Evaluation of the 3rd Generation of Backcrosses and
its Parents of Two Bread Wheat (Triticum aestivum
L.) Cultivars for Drought Tolerance
Adel S Hadi and Dheya P Yousif*
Center of Plant Breeding & Genetics, Ministry of Science and Technology, Iraq
Submission: September 23, 2017; Published: May 24, 2018
*Corresponding author: Dheya P Yousif, Center of Plant Breeding & Genetics, Agricultural Research Directorate, Ministry of Science and Technology, Baghdad, Iraq, Email: firstname.lastname@example.org
How to cite this article: Adel S H, Dheya P Y. Evaluation of the 3rd Generation of Backcrosses and its Parents of Two Bread Wheat (Triticum aestivum L.)
Cultivars for Drought Tolerance. Agri Res & Tech :Open Access J. 2018; 16(3): 555988. DOI: 10.19080/ARTOAJ.2018.16.555988
Although drought stress has been well documented as an effective parameter in decreasing crop productivity in arid and semi-arid regions, developing and releasing new cultivars which are adaptable to water deficit can be a constructive program to overcome unsuitable environmental conditions. The present study was carried out to evaluate the performance of bread wheat genotypes in relation for yield and its components, biological yield, water use efficiency WUE, harvest index HI and stress susceptibility index (SSI) fewer than three of water irrigation regimes. The experiment was laid out in split plot based on a complete randomized block design, with three replications at the Center of Plant Breeding and Improvement at Al-Tuwaitha Research Station (30km southeast of Baghdad). Irrigation treatments (200,300 and 400mm as control) were considered as the main plots, whereas sub-plots were assigned of two bread wheat cultivars Rasheed and Baraka sensitive cultivars having good yield and quality and their two hybrids at fourth back cross hybridization; 643xRasheed, 649cx Baraka).
Results showed that grain yield and its component, decreased as the water amount decreased. Whatever, the biological yield behaved the same trends but the reduction differ from genotype to another, and the two hybrids showed less reduction in all characters mentioned above. Results also reveal that all genotypes, cultivars in addition to their hybrids differed in water use efficiency and there was significant difference among them. The hybrids (643xRasheed) and (649cxBaraka) exceeded in WUS of their parents and gave 1.837, 1.857Kgm-3, respectively under 200mm of water irrigation. Interpretation may related to the high grain yield (3675, 3715Kgm-3), respectively. The highest HI (33.49%) founded in the treatment of 200mm than the other two water irrigation treatments. The increase of HI in the 200mm of water irrigation was related to the decreasing biological yield under water deficit condition. Under 200 and 300mmof water irrigation treatments, the genotypes 643, 649c and their hybrids showed the lowest SSI values (<1), whereas cultivars Rasheed and Baraka gave more than 1SSI.The two hybrids gave the lowest values of SSI, especially under the drought stress (200mm) by 0.835, 0.813 for (643xRasheed) and (649cx Baraka),respectively. Significance differences for interaction between water irrigation supplies and genetic materials for WUE and SSI revealed the importance of diagnosing the genetic stability in further studies. Backcross (649cx Baraka ) gave the highest mean value for WUE (1.837Kg m-3 ) at 200mm in comparison with the other water supplies (1.367 and 1.111Kg m-3 for 300 and 400mm), respectively. The lowest mean value for SSI under the drought stress of 200mm were 0.835 and 0.813 for (643xRasheed) and (649c x Baraka), respectively.
Keywords: Triticum aestivum L.; Water irrigation supplies; Grain and biological yield; Water use efficiency; Harvest index
Drought is a major abiotic stress affecting global crop production. Many genes are involved in plant responses to drought, and some can be used for the improvement of drought tolerance by genetic engineering . Regulatory genes that activate or deactivate suites of drought responsive genes are of particular interest to biotechnologists [2-4]. Genes encoding dehydration-responsive element-binding (DREB) transcription factors (TFs) comprise one of the major groups of genes involved in drought response regulation . According to some estimates, almost 50% of wheat cultivated in the developing world
(50million ha) is sown under rain-fed systems, which receive less than 600mm of precipitation per annum. This rainfall could be as low as less than 350mm per annum in areas inhabited by the poorest and most disadvantaged farmers of the developing countries .
