NATURE OF GENE ACTION IN THE INHERITANCE

OF EARLINESS, GRAIN YIELD AND RELATED TRAITS IN DIALLEL CROSSES OF BREAD WHEAT UNDER DROUGHT STRESS AND NORMAL IRRIGATION

Rasha E. Mahdy

Agron. Dept., Fac. Agric., Assiut Univ., Assiut, Egypt

ABSTRACT

A half diallel set of crosses among seven wheat parents (Triticum aestivum L.) was conducted and evaluated in the F2-generation under drought stress and normal irrigation conditions. The reduction % caused by drought stress in the F2-populations was low for days to heading (DH) (2.55%) and harvest index ( HI) (1.05%), moderate for plant height (6.12%), spike length (8.89%) and 100 GW (6.64%), and high(15.53%) for number of spikes/plant (NS/P) and grain yield/plant (GY/P) (18.52%). Four promising F2-populations were obtained; "Om 2 x Sids 13" gave the highest GY/P under both of drought and normal irrigation environments (18.03 and 22.0 g), "Om3 x Sids 13" gave good yield under drought stress (16.13 g) and was responsive to good environment (normal irrigation) (20.33 g), "Om 2 x Om 3" and "Om 2 x Sids 4" gave good yield under drought stress and were responsive to good environment. The graphical analysis of Wr and Vr indicated that, the distribution of the parents around the regression line was not consistent for drought stress and normal irrigation, for plant height, NS/P and HI, and consistent for the other traits. The average degree of dominance was partial for all traits except for HI and 100 GW under drought stress, which showed complete dominance.The results indicated that both additive and dominance effects of genes were involved in the inheritance of all traits. The dominance variance "H1" was larger than the additive one "D" under both environments and"H1" increased under drought stress. Non-allelic gene interactions (epistasis) were involved in the inheritance of all traits except days to heading and plant height under normal irrigation. Earliness, NS/P and 100GW showed positive significant correlations with GY/P, therefore, these traits should be considered when selection practiced for GY/P in the promising populations of these materials either under drought stress or normal irrigation.These results suggest that pedigree and recurrent selection methods could be effective to improve new wheat lines from the above mentioned promising populations under both environments.

Keywords: Triticum aestivum L., Diallel analysis, Drought stress, DSI, Wr/Vr analysis, Gene action, Heritability

INTRODUCTION

Wheat (Triticum aestivum L.) is the most important food crop worldwide. It is grown on about 200 million ha in a variety of environments. The global wheat production is more than 600 million tons (Singh et al 2007). Wheat production in Egypt was 8.8 million tons in season 2013/14, and the annual consumption was about 19.5 million tons. The gab between production and domestic utilization (about 10.7 million tons) was met by imports (FAO, 2015).

Water stress is a major constraint in wheat production and affect 45% of wheat cultivated area worldwide (Andrew et al 2000 and Amjad et al 2011). In Egypt, there is an expected reduction in Nile water caused by the Renaissance Ethiopian Dam. Furthermore, the north seacoast and new reclaimed soils suffer from water deficit. To overcome the wheat consumption pressure of increasing population, the wheat breeders must concentrate their efforts to improve the yield potential of wheat by developing new high yielding varieties with desirable genetic makeup suitable to new reclaimed soil, and irrigated land.

The success of a breeding program to develop high yielding potential varieties for irrigated land, or tolerant to water deficit depends on precise estimates of genetic parameters for traits of interest. The combining ability analysis is a better biometrical approach to circumvent the plant breeding program (Baker 1978).

