Heterosis and inbreeding depression analysis for yield and its component traits in Black × Amber Wheat Crosses

Introduction

Wheat (Triticum aestivum L.) is a major cereal crop and a staple food for a large proportion of the global population, contributing significantly to food and nutritional security, particularly in countries like India. With increasing demand driven by population growth and changing dietary patterns, improving grain yield and quality remains a key challenge for plant breeders (Shewry and Hey, 2015) [12] . In addition, there is growing interest in developing nutritionally enriched wheat varieties, such as black wheat, which is rich in anthocyanins and exhibits antioxidant properties beneficial to human health (Sharma et al., 2018) [11] . Heterosis, or hybrid vigour, is an important breeding approach for enhancing yield and its component traits. It refers to the superior performance of F₁ hybrids over their parents and is governed by genetic mechanisms such as dominance, overdominance, and epistasis (Shull, 1908) [13] . Although commercial hybrid wheat development is limited, the study of heterosis provides valuable insights into the genetic architecture of complex traits and helps identify superior parental combinations (Longin et al., 2012) [7] . Since grain yield is a complex polygenic trait influenced by traits such as grain number per spike, spike length and tiller number, improvement in these traits can indirectly enhance yield. Previous studies have reported significant heterosis for yield components, suggesting the effectiveness of indirect selection (Fonseca and Patterson, 1968; Singh et al., 2004) [3,14] . Inbreeding depression, defined as the reduction in vigour from the F₁ to F₂ generation due to the breakdown of favourable gene combinations, provides insights into the nature of gene action. High inbreeding depression indicates the importance of non-additive effects, whereas low values suggest additive gene action (Allard, 1999) [1] . Therefore, the combined assessment of heterosis and inbreeding depression is essential for designing effective breeding strategies. The present study was undertaken to estimate heterosis and inbreeding depression for yield and its component traits in six Black × Amber wheat crosses, with the aim of identifying suitable breeding strategies for developing high-yielding and nutritionally enriched wheat varieties.

Materials and Methods

The present investigation was conducted during the rabi seasons of 2020-23 at the Research Farm, Wheat and Barley Section, Department of Genetics and Plant Breeding, CCS Haryana Agricultural University, Hisar, India. The experimental material comprised six crosses derived by crossing black wheat with six amber wheat varieties, namely HD 3059, WH 1124, WH 1270, DBW 303, WH 1184 and HD 3086. Each cross consisted of six generations, viz., P₁, P₂, F₁, F₂, BC₁ and BC₂. The evaluation of all six generations was carried out during rabi 2022-23 under field conditions. The experiment was laid out in a randomized block design with three replications. Controlled hybridization was carried out using standard emasculation and pollination techniques in wheat. Data were recorded for yield and its component traits, including grain yield per plant (g), biological yield per plant (g), harvest index (%), thousand grain weight (g), spike length (cm), number of grains per spike and number of effective tillers per plant. Statistical analysis was carried out using analysis of variance (ANOVA) to test the significance of differences among generations and crosses, following standard procedures described by Snedecor and Cochran (167) [15] and evaluated by Panse and Sukhatme (1954) [8] . Heterosis was estimated as percentage increase or decrease of F₁ over mid-parent and better parent values:

Heterosis over mid parent (Relative heterosis): H1 (Turner, 1953) [16] Where, Heterosis over better parent (Heterobeltiosis): H2 (Fonseca and Patterson, 1968) [3] Where, BP = Mean performance of better parent

Test of significance

The test significance for heterosis and heterobeltiosis were carried out following 't' test as under Standard errors (S.E.) and critical differences were estimated using the following relation Where, Me = Error mean sum of square r = Number of replications The test of significance of relative heterosis and heterobeltiosis were carried out by comparing calculated values of 't' with tabulated values of 't' at 5% and 1% level of significance.

Estimation of inbreeding depression

Inbreeding depression was compared by using the following formulae:

The standard error and 't' value for test of significance for inbreeding depression were calculated as under: Standard error for inbreeding depression 't' test for inbreeding depression The test of significance of inbreeding depression was performed by comparing, calculated 't' value with table 't' value at 5% and 1% level of significance.

