Genetic Analysis of Yield and Its Attributes in Wheat ( Triticum aestivum L.) Under Normal Irrigation and Drought Stress Conditions

CLIMATE change and global warming cause an increase of drought effects on wheat production all over the world. Therefore developing wheat drought tolerant genotypes is essential, especially, under current water shortage. The present study was performed at the Experimental Farm, Faculty of Agriculture, Zagazig University, Egypt over winter seasons 2014/2015 and 2015/2016. Five diverse parental wheat genotypes (Misr 1, Gemmeiza 9, Gemmeiza 11, Line 1 and Line 2) were involved in a half diallel cross fashion under normal irrigation and drought stress conditions to investigate the effect of drought stress on yield and related contributing traits through mean performance, combining ability and gene action. The results showed significant differences among parental wheat genotypes and their F1 crosses as well as highly significant mean squares of general and specific combining ability for all studied traits under both conditions. For days to heading, Line 1 exhibited good level of earliness reflected in the performance of their F1 crosses (Line 1 x Misr 1) and (Line 1 x Line 2) under both conditions. The local wheat cultivars Misr 1 and Gemmeiza 9 as well as their F1 cross (Misr 1 X Gemmeiza 9) had high mean values for yield and its components under both conditions, reinforcing their importance in applied breeding programs. The parental wheat cultivar Gemmeiza 11 and F1 crosses (Line 1 x Gemmeiza 11), (Misr 1 x Line 2) and (Gemmeiza 9 x Gemmeiza 11) showed drought sensitivity index (DSI) values less than unity. Thus, these genotypes were considered as more tolerant to drought stress as regards to their grain yield/plant. The magnitude of additive (D) genetic component was higher as compared to their corresponding dominance (H1 and H2) ones, for days to heading both conditions and number of grains/spike under drought stress one, resulting (H1/D)0.5 less than unity. While, the dominance components was more than the corresponding additive one for flag leaf area, chlorophyll content, number of spikelets/spike, spike length, spike density, number of spikes/plant, 1000-grain weight and grain yield /plant under both conditions as well as number of grains/spike under normal irrigation only. The average degree of dominance was more than unity, confirming the importance of over-dominance in the genetic of these traits. under both conditions, the regression lines cut Wr axis above point of origin for days to heading, showing that partial dominance mode of inheritance for this character through additive gene action. On the other hand, it cuts Wr axis below origin for grain yield/plant, demonstrating that over-dominance gene effects are the prevailed type.