GENETIC ANALYSIS OF WHEAT TOLERANCE TO DROUGHT UNDER DIFFERENT CLIMATIC ZONES.

Nine bread wheat (Triticum aestivum L.) genotypes with different characteristics were crossed in a half-diallel model in two different climatic zones in north and south Egypt (Kafrelsheikh and Toshka) during the two successive winter seasons 2017/18, 2018/19. Genotypes and their F₁-hybrids were evaluated under standard irrigation and drought stress conditions, to estimate heterosis of certain crosses for drought tolerance, and to pick out crosses useful in breeding programs for drought tolerance. The findings showed that substantial mean genotypes were found for all traits under various irrigation treatments as well as in the combined study. Means of all studied traits were decreased relative to nonstress environments. Highly significant differences were observed for general and specific combining ability for the studied traits under both irrigation treatments and in the combined analysis. The GCA/SCA ratio ranged from 0.31 in Kafrelsheikh and 0.80 in Toshka for No. of spike plant^-1 to 0.10 in Kafrelsheikh and 0.70 in Toshka for grain yield/plant, indicating that non-additive gene effects were more important than additive ones in the inheritance of all studied traits. The best general combiners were P₃, P₄ and P₈ for earliness in both locations and P₉ under Toshka conditions for grain yield/plant. The cross combination (P₅ × P₆) showed strong SCA effects for 1000-grain weight and (P₄ × P₇) days to heading. If crosses showing a high specific combination capability requires only one good general combiner, such combination will release desirable transgressive segregates providing that the additive genetic system present in a good combination and complementary epistatic effects present in the crosses will function in the same direction in order to minimize undesirable plant characteristics and to maximize the characters of the crosses. Therefore, several of the aforementioned crosses may be of primary importance in breeding programs under drought stress conditions. Thus, it may be suggested to carry on selection for water stress tolerance in Toshka to avoid effects of rain water and shallow water table in Kafrelsheikh zone. [ABSTRACT FROM AUTHOR]