Results and Discussion

Heterosis was estimated in terms of mid-parent heterosis (H₁), better-parent heterosis (H₂) and inbreeding depression (ID) across six crosses (Table 1). Heterosis and inbreeding depression were estimated to assess the relative importance of non-additive genetic effects in the inheritance of yield and its component traits. Mid-parent heterosis (MPH) reflects the performance of hybrids relative to the parental mean, whereas better-parent heterosis (BPH) indicates the extent to which hybrids surpass the superior parent. Inbreeding depression (ID), on the other hand, measures the decline in performance from F₁ to F₂ generations due to segregation and breakdown of favourable heterozygous gene combinations (Allard, 1999) [1] . The magnitude and direction of these parameters varied across traits, indicating differences in the underlying genetic control. For grain yield per plant, the highest value of mid-parent heterosis was observed in the cross Black wheat × WH 1124 (2.19%), while the lowest value was recorded in Black wheat × HD 3086 (-0.77%). Heterobeltiosis ranged from -9.34% (Black wheat × WH 1124) to -16.27% (Black wheat × DBW 303). Significant inbreeding depression was observed only in Black wheat × WH 1124 (3.32%). The presence of both positive and negative MPH, while BPH remained consistently negative across all crosses. The presence of positive MPH suggests partial expression of hybrid vigour; however, the absence of positive BPH indicates that hybrids failed to outperform the best parent. The generally low magnitude of inbreeding depression further suggests limited exploitation of heterosis for this trait. Such a pattern is indicative of the predominance of additive effects, where favourable alleles are dispersed among parents and recombination is required to achieve improvement. Similar findings have been reported in wheat by Fonseca and Patterson (1968) [3] , Singh et al. (2004) [14] and Raza et al. (2025) [9] , who observed limited heterobeltiosis for grain yield despite moderate mid-parent heterosis. In case of biological yield per plant, the highest value of midparent heterosis was observed in the cross Black wheat × HD 3086 (2.49%), while the lowest value was recorded in Black wheat × HD 3059 (0.81%). Heterobeltiosis ranged from -7.21% (Black wheat × HD 3059) to -11.56% (Black wheat × WH 1270). Significant negative heterobeltiosis was recorded in all the crosses. Significant negative inbreeding depression was recorded in Black wheat × WH 1270 (-2.63%) and Black wheat × DBW 303 (-2.80%). The predominance of positive MPH suggests improved biomass accumulation in hybrids relative to the parental mean; however, the consistently negative BPH reflects limited superiority over the best parent. The low to moderate magnitude of inbreeding depression, including negative values in some crosses, indicates the involvement of both additive and non-additive gene effects. Comparable results have been reported by Yadav et al. (2025) [17] and Kumar et al. (2024) [6] , highlighting the complex inheritance of biomassrelated traits. [4] and Longin et al. (2012) [7] , emphasizing the complex genetic architecture of harvest index in wheat.

Considering the number of grains per spike, the highest value of mid-parent heterosis was observed in the cross Black wheat × WH 1124 (9.81%), while the lowest value was recorded in Black wheat × HD 3086 (-1.81%). Heterobeltiosis ranged from -7.55% (Black wheat × HD 3086) to 4.10% (Black wheat × WH 1124). Significant positive better-parent heterosis was observed only in Black wheat × WH 1124 (4.10%), whereas significant negative heterobeltiosis was recorded in remaining crosses. Significant positive inbreeding depression was observed in all the crosses, ranging from 5.88% (Black wheat × WH 1124) to 9.97% (Black wheat × DBW 303). The predominance of positive MPH along with occasional positive BPH indicates strong heterotic expression for this trait. However, the moderate to high positive inbreeding depression suggests that the superior performance of F₁ hybrids is not fully retained in subsequent generations due to the breakdown of favourable gene combinations. This pattern reflects the involvement of additive, dominance and epistatic gene effects. These findings are in agreement with earlier reports by Kumar et al. (2024) [6] , Raza et al. (2025) [9] and Burdak et al. (2023) [2] , who also reported significant heterosis and inbreeding depression for this trait.

In thousand grain weight, the highest value of mid-parent heterosis was observed in the cross Black wheat × WH 1270 (6.95%), while the lowest value was recorded in Black wheat × WH 1124 (-0.52%). Heterobeltiosis ranged from -2.48% (Black wheat × HD 3059) to -6.80% (Black wheat × WH 1124).

Inbreeding depression ranged from -1.54% (Black wheat × WH 1270) to -8.36% (Black wheat × WH 1124). The presence of both positive and negative MPH along with predominantly negative BPH suggests limited heterotic advantage for this trait. The low to negative magnitude of inbreeding depression indicates relative stability across generations and reflects the predominance of additive gene action with minimal influence of dominance and epistasis. These findings are consistent with earlier reports by Singh et al. (2004) [14] and Kumar et al. (2017) [4] , indicating that this trait can be effectively improved through selection.

For spike length, the highest value of mid-parent heterosis was observed in the cross Black wheat × WH 1124 ( [17] and Raza et al. (2025) [9] . For effective tillers per plant, the highest value of mid-parent heterosis was observed in the cross Black wheat × HD 3086 (15.86%), while the lowest value was recorded in Black wheat × WH 1124 (9.88%). All the crosses exhibited significant positive mid-parent heterosis. Heterobeltiosis ranged from -1.69% (Black wheat × HD 3059) to -9.77% (Black wheat × WH 1270). Inbreeding depression ranged from 1.84% (Black wheat × HD 3086) to 6.31% (Black wheat × HD 3059). The consistently high positive MPH reflects substantial hybrid vigour for this trait; however, the absence of positive BPH suggests limited superiority over the best parent. The moderate magnitude of inbreeding depression indicates the involvement of non-additive gene effects, particularly dominance and epistasis. These findings are consistent with earlier studies by Kumar et al.

(2024) [6] , Burdak et al. (2023) [2] and Kumar et al. (2017) [4] , which also highlighted the importance of non-additive gene effects for tiller-related traits.

Conclusion

The study revealed variable heterosis and inbreeding depression across traits in six Black × Amber wheat crosses, indicating differences in genetic control. Grain yield per plant showed low heterosis with consistently negative better-parent heterosis and low inbreeding depression, suggesting the predominance of additive gene action and limited scope for direct heterosis exploitation. In contrast, traits such as number of grains per spike, spike length and effective tillers per plant exhibited substantial heterosis along with moderate to high inbreeding depression, indicating the involvement of non-additive gene effects. Thousand grain weight and phenological traits showed low heterosis and inbreeding depression, suggesting their amenability to selection. Overall, recombination breeding with selection in later generations would be effective for developing high-yielding and nutritionally enriched wheat varieties.

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