Heterosis and combining ability for growth and yield traits in Tomato (Solanum lycopersicum L.) under protected condition

Introduction

Tomato (Solanum lycopersicum L.) is one of the most important vegetable crops belonging to the family Solanaceae with a diploid chromosome number of 2n = 2x = 24 and is believed to have originated in Peru, South America (Rick, 1969). Owing to its high nutritional and economic value, tomato has become an important crop for both fresh consumption and processing. Heterosis or hybrid vigour, refers to the superior performance of F₁ hybrids over their parents for growth, yield and other economically important traits. The success of heterosis breeding largely depends on the identification of genetically superior parents through combining ability analysis, which provides information on the nature of gene action governing quantitative traits. General Combining Ability (GCA) reflects additive gene effects, whereas Specific Combining Ability (SCA) is associated with non-additive gene effects. Since growth and yield are complex quantitative traits influenced by both genetic and environmental factors, the combined assessment of heterosis and combining ability is essential for identifying superior parents and promising hybrid combinations. Therefore, the present investigation was undertaken to estimate heterosis and combining ability for growth and yield parameters in tomato under protected cultivation.

Material and Methods

The present investigation was conducted at the College of Horticulture, Mudigere, to develop tomato hybrids with improved growth and yield traits under protected cultivation. Six diverse parental lines were crossed using a half-diallel mating design to produce 15 F₁ hybrids, which, along with the parents and a commercial check, were evaluated in a Randomized Complete Block Design (RCBD). Standard crop management practices, including nursery raising, hybridization, transplanting, fertilization, irrigation, training and pruning, were followed throughout the experiment. Observations were recorded on important growth and parameters. The collected data were statistically analyzed using Analysis of Variance (ANOVA) and heterosis was estimated over the mid-parent, better parent and commercial check. General Combining Ability (GCA) and Specific Combining Ability (SCA) analyses were performed following Griffing's Model-I to determine the nature of gene action governing the studied traits. Where, r = number of replications g = number of genotypes p = number of parents h = number of hybrids

Statistical analysis 2.1.1 Analysis of variance

Heterosis

Mid -parent heterosis (%) = (F 1 -MP) MP × 100

Better parent heterosis (%) = (F₁ -BP) BP × 100

Standard heterosis (%) = (F₁ -SC) SC × 100 Where, S g = Sum of squares due to general combining ability S g = 1 / p+2{Σ (Xi + Xii) 2 -4 X 2 } Ss = Sum of squares due to specific combining ability Ss = Σ ΣX 2 ij -1 / P + 2 Σ (Xi + Xii) 2 + 2/ (P + 1) (P + 2) X 2 . I ≤ j P = Number of parents X i = Array total involving i th recurrent parent X ii = Mean value of ith parent X ij = General total of 'P' parental line and P (P-1) / 2 progenies X ij = Mean value of ij th cross M e = Error mean square (M e / r)

ANOVA for combining ability

Source of Variation

Degrees of freedom

Sum of squares

Mean sum of squares

General and Specific Combining Ability effects

The general and specific combining ability effects were estimated as under,

Where, P = Number of parents gi = General combining ability effect of i th parent si j = Specific combining ability effect of the crossinvolving i th and j th parents Yi = Total of array involving i th parent Yj = Total of array involving the j th parent Yii = Parental value of the i th parent Yj j = Parental value of the n th parent Y. = Total of all 𝑃(𝑃+1) 2 items of the diallel table

Results and Discussion

ANOVA for growth and yield parameters

The ANOVA revealed highly significant differences among genotypes for all the growth and yield traits, indicating the presence of substantial genetic variability. Significant variation among parents and hybrids suggests good potential for selecting superior genotypes. The significant parent vs. hybrid comparisons for most traits indicate the presence of heterosis, while the low error mean squares confirm the reliability and precision of the experimental results. Overall, the findings demonstrate the effectiveness of the breeding material for developing high-yielding tomato hybrids (Table 1). [3] . Significant variation was observed for number of branches per plant. Pusa Ruby (9.67) and Pusa Ruby × CHMT-4 (9.10) recorded the highest values among parents and hybrids, respectively (Table 2). Mid-parent, better-parent and standard heterosis ranged from (-36.84 to 45.74%), (-56.55 to 30.43%) and (-57.42 to 9.63%), respectively (Table 3). Enhanced branching may be attributed to favourable genetic interactions and efficient assimilate partitioning. These findings agree with Singh et al. (2024) [21,22] . For days to first flowering, CHMT- [5,8] . Leaf area differed significantly among genotypes. CHMT (2026) [12,16] .

Yield parameters

The number of fruits per plant varied significantly among the genotypes. [11,20,21,22] . Average fruit weight differed significantly among the genotypes. CHMT-4 (64.32 g) and Pusa Ruby × CHMT-4 (74.82 g) recorded the highest values among the parents and hybrids, respectively (Table 2). Mid-parent heterosis ranged from (-5.00 to 28.27%), better-parent heterosis from (-12.00 to 24.44%) and the highest standard heterosis (11.46%) was observed in Pusa Ruby × CHMT-4, suggesting efficient assimilate partitioning and favourable non-additive gene effects (Table 4). These findings agree with Nevani et al.