The diallel analysis provides unique opportunity to test number of lines and their cross combinations, and to identify the best parents and promising crosses for traits of interest. The research reports indicated contradictory results with respect genetic parameters controlling the inheritance of grain yield and its components. Darwish (2003), Riaza and Chowdhry (2003a and b), Joshi et al (2004), Dere and Yildirin (2006), Ul allahet al (2010), Yan et al (2011), Katta et al (2013) and Gomaa et al (2014) found that the additive type of gene action was more important than non-additive in controlling yield and its attributes. Otherwise, Bayoumi (2004), Farhat (2005), Saleh (2011), Mohamed et al. (2014), El-Hawary (2015), Abd El-Aty et al (2016), Baloch et al (2016), Saeed et al (2016) and Uzair et al (2016) found that the dominance variance was larger than the additive one for number of tillers/plant, spike length, grains/spike, grain yield and biological yield. Both of additive and non-additive gene effects were involved in the inheritance of yield potential, stress yield and several measures of drought resistance (Farshadfar et al 2011 a and b, and Farshadfar et al 2013). The objectives of the present study were to evaluate seven wheat genotypes with their F2-crosses under optimum and drought stress conditions, identify the promising F2-populations, and to study nature of gene action for earliness, yield and correlated traits, and phenotypic correlations among traits under both environments.

MATERIALS AND METHODS

Seven bread wheat genotypes (Triticum aestivum L.) were crossed in all possible combinations excluding reciprocals in season 2014/2015 at Fac. Agric. Exper. Farm, Assiut Univ., Egypt (Latitude = 27.178°, longitude = 31.185°). The seven parents are Egyptians, i.e., Omara 1(Om1), Omara 2(Om2), Omara 3(Om3), Sids 4, Sids 13, Misr 2 and Nilen. The first three lines were kindly delivered by Prof. M.Q. Omara (Dept. Genetics, Assiut Univ.). The lines Omara 1, Omara 2 and Omara 3 were advanced lines in the thirteen generation. In season 2015/2016, the parents and their F1-crosses were sown on December 10th 2015 in non-replicated experiment to obtain F2-seeds. In season 2016/2017, the seven parents and 21 F2-populations were sown on December 5th, 2016 in two separate experiments. The first experiment (normal irrigation) was irrigated five times in the whole season. The second experiment (drought stress) was irrigated two times in the whole season; the planting irrigation and another one three weeks later. The experimental design was a randomized complete block with three replications. The plot size was one row for each parent and two rows for each F2-population. The row was 3 m long, 30 cm apart and 10 cm between plants. The soil texture was clay. Super phosphate (P2O5, 15.5%) was added during land preparation at a rate of 23.25 kg P2O5/feddan (feddan= 4200 m2). Nitrogen fertilizer in the form the ammonium nitrate (33.5% N) was added at a rate of 80 kg N/feddan in one dose before the first irrigation. Weeds were controlled manually. Data were recorded on 20 guarded plants for each parent and on 50 plants for each F2-population in each replication. The studied characters were days to heading (DH), plant height (PH; cm), spike length (SL; cm), number of spikes/plant (NS/P), biological yield/plant (BY/P; g), grain yield/plant (GY/P; g), harvest index (HI%) and 100-grain weight (100 GW; g).

Drought susceptibility index (DSI) was performed as Fischer and Maurer (1978) formula. Yield of individual genotype (Yd) under drought, and under well-watered condition (Yw) were determined. Average yield of all genotypes under drought (Xd) and well-watered condition (Xw) were used to calculate drought intensity(D) as: D=1-Xd/Xw. The mean drought susceptibility index (DSI) of a genotype was calculated as = (1-Yd/Yw)/D. Analysis of variance was done on plot mean basis according to Steel and Torrie (1980). Mean comparisons were performed using revised LSD as outlined by El Rawi and Khalafalla (1980). The data were subjected to diallel analysis of F2 as developed by Hayman (1954 and 1958) and described by Mather and Jinks (1971).

RESULTS AND DISCUSSION

Means and variances

Means of the studied traits, reduction % and drought susceptibility index (DSI) are presented in Table 1. The genotypes (parents + F2-populations) mean squares was significant (P0.01) for all the studied traits (Table 2), indicating wide genetic variability.

Mean DH of the parents ranged from 80.33 for Sids 4 to 109.67 for Om 1 with an average of 94.38 under drought stress, and from 111.67 to 81.00 for the same respective parents, with an average of 97.76 under normal irrigation. Means of the F2-popultion were in the range of their respective parents under both environments, indicating partial dominance for DH, except one case (Om 2 x Nilen under drought stress) which showed over-dominance towards lateness. The latest parent (Om 1) tended to inherit lateness to its F2-poplations, and the F2-popultion of the earliest parent (Sids 4) tended to be early.

