Wheat, Heterosis, Heterobeltiosis, Standard heterosis Line × Tester, Grain Yield, Dominance.

Wheat (Triticum aestivum L.) is one of the most important cereal crops, providing food for more than one-third of the world's population which belongs to genus Triticum and family Poaceae. It is a staple food source for a large population of the world and also provides a range of diversified baked food products. It offers 20% of dietary calories and protein globally, significantly contributing to food security (Sharma et al., 2022). It is assumed that the yield of the semi-dwarf wheat varieties hits a plateau which can be due to the restricted exploitation of the gene pool and genetic constituent of characters that leads to high yield. According to research studies, the use of heterosis can break the wheat yield plateau. Heterosis is the genetic expression of favorable effects of hybridization to increase or decrease in vigour of hybrids when compared with that of its parents (Joshi and Kumar 2020). The use of heterosis in a self-pollinated crop like wheat is significantly determined by its magnitude and direction. The study on heterosis directly affects the breeding strategy to be used for varietal improvement. Investigation on heterosis also sheds light on the combining ability of the parents and their utilization in breeding programmes. 

Experimental material was developed through 24 crosses between 3 testers viz., Raj 4079, Raj 4238 and DBW 110 and 8 lines viz., Raj 3077, Raj 3765, Raj 3777, Raj 4037, Raj 4120, Sonalika, Kalyan Sona and GW 322 in Line × Tester design during Rabi, 2021-22. Subsequently, the resulting 24 F1s crosses along with parents (lines and testers) and standard check (HI 1544) were evaluated at ARS, Ummedganj, Kota, Rajasthan under three different environmental conditions viz., Early sowing (30/10/2022) (E1), Normal sowing (17/11/2022) (E2) and Late sowing (05/12/2022) (E3) during Rabi, 2022-23. Recommended cultural practices were adopted in order to raise a healthy crop. The observations were recorded for 12 characters viz., dаyѕ to 50% flowerіng, dаyѕ to 75% mаturіty, plant height (cm), number of effective tillers per plant, number of grаіnѕ per head, test weight (g), bіologісаl yіeld per plаnt (g), grаіn yіeld per plаnt (g), hаrveѕt index (%), proteіn сontent (%), zinc content (ppm) and iron content (ppm) іn grаіns (The iron and zinc estimation were done by using Atomic Absorption Spectrophotometer by following the method proposed by Jackson (1973). Heterosis was estimated for 24 hybrids for 12 characters using the formulae given by Fonseca and Patterson (1968) and Standard heterosis according to Meredith and Bridge (1972).

Pooled analysis of variance (Table 1) for testers were highly significant for all the traits except number of effective tillers per plant, number of grаіnѕ per head, bіologісаl yіeld per plаnt, grаіn yіeld per plаnt and hаrveѕt index. Pooled analysis of mean squares due to lines vs. testers showed significant variation for most of the characters except bіologісаl yіeld per plаnt and protein content. The pooled analysis of variance due to parents vs. hybrids indicated significant response for all characters except dаyѕ to 50% flowerіng and dаyѕ to 75% mаturіty over environments. Highly significant variance observed due to hybrids in the pooled analysis for all the component traits indicating presence of considerable amount of variability among parents.

Mean squares due to genotype × environment revealed influence of environmental variation for all the traits under study except dаyѕ to 50% flowerіng, dаyѕ to 75% mаturіty, plant height, proteіn сontent, zinc content and iron content іn grаіns. Variance due to different environmental conditions exhibited differential response rate for all the component traits. 

With respect to Days to 50 % flowering, 13, 15 and 7 hybrids showed significant negative mid parent heterosis, better parent heterosis and standard heterosis, respectively over pooled basis (Table 2). The cross GW 322 × Raj 4238 exhibited the highest significant negative heterosis over mid-parent (-5.15%) and heterobeltiosis (-8.84%). Whereas the crosses GW 322 × Raj 4079 (-4.15%) and Raj 3765 × Raj 4079 (-4.15%) showed the highest significant negative standard heterosis. For Days to 75 % maturity, 11, 16 and 6 hybrids showed significant negative mid parent heterosis, better parent heterosis and standard heterosis, respectively over pooled basis. Heterosis in negative direction was desirable because it resulted in early maturity (Table 2). Similar findings were reported by Desale and Mehta (2013); Dhoot et al. (2020); Malav et al. (2020) in wheat.

Table 1: Pooled Analysis of variance (M.S.S.) for different characters in bread wheat (Triticum aestivum L.). 