(2022), and Lalramhlimi et al. (2025) [11,15] . The number of locules per fruit showed significant variation among the genotypes. Pusa Ruby (4. [3,21,22] .

Combining ability studies

The ANOVA for combining ability revealed highly significant (p ≤ 0.01) differences for both GCA and SCA for all the characters studied, indicating the involvement of both additive and non-additive gene effects. Higher GCA variance than SCA variance was observed for number of branches per plant, number of fruits per plant, fruit yield per plot, average fruit weight and number of locules per fruit, suggesting the predominance of additive gene action (Table 5). In contrast, plant height, days to first flowering and leaf area exhibited relatively higher SCA variance, indicating the importance of non-additive gene action. The low error variances confirmed the reliability of the experimental results. Overall, additive gene effects predominated for most yield-related traits, indicating the effectiveness of selection, while non-additive gene action can be exploited through heterosis breeding for specific traits.

General and Specific Combining Ability 3.3.1 Growth parameters

For plant height at 90 DAS, positive and highly significant GCA effects were observed in CHMT-4 (0.84) and CHMT-1 (0.53), whereas Arka Vikas (-1.01) and CHMT-20 (-0.44) exhibited highly significant negative effects (Table 6). The hybrid CHMT-1 × CHMT-20 (4.65) showed the maximum highly significant positive SCA effect, followed by Arka Vikas × CHMT-4 (4.02). On the other hand, the lowest negative SCA effects was recorded in the cross combination, Pusa Ruby × Arka Vikas (-3.25) followed by CHMT-4 × CHMT-1 (-3.09) (Table 7). Similarly, both positive and negative GCA and SCA effects were observed in parents and hybrids, respectively in the research conducted by Mishra et al. (2020) and Kathimba et al.

For number of branches per plant at 90 DAS, Pusa Ruby (1.30) and CHMT-4 (1.28) showed highly significant and highest positive GCA effects, while Arka Vikas (-1.42) and CHMT-20 (-0.50) recorded highest highly significant negative effects. Among the hybrids, Arka Vikas × CHMT-20 (1.79) expressed the highest positive and highly significant SCA effect, followed by Pusa Ruby × Krishna Prabha Shalmala (1.54). Significant negative SCA effects were observed in Pusa Ruby × Arka Vikas (-1.81) and Pusa Ruby × CHMT-1 (- [9,14,24] . Among the parental lines, Krishna Prabha Shalmala (0.25) recorded a highly significant and highest positive GCA effect, indicating the earliness, whereas CHMT-4 (-0.22) showed a significant negative effect. Out of 15 direct crosses, two crosses showed highest and highly significant positive SCA effect in the desired direction which included the cross CHMT-4 × CHMT-20 (1.16) followed by Krishna Prabha Shalmala × CHMT-20 (0.81). Maximum highly significant negative SCA effects were observed in CHMT-4 × CHMT-1 (-1.20) followed by Pusa Ruby × Krishna Prabha Shalmala (-0.95). Farwah et al. (2022) and Kumar et al. (2023b) [10] also revealed that parents and hybrids in tomato exhibited positive and negative GCA and SCA effects.

The estimates of GCA effects revealed that CHMT-4 (0.80), CHMT-1 (0.59) and Krishna Prabha Shalmala (0.13) were good general combiners for leaf area as they exhibited highly significant positive effects. whereas, Arka Vikas (- (2022) [4,14] .

Yield parameters

The parents, CHMT-4 (1.65) and Pusa Ruby (1.41) were identified as the best general combiners, while Arka Vikas (-1.80) showed the highest negative GCA effect. [6] and Javed et al. (2022) [4,13] .The parents, CHMT- [5,17,18] . The parents, CHMT-4 (5.12) and Pusa Ruby (2.37) were identified as superior general combiners, while Arka Vikas (-4.90) exhibited the highest negative GCA effect. Arka Vikas × CHMT-20 (8.85) and Pusa Ruby × Krishna Prabha Shalmala (7.54) recorded the highest positive SCA effects, indicating favourable dominance and epistatic interactions governing fruit development (Table 7). (2022) [1,4] . Among the parents, CHMT-20 (0.15) and Arka Vikas (0.12) were the best general combiners, whereas CHMT- [18,23] .

Plate 1: Best performing hybrids

Conclusion

The present investigation revealed significant genetic variability among the parental lines and F₁ hybrids for all the growth and yield parameters, indicating good scope for tomato improvement through hybrid breeding. Superior heterotic performance was observed in crosses such as Pusa Ruby × CHMT-4 for yield-related traits and CHMT-1 × CHMT-20 for plant height, highlighting their potential for commercial exploitation. Combining ability analysis indicated that both additive and non-additive gene actions governed the studied traits, with additive effects predominating for most yield attributes, while non-additive effects were important for specific growth traits. Overall, the identified superior parents and hybrids can be effectively utilized in future tomato breeding programmes aimed at developing high-yielding and productive hybrids.

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