Table 1. Means of the studied traits, reduction% and drought susceptibility index(DSI) under drought stress and normal irrigation conditions.

Genotype / SL;cm / NS/P
Stress / Normal / DSI / Stress / Normal / DSI
Omara1 / 26.00 / 27.00 / 0.41 / 7.30 / 7.7 / 0.32
Omara2 / 13.00 / 15.00 / 1.48 / 10.20 / 11.50 / 0.71
Omara 3 / 11.33 / 12.67 / 1.17 / 8.30 / 10.70 / 1.40
Sids 4 / 14.67 / 15.33 / 0.48 / 5.90 / 10.20 / 2.63
Sids 13 / 11.67 / 12.00 / 0.31 / 10.50 / 11.30 / 0.44
Misr 2 / 10.67 / 12.00 / 1.23 / 7.30 / 7.60 / 0.25
Nilen / 9.00 / 9.67 / 0.77 / 4.60 / 5.50 / 1.02
Average / 13.76 / 14.81 / 0.79 / 7.73 / 9.21 / 1.01
Reduction % / 7.07 / 16.12
Om1x Om 2 / 15.00 / 16.33 / 0.91 / 8.40 / 9.50 / 0.72
Om1x Om 3 / 18.67 / 19.00 / 0.19 / 8.70 / 9.20 / 0.34
Om1 x Sids 4 / 21.67 / 22.33 / 0.33 / 7.80 / 8.60 / 0.58
Om1 x Sids 13 / 17.67 / 18.67 / 0.60 / 8.10 / 9.50 / 0.92
Om x Misr 2 / 17.00 / 20.67 / 1.97 / 7.20 / 8.50 / 0.96
Om1 x Nilen / 13.00 / 14.67 / 1.26 / 6.30 / 8.50 / 1.62
Om2x Om 3 / 13.33 / 14.33 / 0.78 / 8.70 / 10.00 / 0.81
Om2x sids 4 / 15.67 / 16.67 / 0.67 / 7.80 / 8.90 / 0.77
Om2 x sids 13 / 12.33 / 13.33 / 0.83 / 11.10 / 11.10 / 0.00
Om2 x Misr 2 / 12.67 / 14.67 / 1.52 / 8.80 / 10.30 / 0.91
Om2 x Nilen / 10.00 / 11.00 / 1.01 / 6.60 / 8.20 / 1.22
Om 3 x Sids 4 / 15.33 / 15.67 / 0.24 / 7.20 / 9.50 / 1.51
Om 3 x Sids 13 / 9.33 / 12.00 / 2.47 / 9.20 / 9.90 / 0.44
Oma 3 x Misr 2 / 10.33 / 11.67 / 1.27 / 9.50 / 11.20 / 0.95
Om 3 x Nilen / 11.00 / 11.67 / 0.63 / 6.90 / 8.00 / 0.86
Sids 4 x Sids 13 / 13.00 / 14.33 / 1.03 / 8.20 / 12.30 / 2.08
Sids 4 x Misr 2 / 12.33 / 13.33 / 0.83 / 7.50 / 9.10 / 1.10
Sids 4 x Nilen / 13.33 / 14.00 / 0.53 / 6.30 / 9.30 / 2.02
Sids 13 x Misr 2 / 10.67 / 12.67 / 1.75 / 8.20 / 9.90 / 1.07
Sids 13 x Nilen / 9.00 / 10.67 / 1.74 / 8.30 / 9.60 / 0.85
Misr 2 x Nilen / 12.33 / 13.67 / 1.08 / 7.30 / 7.90 / 0.47
Average / 13.51 / 14.83 / 8.00 / 9.48
Reduction % / 8.89 / 15.53
RLSD 0.01 / 1.70 / 1.468 / 0.2217 / 0.215
RLSD 0.05 / 1.28 / 1.104 / 0.1667 / 0.162

Table1. Cont.