*, ** Significant at 5% and 1%, respectively

With regards to plant height, 6, 17 and 18 hybrids showed significant negative mid parent heterosis, better parent heterosis and standard heterosis in desired direction, respectively over pooled basis. Cross Raj 4120 × Raj 4238 exhibited the highest significant negative heterosis over mid parent (-7.83%), over better parent (-15.20%) and over standard check (-15.06) (Table 2). Similar findings were also reported by Desale and Mehta (2013); Raj and Kandalkar (2013); Baloch et al. (2016); Thomas et al. (2017); Saren et al. (2018); Kumar et al. (2020); Malav     et al. (2020) in wheat.

The results for no. of effective tillers per plant demonstrated that 17, 8 and 2 crosses exhibited significant negative average heterosis, heterobeltiosis and heterosis over check, respectively (Table 3). The cross GW 322 × DBW 110 displayed highest significant  positive heterosis over mid parent (23.88%), over better parent (23.66%) and heterobeltiosis (16.30%) which is desirable in case of no. of effective tillers per plant. The findings for no. of grains per head and test weight indicated that 2 and 9 crosses displayed significant positive standard heterosis while 8 and 5 crosses showed significant positive heterobeltiosis in the desired direction. Cross Raj 4037 × Raj 4079 exhibited the highest significant positive heterosis over mid parent (11.50%), heterobeltiosis (10.43%) and standard heterosis (8.98%) for test weight (Table 3). These findings are in confirmation with Raj and Kandalkar (2013); Ismail and Samier (2015); Singh et al. (2016); Baloch et al. (2016); Rajput and Kandalkar (2018).  

In the study of grain yield per plant, 13, 10 and 5 crosses showed significant positive average heterosis, over better parent and over standard check, respectively. The cross GW 322 × DBW 110 displayed significant highest positive standard heterosis (11.71%) (Table 4). With respect to biological yield per plant, 12 and 8 hybrids showed significant positive mid parent heterosis and better parent heterosis, respectively over pooled basis. The cross Raj 3765 × Raj 4079 exhibited the highest significant positive heterosis over mid parent (9.34%) and heterobeltiosis (9.18%) (Table 4). With regards to harvest index, 12 and 2 crosses showed significant positive average heterosis and over better parent, respectively. The cross Raj 3077 × Raj 4079 displayed the highest significant positive heterosis over mid parent (18.45%) and heterobeltiosis (14.16%). Rahul (2017); Rajput and Kandalkar (2018); Kumar et al. (2020) also reported similar results in bread wheat. 

For protein content, 21, 18 and 5 crosses reported significant positive average heterosis, over better parent and over standard check, respectively (Table 5). The cross Raj 4037 × DBW 110 showed highest significant positive heterosis over mid parent (25.83%), heterobeltiosis (22.67%) and standard heterosis (8.60%). With regards to zinc and iron content, 10 and 14 crosses reported significant positive standard heterosis, respectively. The cross Sonalika × Raj 4238 showed highest significant positive heterosis over mid parent (29.76%) and heterobeltiosis (14.44%), while the cross Sonalika × DBW 110 displayed highest significant positive amount of standard heterosis (34.08%) (Table 5). Rahul (2017); Rajput and Kandalkar (2018); Kumar et al. (2020); Reddy et al. (2023) also reported similar results in bread wheat.

Table 2: Extent of Average heterosis, heterobeltiosis and economic heterosis for days to 50% flowering, Days to 75 % Maturity and Plant height (cm) in bread wheat (Triticum aestivum L.) on pooled basis.

*, ** Significant at 5% and 1%, respectively

Table 3: Extent of Average heterosis, heterobeltiosis and economic heterosis for No. of effective tillers per plant, No. of grains per head and Test weight in bread wheat (Triticum aestivum L.) on pooled basis.

*, ** Significant at 5% and 1%, respectively

Table 4: Extent of Average heterosis, heterobeltiosis and economic heterosis for Grain yield per plant, Biological yield per plant and harvest index in bread wheat (Triticum aestivum L.) on pooled basis.

*, ** Significant at 5% and 1%, respectively

Table 5: Extent of Average heterosis, heterobeltiosis and economic heterosis for protein content, zinc content and iron content in bread wheat (Triticum aestivum L.) on pooled basis.

The current study found that the majority of crosses had positive significant average heterosis, heterobeltiosis and standard heterosis for grain yield and key yield attributing traits, implying the dominance nature of genes with a positive effect. Furthermore, a number of crosses displayed favourable heterotic behaviour with negative heterosis for maturity-related attributes, indicating that the genes with negative effects were dominant for these characters. Thus, it can be concluded that the hybrids namely Raj 4037 × Raj 4238, Raj 3077 × DBW 110 and GW 322 × Raj 4079 were considered as the best heterotic hybrids for grain yield and attributing traits so these hybrids may be utilized to obtain desirable genotype.

The present findings based on heterotic performance of cross combinations could be used in future breeding programmes to create a good heterotic gene pool of wheat for boosting grain yield and other contributing attributes.