The six populations (parents, F1, backcrosses and F2) of the two wheat crosses, Gemmeiza
9 · IL1 (C1) and Sids 1 · IL2 (C2) were grown under normal irrigation (N) and drought stress
(D) at the farm of Faculty of Agriculture, Sohag University, Egypt to study the genetic background
of drought stress tolerance. Genetic variation was found for No. of spikes/plant (NS), 100-seed
weight (SW), grain yield (GY), biological yield (BY), relative water content (RWC) and chlorophyll
content (CC) under normal and drought stress environments in the two crosses. High heterosis was
observed for all studied characters under both water treatments in the two crosses except RWC and
CC in the first cross. Genetic analysis showed dominance in the inheritance of all studied characters
under both water treatments in two crosses except BY, RWC and CC under normal irrigation in
cross 1 and RWC under drought in cross 2 were controlled by the additive type of gene action. Narrow-
sense heritability in the two crosses ranged from 0.20 for GY (D) to 0.57 for CC (N) in C1. The
genetic advance in the two crosses was high (more than 40%) for GY (N&D), while NS, BY, RWC
and CC (N&D) were moderate (14–40%), indicating the importance of direct selection for these
characters. The genetic models fitted for NS, SW, BY, GY, RWC (D) and CC (D) in C1 and
NS, BY (N), GY, RWC and CC in C2 indicated dominance and additive · additive gene effects.
Both additive · additive [i] and dominance · dominance [1] effects were significant for NS, BY,
GY, RWC (D) and CC (D) in C1 and NS, BY (N), GY, RWC and CC in C2, supporting the
presence of duplicate type of epistasis. Since several important characters are influenced by
dominance and non-allelic gene interaction, it is advisable to delay selection to later generation with
increased homozygosity.