Genotype / SL;cm / NS/P
Stress / Normal / DSI / Stress / Normal / DSI
Omara1 / 26.00 / 27.00 / 0.41 / 7.30 / 7.7 / 0.32
Omara2 / 13.00 / 15.00 / 1.48 / 10.20 / 11.50 / 0.71
Omara 3 / 11.33 / 12.67 / 1.17 / 8.30 / 10.70 / 1.40
Sids 4 / 14.67 / 15.33 / 0.48 / 5.90 / 10.20 / 2.63
Sids 13 / 11.67 / 12.00 / 0.31 / 10.50 / 11.30 / 0.44
Misr 2 / 10.67 / 12.00 / 1.23 / 7.30 / 7.60 / 0.25
Nilen / 9.00 / 9.67 / 0.77 / 4.60 / 5.50 / 1.02
Average / 13.76 / 14.81 / 0.79 / 7.73 / 9.21 / 1.01
Reduction% / 7.07 / 16.12
Om1x Om 2 / 15.00 / 16.33 / 0.91 / 8.40 / 9.50 / 0.72
Om1x Om 3 / 18.67 / 19.00 / 0.19 / 8.70 / 9.20 / 0.34
Om1 x Sids 4 / 21.67 / 22.33 / 0.33 / 7.80 / 8.60 / 0.58
Om1 x Sids 13 / 17.67 / 18.67 / 0.60 / 8.10 / 9.50 / 0.92
Om x Misr 2 / 17.00 / 20.67 / 1.97 / 7.20 / 8.50 / 0.96
Om1 x Nilen / 13.00 / 14.67 / 1.26 / 6.30 / 8.50 / 1.62
Om2x Om 3 / 13.33 / 14.33 / 0.78 / 8.70 / 10.00 / 0.81
Om2x sids 4 / 15.67 / 16.67 / 0.67 / 7.80 / 8.90 / 0.77
Om2 x sids 13 / 12.33 / 13.33 / 0.83 / 11.10 / 11.10 / 0.00
Om2 x Misr 2 / 12.67 / 14.67 / 1.52 / 8.80 / 10.30 / 0.91
Om2 x Nilen / 10.00 / 11.00 / 1.01 / 6.60 / 8.20 / 1.22
Om 3 x Sids 4 / 15.33 / 15.67 / 0.24 / 7.20 / 9.50 / 1.51
Om 3 x Sids 13 / 9.33 / 12.00 / 2.47 / 9.20 / 9.90 / 0.44
Oma 3 x Misr 2 / 10.33 / 11.67 / 1.27 / 9.50 / 11.20 / 0.95
Om 3 x Nilen / 11.00 / 11.67 / 0.63 / 6.90 / 8.00 / 0.86
Sids 4 x Sids 13 / 13.00 / 14.33 / 1.03 / 8.20 / 12.30 / 2.08
Sids 4 x Misr 2 / 12.33 / 13.33 / 0.83 / 7.50 / 9.10 / 1.10
Sids 4 x Nilen / 13.33 / 14.00 / 0.53 / 6.30 / 9.30 / 2.02
Sids 13 x Misr 2 / 10.67 / 12.67 / 1.75 / 8.20 / 9.90 / 1.07
Sids 13 x Nilen / 9.00 / 10.67 / 1.74 / 8.30 / 9.60 / 0.85
Misr 2 x Nilen / 12.33 / 13.67 / 1.08 / 7.30 / 7.90 / 0.47
Average / 13.51 / 14.83 / 8.00 / 9.48
Reduction% / 8.89 / 15.53
RLSD 0.01 / 1.70 / 1.468 / 0.2217 / 0.215
RLSD 0.05 / 1.28 / 1.104 / 0.1667 / 0.162

Table1. Cont.

