The challenges breeders face in producing high yielding varieties in self pollinated crops like wheat are selecting the potential parents and elite cross combinations in early generations that would result in high-yielding isogenic lines following allele fixation (Arya et al., 2017; Thapa et al., 2019; Kumar et al., 2021). Choosing the wrong parents at any point could ruin a carefully thought-out and well-run follow-up programme. Because phenotypically superior lines may result in poor cross combinations for yield, choosing appropriate parents based on phenotypic performance alone is futile, highlighting the significance of assessing the parental genotypes for their combining ability and the resulting hybrid’s potential to exhibit hybrid vigour.
       
Frequently, the high yielding parents may not combine finely to produce a superior hybrid. While the portion of specific combining ability allows the breeder to select higher yielding crosses meant for the exploitation of heterosis and a nonadditive share of genetic variance, knowledge of general combining ability helps the breeder identify superior performing parents who will outperform the rest of the population when used in the hybridization program. The degree of additive and nonadditive gene action is revealed by evaluations of combining ability effects and the extent of variance components. A high SCA indicates a nonadditive form of gene influence, while an additive mode of gene activity is indicated by a high GCA (Sprague and Tatum, 1942). Diallel mating design is one of the most operative biometrical methods for assessing the GCA and SCA effects of different wheat genotypes. It also offers insights into the genetic mechanisms governing grain yield and other traits. Considering the above, our current study aimed to examine the general and specific combining ability effects and variances and the type and extent of gene-action related to yield and yield-attributing traits.

Ten parental distinct bread wheat genotypes [CAL/NH//H567.71/3/SER1/4/CAL/NH/H567.71/5/2*KAU2/6/… (P1), HD 3234 (P2), PBW 692(P3), HUW 640 (P4), DBW 189 (P5), VORB/SOKOLL (P6), UP 2762 (P7), UP 2901 (P8), QLD 73 (P9) and QLD 65 (P10)] were crossed in a half diallel manner to produce their 45 F₁ hybrids. In Rabi 2018-19, a total of 55 entries were assessed using three replications in Randomized Block Design at N. E. Borlaug CRC, G.B. Pant University of Agriculture and Technology, Pantnagar, India. The parental genotypes and resulting hybrids were planted in two-row plots, each measuring 1 m in length, having an inter and intra-row distance of 20 cm and 10 cm, respectively. Standard agricultural procedures and cultural operations were closely adhered to to encourage the best possible growth and expression of the material. The following twelve specific traits were observed in five competitive plants chosen randomly from each of the three replications: days to 75% heading, flag leaf area (cm²), days to maturity, plant height (cm), productive tillers per plant, spike length (cm), spikelets per spike, grains per spike, biological and grain yield per plant (g), harvest index (%) and 1000-grain weight (g) and each plot’s days to maturity and days to 75% heading were noted. Following the conventional protocols set by Panse and Sukhatme (1985), the average mean of the recorded observations was subjected to analysis of variance. Therefore, to assess the interactions of general and specific combining ability effects, a combining ability study was also conducted using Griffing’s Method II (Griffing, 1956), which comprised the parents and one set of F₁ hybrids excluding reciprocals, in conjunction with Model I (fixed effect).

The ANOVA demonstrated highly significant mean squares due to GCA for traits such as days to 75% heading, productive tillers, plant height, days to maturity, grains per spike, 1000-grain weight, biological yield, grain yield and harvest index (Table 1). Conversely, spike length showed significant mean squares and two traits (flag leaf area and spikelets per spike) displayed non-significant mean squares. The mean squares resulting from SCA were highly significant for traits like days to 75% heading, flag leaf area, productive tillers per plant, plant height, grains per spike, 1000-grain weight, biological yield, grain yield per plant and harvest index. In contrast, it was significant for days to maturity and non-significant for spike length and spikelets per spike. The manifestation of these traits involved both additive and nonadditive effects, as demonstrated by the significance of both general and specific combining abilities.


 
Variance components of combining ability
 
The variance estimates for general (σ²gca) and specific (σ²sca) combining ability are provided in Table 1. The estimated value of σ²g was higher than its σ²s for days to 75% heading, indicating that additive gene action predominated. However, nonadditive gene activity was more prevalent in the remaining attributes. The prevalence of nonadditive variance contributed comparatively more to the expression of various traits in wheat, as testified by Ali et al. (2020) and Askander et al. (2021).
 
GCA and SCA effects
 
The parents having significant GCA effects in the desired direction were classified as good general combiners (+), those having non-significant GCA effects were average general combiners (0) and those with significant GCA effects in the undesired direction were poor general combiners (-) (Table 2). These estimates are shown in Table 3 and 4 for both general and specific combining ability effects.






       
In drought-prone conditions, breeding wheat for early maturity is a sensible drought-avoidance tactic that enables plants to avoid terminal drought stress. For days to 75% heading and days to maturity, three parental genotypes (UP 2762, UP 2901 and CAL/NH//H567.71/3/SER1/4/CAL/NH/H567.71/5/2*KAU2/6/…) displayed significant negative GCA effects. The crosses that had the potential to improve earliness in wheat were VORB/SOKOLL×QLD 73 and CAL/NH//H567.71/3/SER1/4/CAL/NH/H567.71/5/2*KAU2/6/...×QLD 65 for days to 75% heading and VORB/SOKOLL×QLD 65 and HD 3234×DBW 189 for days to maturity. These crosses had strong negative SCA effects. Usually, dwarf plants are more desirable because they are more lodging resistant; however, depending upon the requirement, tall plants can also be preferred as they can be utilized for straw purposes. Only two parents had significant negative GCA effects for plant height. HD 3234 was the top general combiner for reduced plant height, VORB/SOKOLL had the lowest general combining ability and seven crosses had significant negative SCA effects. No parent showed significant GCA effects for the flag leaf area; however, nine crosses showed significant positive SCA effects. VORB/SOKOLL had a significant positive GCA value for productive tillers per plant and eleven crosses displayed significant positive SCA effects. Only one parent, PBW 692, showed significant positive GCA effects on spike length and two crosses (VORB/SOKOLL×UP 2762 and HD 3234×UP 2762) exhibited notable positive SCA effects. These outcomes are consistent with those of Joshi et al. (2020), Dahiya et al. (2023) and Bhatt et al. (2024).
       