Wheat crop in Iraq affected by different types of biological and non-biological stresses during the growing season in almost all agricultural areas, regardless the crop irrigation methods. The scarcity of water during the planting season has become an obstacle to the cultivation of the first food security crop in
Iraq and despite the presence of the Tigris and Euphrates rivers;
planting of about 2 million hectares with wheat crop does not
exceed 2.5 million tons. The decrease in grain yields due to
drought conditions associated with a severe shortage of rainfall
during season, and other abiotic and biotic constraints .
Statistical data indicate that more than 65% of wheat
production comes from the northern region of Iraq. Although the
high percentage of wheat production, it faces two problems, 1)
delayed of rain fall season and 2) inadequate in most seasons.
The residual quantity of production (35%) comes from the
central and southern regions where irrigated agriculture suffers
from scarcity of water irrigation and all cultivars cultivated
in these areas are not drought-tolerant. Thus, each phase of
crop growth will be negatively affected relatively by drought.
For this purpose, elite and high yielding wheat cultivars that
are sensitive to drought may be used as recipient parents in a
backcrossing program involving drought-tolerant genotypes as
the male donor parent. In this study, conventional hybridization
and backcrossing were used to transfer-gene(s) from promising
moderate tolerant genotypes (643 and 946c) for local released
wheat cultivars (Baraka and Rasheed). The study includes the
following: investigation of the inheritance of constitutive and
inducible levels of transgenic expression in hybrid plants and
progeny during three consecutive backcrosses, (ii) evaluation of
the transgenic influence on development of the recipient cultivars
in the absence of stress, and (iii) confirmation of the transgenic
product functionality in backcross-derived lines by comparison
of (1) drought tolerance and (2) grain yields of control and trans
gene-containing plants under well-watered conditions and
under moderate drought stress at six growth stages.
Table 1 revealsthat the soil texture of the field experiment was
silt- clay loam with low organic matter content, 2.1 and 7.6 of Ec
and pH, respectively. After preparing the field by plowing, disking
and properly leveled it was divided into plots of (1.0×1.0m)
dimension which separated by a distance of 1/2m to prevent the
movement of water laterally. Two back crosses at BC3 seeds with
their parents (643, 649c, Rasheed and Baraka) were planted on
20 - 12 - 2015 for each water irrigation supply (400, 300 and 200
mm) under rainout shelter. The genotypes called 643 and 649c
were obtained from previous breeding program which practiced
hybridization among saber beg, the local cultivar, Mexipak and
the mutant R24 . However, about 70 experimental genotypes
were evaluated for drought tolerance and resulted the exceeding
the two indicated genotypes . Nitrogen fertilizer was applied
by the recommended dose of N (200Kg ha-1) during planting
and tillering (45 days after planting). Phosphorus fertilizer
was applied at the rate of 70kg of P2O5 ha-1 as the form of
superphosphate (16% P2O5) at planting  (Figure 1).
Literatures indicate that water consumption for wheat crop is
about 400-450mm during growing season. Depending of 400mm
as full irrigation (control treatment), 300mm as 2/3 of full
irrigation and 200mm as a half of full irrigation were practiced
with the six growth stages of crop during the growing seasons
(Table 2). Water irrigation applied according to the experimental
treatments by using flowed irrigation system, through line pipe
provide with meter gages for measuring water applied over
the growing season. Harvesting was on15of May 2016. All
measurements concerned with the number of tillers and spikes
per square meter, number of grains spike-1, 1000 grains weight,
grain yield (GY) and biological yield(BY) m-2 which converted
to kg ha-1, harvest index (HI),water use efficiency (WUE), stress
susceptibility index (SSI). Estimation for the traits above was as
Spikes m-2: Table 3 reveals that water deficit conditions
during the different growth and development stages were
decreased the number of spikes m-2. Water scarce decreased
spikes number by 11%, 19% in the 200 and 300 mm compared
to the 400mm (control). This result may due to the death of
some tillers carrying spikes. The highest negative effect of water
limitation was observed during the floral initiation (Booting and
anthesis stages). Previous similar results were reported by Adel
et al. ; Nazeri ; Robertson & Guinta  for wheat and
The number of the grain per spike is an important quantitative
trait as an essential grain yield component under drought and/
or good environment. Current results indicated that there was
significant difference among water irrigation supplies. Water
deficit caused decreasing of number of grain per spike by 10%,
11% for 200 and 300mm in comparison with control (400mm).