Genotype / GY/p, g / HI / 100 GW, g
Stress / Normal / DSI / Stress / Normal / DSI / Stress / Normal / DSI
Omara1 / 11.03 / 11.90 / 0.40 / 35.33 / 35.67 / 0.93 / 3.68 / 3.90 / 0.81
Omara2 / 13.40 / 19.00 / 1.64 / 32.33 / 32.67 / 1.02 / 4.40 / 4.53 / 0.41
Omara 3 / 15.50 / 19.67 / 1.18 / 30.67 / 32.00 / 4.17 / 4.30 / 4.60 / 0.93
Sids 4 / 9.50 / 17.37 / 2.52 / 34.33 / 35.67 / 3.74 / 4.53 / 5.23 / 1.91
Sids 13 / 18.00 / 21.00 / 0.79 / 38.33 / 39.33 / 2.54 / 4.11 / 4.97 / 2.49
Misr 2 / 11.52 / 12.21 / 0.32 / 30.00 / 31.67 / 5.26 / 4.02 / 4.47 / 1.43
Nilen / 6.29 / 7.67 / 1.00 / 34.67 / 37.00 / 6.31 / 3.44 / 3.67 / 0.88
Average / 12.18 / 15.54 / 1.20 / 33.67 / 34.86 / 3.42 / 4.07 / 4.48 / 1.32
Reduction % / 21.66 / 3.42 / 9.21
Om1 x Om 2 / 11.53 / 14.13 / 1.02 / 34.00 / 33.00 / -3.03 / 3.80 / 3.97 / 0.60
Om1 x Om 3 / 12.50 / 15.33 / 1.03 / 33.00 / 33.67 / 1.98 / 4.07 / 4.37 / 0.98
Om1 x Sids 4 / 13.81 / 14.33 / 0.20 / 34.00 / 36.33 / 6.42 / 4.54 / 4.72 / 0.53
Om1 x Sids 13 / 14.74 / 16.67 / 0.64 / 35.29 / 35.67 / 1.05 / 4.33 / 4.63 / 0.92
Om1 x Misr 2 / 11.16 / 12.67 / 0.66 / 33.67 / 33.33 / -1.00 / 3.79 / 4.03 / 0.87
Om 1 x Nilen / 9.99 / 10.00 / 0.00 / 34.67 / 36.33 / 4.59 / 3.70 / 4.07 / 1.29
Om 2 x Om 3 / 14.81 / 18.67 / 1.15 / 34.33 / 33.33 / -3.00 / 4.40 / 4.70 / 0.91
Om2 x sids 4 / 14.03 / 17.73 / 1.16 / 35.33 / 34.67 / -1.92 / 4.40 / 4.77 / 1.10
Om2 x sids 13 / 18.03 / 22.00 / 1.00 / 34.67 / 37.00 / 6.31 / 4.22 / 4.43 / 0.70
Om2 x Misr 2 / 12.00 / 17.00 / 1.63 / 34.00 / 34.67 / 1.92 / 4.29 / 4.40 / 0.35
Om2 x Nilen / 12.00 / 14.00 / 0.79 / 33.33 / 36.33 / 8.26 / 3.89 / 4.43 / 1.75
Om 3 x Sids 4 / 11.90 / 18.07 / 1.90 / 32.67 / 34.33 / 4.85 / 4.50 / 4.97 / 1.33
Om 3 x Sids 13 / 16.13 / 20.23 / 1.13 / 39.00 / 38.00 / -2.63 / 4.20 / 4.51 / 0.99
Om 3 x Misr 2 / 16.00 / 16.10 / 0.03 / 32.33 / 32.33 / 0.00 / 4.23 / 4.65 / 1.27
Om 3 x Nilen / 9.69 / 13.10 / 1.45 / 35.00 / 35.33 / 0.94 / 4.30 / 4.60 / 0.93
Sids 4 x Sids 13 / 12.75 / 21.00 / 2.18 / 37.00 / 36.33 / -1.83 / 4.45 / 4.97 / 1.49
Sids 4 x Misr 2 / 12.99 / 16.47 / 1.17 / 34.69 / 34.33 / -1.05 / 4.53 / 4.77 / 0.70
Sids 4 x Nilen / 10.02 / 15.33 / 1.93 / 34.67 / 34.67 / 0.00 / 4.57 / 4.57 / 0.00
Sids 13 x Misr 2 / 12.63 / 14.23 / 0.63 / 36.00 / 35.67 / -0.93 / 4.21 / 4.79 / 1.73
Sids 13 x Nilen / 10.82 / 12.63 / 0.80 / 35.00 / 35.33 / 0.94 / 4.20 / 4.40 / 0.65
Misr 2 x Nilen / 10.29 / 9.00 / -0.80 / 33.00 / 32.67 / -1.02 / 3.98 / 4.17 / 0.66
Average / 12.75 / 15.65 / 34.55 / 34.92 / 4.22 / 4.52
Reduction % / 18.52 / 1.05 / 6.64
RLSD 0.01 / 0.51106 / 1.95703 / 1.9816 / 1.7073 / 0.141 / 0.166
RLSD 0.05 / 0.38437 / 1.47188 / 1.4901 / 1.2838 / 0.106 / 0.125

