamin C content, reduced crude fibre and improved keeping quality relative to their parents and the standard check. These findings underscore the value of Arka Mangala (P₁) as a superior general combiner for quality traits and support the use of these elite hybrid combinations, either for direct commercial exploitation after further multi-location testing or as source material for recombination breeding aimed at combining high yield with superior nutritional and post-harvest quality in yardlong bean.

Acknowledgement

The authors gratefully acknowledge the Department of Horticulture, Pandit Jawaharlal Nehru College of Agriculture and Research Institute, Karaikal, for providing the experimental facilities.

References

1. Abhimanyu R, Shinde US, Dhumal SA, Sarvade SA, Pawar RD, Mote MS. Correlation and path analysis in yard long bean genotypes for yield and its attributing character. Plant Archives. 2025;25(2):1273-1280.
2. Choi YM, Shin MJ, Yoon H, Lee S, Yi J, Wang X, et al. Nutritional qualities, metabolite contents, and antioxidant capacities of yardlong beans (Vigna unguiculata subsp. sesquipedalis) of different pod and seed colors. Antioxidants. 2024;13(9):1134.
3. Chopade UD, Yoon H, Shin MJ, Lee S, Yi J, Jeon YA, et al. Multivariate analysis of biochemical properties reveals diversity among yardlong beans of different origins. Antioxidants. 2024;13(4):463.
4. Chopra SL, Kanwar JS. Analytical agricultural chemistry. Ludhiana: Kalyani Publishers; 1976.
5. Mang'ache MC, Binagwa PH, Tryphone GM. Effects of salinity on biofortified common bean (Phaseolus vulgaris L.) varieties for seed germination and seed vigour. Current Journal of Applied Science and Technology. 2026;45(1):103-132.
6. Quamruzzaman A, Islam F, Akter L, Khatun A, Mallick SR, Gaber A, et al. Evaluation of the quality of yardlong bean (Vigna unguiculata subsp. sesquipedalis L.) cultivars to meet the nutritional security of increasing population. Agronomy. 2022;12(9):2195.
7. Ratnakumari N, Naidu LN, Reddy RVSK, Kiran Patro TSKK, Ratna Babu D, Umakrishna K. Studies on heterosis for pod yield and protein content in yardlong bean (Vigna unguiculata (L.) Walp. ssp. sesquipedalis Verdc.). International Journal of Plant & Soil Science. 2023;35(19):1152-1159.
8. Sadasivam S, Manickam A. Biochemical methods. 2nd ed. New Delhi: New Age International; 1996.
9. Sherly J, Sumithra S, Kanthaswamy V, Manojkumar K. Screening of yardlong bean (Vigna unguiculata subsp. sesquipedalis) genotypes under coastal region of Karaikal, India. Plant Archives. 2025;25(1):211-217.