Gene Action and Combining Ability of Cellular Thermotolerance in Bread Wheat (Triticum aestivum L.)

Heat stress is one of the most important factors limiting growth and productivity of wheat. In the present study, gene action, general (GCA) and specific (SCA) combining ability of cellular thermotolerance were studied in a nine-parent half diallel cross of bread wheat evaluated under normal (1{^st} sowing date) and heat stress (late sowing date) conditions. The cellular thermotolerance was estimated based on cell membrane thermostability (CMS) and tetrazolium chloride (TTC) reduction. Grain yield/plant (GYP), 1000-kernel weight (TKW), stem diameter (STD) and heat tolerance index (HTI) were measured. Compared with their parents, F1 hybrids significantly produced higher GYP, CMS, TTC and HTI. Highly significant mean squares of GCA and SCA effects were observed for all traits with GCA mean squares being much larger than that of SCA. Highly significant additive (a) and non-additive (b) gene actions were observed for all the traits with a predominance of the additive gene actions. However, the dominance genetic variance of CMS and TTC was greater than the additive variance. Moderate to high narrow-sense heritability was obtained for CMS (0.52), TTC (0.57) and HTI (0.71). GYP was significantly correlated with CMS (r = 0.62), TTC (r = 0.63) and HTI (r = 0.60). A highly significant positive correlation was obtained between CMS and TTC (r = 0.73), supporting that CMS and TTC could be used as efficient criteria for selecting wheat genotypes under heat stress. The parents P9, P1 and P2 were identified as best general combiners for CMS, TTC and HTI respectively. Six crosses were identified as best promising combinations for CMS (P1 × P8 and P5 × P9), TTC (P4 × P9 and P5 × P6) and HTI (P1 × P2 and P8 × P9). Thus, inclusion these superior genotypes into breeding programs could be useful for improvement of heat tolerance in wheat.