Reduction %= (normal-stress)/normal%

It could be noticed that, the effect of drought stress on the vegetative period was not strong, in which the reduction % was 3.46% for the parents and 2.55% for the F2-populations. This could be due to that the experiment was done in heavy clay soil of high water holding capacity. Drought susceptibility index (DSI) indicated that the parents Sids 4, Sids 13 and Misr 2 were tolerant to drought stress. The other parents were susceptible and recorded "DSI" more than unity.Drought susceptibility index of the F2-populations ranged from 0.0 (maximum resistance) to 2.43 (highly susceptible) for DH. Four out of the six populations of Sids 4, four and five for Misr 2 and Sids 13; respectively were tolerant. Furthermore, the population Om1 x Om2 (susceptible x susceptible) was tolerant (DSI =0.42), the population Sids 4 x Sids 13 (tolerant x tolerant) was highly resistant (DSI = 0.0), and Sids 4 x Misr 2 (tolerant x tolerant) was susceptible (DSI = 1.44). It could be concluded that, the drought tolerance respect DH in this set of diallel is a polygenic character, and its genes are distributed randomly among the studied parents.

Average plant height of the parents was 97.43 cm under drought stress, and 104.52 cm under normal irrigation. The tallest parent was Om 3 and the shortest one was Sids 4. Average PH of the F2-populations was 101.70 and 108.33 cm, under drought stress and normal irrigation; respectively. The reduction in plant height was 6.79 and 6.12% for the parents and F2-populations; respectively. The drought susceptibility index of the parents indicated that one parent (Om 2, DSI = 0.99) showed average susceptibility, and one parent (Om 3, DSI = 0.28) was tolerant to drought. However, 10 F2-populations were tolerant to drought in plant height and recorded "DSI" ranged from negative (Misr 2 x Nilen, and Om 3 x Sids 13) to less than one for the others. The tolerant F2-populations stemmed from average x tolerant, tolerant x susceptible and susceptible x susceptible parent, indicating unequal distribution of genes controlling tolerance among the studied parents.

Average spike length of the parents was 13.76 cm under drought stress and 14.81 cm under normal irrigation. The average spike length of the F2-populations was nearly like that of the parents under both environments. The reduction in spike length caused by drought stress reached 7.07% for the parents and 8.89% for the F2-populations. Mean spike length of the parents indicated that Om 1 showed the longest spike of 26.0 and 27.0 cm, and Nilen showed the shortest spike of 9.00 and 9.67 cm in both environments. One of the objectives of this study was to transmit the rachis of the long relax spike of Om 1 to the compact spike of the other parents. However, results of the F2-populations of Om 1 tended to show partial dominance to short spike of the other parents. None of the F2-populations showed long spike as Om 1 parent. On the other hand, the F2-populations of the other parents mostly showed partial or complete dominance towards the long spike parent. Drought susceptibility index of spike length indicated that the parents Om 2, Om 3 and Misr 2 were susceptible, and the other parents were tolerant. Eleven F2-population showed tolerance of spike length to drought, and three showed average tolerance. All the tolerant F2-populations, either have one or the two parents, were tolerant to drought stress for spike length.

Average number of spikes/plant was 7.73 under drought stress and 9.21 under normal irrigation. The lower NS/P was recorded for Nilen (4.6 and 5.5) under both environments, and the highest number was for Sids 13 under drought stress, and for Om 2 under normal irrigation. Reduction in NS/P caused by drought stress was 16.12% for the parents, and 15.53% for the F2-populations. The highest NS/P under drought stress was recorded for Om 2 x Sids 13 (11.10) followed by Om 3 x Misr 1 (9.50) and Om 3 x Sids 13 (9.20). Under normal irrigation, Sids 4 x Sids 13, Om 3 x Misr 2, Om 2 x Sids 13 and Om 2 x Misr 2 gave the highest NS/P.