Selection for significant yield contributory traits, such as spikelets per spike, grains per spike and 1000-grain weight, is desirable. For spikelets per spike, none of the parents displayed statistically significant positive GCA effects; nevertheless, HUW 640, QLD 65, HD 3234, UP 2762 and PBW 692 were the parents with positive GCA effects. Out of 45 crosses, only three (HUW 640×DBW 189, HUW 640×VORB/SOKOLL and HD 3234×UP 2762) exhibited substantial positive SCA effects. Five crosses (VORB/SOKOLL×QLD 73, PBW 692×HUW 640, UP 2762×QLD 73, HUW 640×QLD 65 and CAL/NH//H567.71/3/SER1/4/CAL/NH/H567.71/5/2*KAU2/6/…×UP 2901) demonstrated significantly positive SCA effects, while the parents, DBW 189, QLD73 and UP 2901, demonstrated significant positive GCA effects for grains per spike. CAL/NH//H567.71/ 3/SER1/4/CAL/NH//H567.71/5/2*KAU2/6/…, QLD 73 and DBW 189 were the parents exhibiting significant favourable GCA impacts for 1000-grain weight. SCA effects for 1000-grain weight were significantly positive in eleven crosses. Significantly positive GCA effects were noted for two parents, CAL/NH//H567.71/3/SER1/4/CAL/NH/H567.71/5/2*KAU2/6/… and DBW 189, in terms of biological yield. Sixteen crosses unveiled significant SCA effects with six crosses (VORB/SOKOLL×QLD 65, CAL/NH//H567.71/3/SER1/4/ CAL/NH/ H567.71/5/2*KAU2/6/…×PBW 692, HD 3234×UP 2901, HD 3234×PBW 692, DBW 189×QLD 73 and HUW 640×DBW 189) showing significantly positive effects and ten crosses presenting significantly negative effects.
       
Three parents-CAL/NH//H567.71/3/SER1/4/CAL/NH/H567.71/5/2*KAU2/6/…, DBW 189 and UP 2901-presented significantly positive GCA effects for grain yield, while VORB/SOKOLL, UP 2762, PBW 692, QLD 73 and QLD 65 presented significantly negative GCA effects. Of these, eleven crosses displayed significantly positive SCA effects for grain yield. For harvest index, only one parent (VORB/SOKOLL) demonstrated significantly positive GCA effects and nine crosses displayed significant SCA effects. Similar types of results for these characters have been testified by Mahdy et al. (2022), Rind et al. (2023), Ahmad and Gupta (2024), Bhatt et al. (2024) and Singh and Shrivastav (2025).
       
Hence, to increase the overall GCA for yield in bread wheat, it is advised that the breeder ought to focus on the superior combining ability for each component trait. Selecting parent plants displaying strong GCA for multiple traits is essential for creating a dynamic population rich in favourable genes. Restricted recurrent selection by intermating the most desirable segregants following subsequent selection or multiple crossing/biparental mating in early segregating generations will improve traits exhibiting dominance or nonadditive gene effects. Another useful breeding technique for using nonadditive gene effects is heterosis breeding. The parental genotypes CAL/NH//H567.71/3/SER1/4/CAL/NH/H567.71/5/2*KAU2/6/…, DBW 189 and UP 2901 confirmed sound GCA effects for grain yield along with its attributing components and can be valuable in the hybridization programmes (Table 5). Incorporating the parents with good GCA and F₁ hybrids with high SCA into multiple crosses may also be a beneficial strategy for the noticeable increase in wheat grain yield.

The study found substantial variation across parental lines and crosses for most characters, except spike length, where GCA and SCA were negligible. This showed that improvements can be made for all traits, except spike length, by selecting superior genotypes or isolating transgressive segregants. UP 2762 was the best general combiner for days to maturity, making it appropriate for creating lines with early maturity. CAL/NH//H567.71/3/SER1/4/CAL/NH/H567.71/5/2*KAU2/6/… can be utilized as one of the parents in hybridization programs to increase 1000-grain weight and grain yield. The crosses, viz., CAL/NH//H567.71/3/SER1/4/CAL/NH/H567.71/5/2*KAU2/6/…×PBW 692 and HD 3234×UP 2762 were determined to be good crosses due to them having significant SCA effects for yield and two yield attributing traits, respectively. As such, they offered a chance for commercial exploitation either as hybrid varieties or as a base material for choosing potential homozygous lines from transgressive segregants to increase bread wheat yield levels.

The present study was supported by Department of Genetics and Plant Breeding, Govind Ballabh Pant University of Agriculture and Technology, Pantnagar.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.
 
Informed consent
 
All animal procedures for experiments were approved by the Committee of Experimental Animal care and handling techniques were approved by the University of Animal Care Committee.

The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsor-ship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.