Drought susceptibility index indicated that four parents (Om 1, Om 2, Sids 13 and Misr 2) were tolerant to drought respect to NS/P. Fourteen F2-populations showed tolerance to drought stress in NS/P. It could be concluded that, four out of the five superior F2-populations in NS/P were tolerant to drought stress (Om 2 x Om 3, Om 2 x Sids 13, Om 2 x Misr 2 and Om 3 x Misr 2) and showed drought susceptibility under less than unity.

Average grain yield/plant was 12.18 and 15.45 g for the parents, and 12.75 and 15.65 g for the F2-populations under drought stress and normal irrigation; respectively. The reduction reached 21.66% for the parents and 18.52% for the F2-populations. The highest yielding parent was Sids 13, and the lowest one was Nilen. The best F2-population was Om 2 x Sids 13 under both environments, and the lowest yielding one was Om 3 x Nilen under drought stress, and Misr 2 x Nilen under normal irrigation.

Drought susceptibility index of the parents for GY/P indicated that Om 1, Sids 13 and Misr 2 were tolerant to drought, and Nilen showed average tolerance to drought. Twelve out of the 21 F2-population were tolerant or average tolerant to drought stress in GY/P. The highest yielding ability population (Om 2 x Sids 13) showed average tolerance to drought stress. The other five high yielding populations; two of them (Om 1 x Sids 13, and Om 3 x Misr 2) were tolerant to drought, and the other three populations (Om 2 x Om 3, Om 2 x Sids 4 and Om 3 x Sids 13) were susceptible to drought, and recorded drought susceptibility index more than one. It could be concluded that, the best promising F2-population in GY/P Om 2 x Sids 13 gave the highest yield under both environments (18.03 and 22.00 g). However, Om 3 x Sids 13 gave good yield under drought stress (16.13 g), and responsive to good environment (20.23 g). Likewise, Om 2 x Om 3 and Om 2 x Sids 4 gave good GY/p under drought stress and responsive to normal irrigation (good environment).

Average HI of the parents was 33.67 and 34.86% and 34.55 and 34.92% for the F2-populations, under drought stress and normal irrigation; respectively. The reduction in HI was 3.42% for the parents and 1.05% for the F2-populations. The low reduction % in HI could be due to that the drought stress affected both of grains and straw. The highest HI was recorded for Sids 13, and the lowest was for Misr 2 under both environments. In the F2-populations, the highest HI was recorded for Om 3 x Sids 13, and the lowest was for Om 3 x Misr 2. Drought susceptibility index could be considered meaningless, because of low reduction %, and several F2-populations gave negative values. This is mainly due to that, the drought stress affected both of grains and straw.

Average 100-grain weight of the parents was 4.07 and 4.48 g, and was 4.22 and 4.52 g for the F2-populations, under drought stress and normal irrigation; respectively. The reduction reached 9.21% for the parents and 6.64% for the F2-populations. This could be due to that the pure lines in general are more sensitive to environments than heterozygous populations. Sids 4 gave the heaviest and Nilen gave the lightest grain weight under both environments. Means of the parents and F2-populations showed partial to complete dominance in most cases, and Sids 4 tended to inherit heavy grain to its progeny. Results of drought susceptibility index indicated that four parents (Om 1, Om 2, Om 3 and Nilen) were tolerant to drought, and 14 F2-population varied from resistant (Sids 4 x Nilen) to tolerant.

Abd El-Aty and Borhamy (2007) found that drought stress caused great reduction in all traits. Adel and Ali (2013), Abd El-Hady (2016) and Abd El-Aty et al (2016) came to the same conclusion. It could be concluded that the reduction% caused by drought stress in the F2-populations was low for DH (2.55%) and HI (1.05%); moderate for plant height (6.12%), spike length (8.89%) and 100 GW (6.64%), and high for NS/p (15.53%) and GY/p (18.52%). The promising F2-populations (Om 2 x Sids 13, Om 2 x Om 3, Om 2 x Sids 4 and Om 3 x Sids 4) were earlier in days to heading than the F2 average (except Om 2 x Om 3), had proper plant height, spike length, NS/P and 100 GW.