The booting to anthesis was the most susceptible period for grain
number per spike under water-limited condition, and could be
considered the most crucial growth and developmental stage for
the final grain yield. Results agreed with Al-Maeeny .
Although the number of grain spike-1 has a predominant
importance over grain weight with regard to grain yield, grain
weight is well documented to be a major yield component
determining final yield in Mediterranean environments .
Results in Table 3 indicated that water deficit in the 200 and
300mm water supplies were decreased the 1000 grain weight
by 9.8, 23.5% respectively compared with the control. The
most susceptible growth and developmental stage with regard
to 1000 grain weight is the anthesis to grain filling stage.
Researchers have reported that water limitation during grain
filling significantly decreased grain weight Nazeri , Slafer &
The results of the present study indicated that different
of water irrigation supplies during growth and development
stages had different considerable effects on grain yield (Table
3). There was significant difference among the water amount
on grain yield (4405Kg ha-1) which produced under optimum
water irrigation supply (control) whilst the lowest (3525Kg h-1) was observed in the lowest water irrigation supply (200mm).
Grain yield decreased by 10.5, 19.9 % for 300 and 200 mm
water irrigation supply, respectively compared with the control
(400mm). Reduction of grain yield may due to the drastically
decrease for one or more of yield component.
Table 3 showed that the biological yield decreased as the
water irrigation supplies decreased in 300, 200 mm by 16.6,
27.6%, respectively in comparison with control. There were
significant differences among the water irrigation supplies.
The highest biological yield (14350Kg ha-1) was produced
under optimum irrigation treatment (400mm) whereas, the
lowest (10524Kg ha-1) was investigated in 200mm.Result may
interpreted to the decrease the number of tillers per area unit.
Results agreed with Saleem , García Del Moral et al. , and
Krigwi et al.  for bread and durum wheat.
Data presents the average of all genotypes over three replications.
Harvest index is the proportion of grain yield to biological
yield and it shows the ability of the plants to translocation
physiological matters to grains. Table 3 showed that there was
significant difference among the three water irrigation supplies
on harvest index. The highest HI (33.49%) founded in 200 mm.
The increase of the HI in the lowest irrigation supply was due to
the decreasing of biological yield under water deficit conditions.
These results are concurrent with the findings of Al-Maeeny .
ȲP =Average yield of genotypes in the drought stress and
non- drought condition.
The experiment was laid out in randomized completely block
with split-plot design. Water irrigation supplies presents the
main plots and genotypes as sub plots with three replications.
Data were subjected to Analysis of Variance, and means were
separated by LSD at P≤0.01 using Gen Stat Statistical software
Results in Table 4 reflect the significant differences among
water irrigation supplies. Since, the highest water use efficiency
(1.762 Kg m-3) was observed at 200mm in comparison with the
other water supplies (1.314 and1.101Kg m-3 for 300 and 400mm).
The low water use efficiency for 400 mm may be attributed to
higher irrigation water use during growing season and on the
other hand, the increasable amounts of the evapotranspiration
and decreasing the net assimilation rate for all genetic materials
under investigation. Previous studies emphasized that moisture
stress affects water use efficiency for wheat . Oweis et al. 
for instance reported that water use efficiency varied from 0.66
to 1.34kg m-3 among different irrigation regimes. Table 4 showed
that all genetic materials under investigation differed in water
use efficiency and there was significant difference observed. The
backcrosses (643xRasheed) and (649cx Baraka) were exceeded
in WUE in comparison with their parents and gave 1.837 and
1.857kg m-3, respectively under drought stress of 200mm.The
high grain yield for wheat backcrosses (643xRasheed) and
(649cxBaraka) (3675 and 3715kg m-3), respectively caused to
increase the WUE and may due to the high productivity of its
recurrent parents cultivars. Results statistical analysis showed
that there was significance interaction between water irrigation
and genotypes in WUE ,wheat backcrosses (649cx Baraka) gave
highest mean value WUE1.837 Kg m-3 at 200 mm in comparison
with the other water supplies(1.367 and 1.111Kg m-3 for 300 and
Stress susceptibility index (SSI) were calculated on the
basis of grain yield for all genetic material under investigation
the three water irrigation supplies of irrigations. The backcross
(649cxBaraka) exceeded significantly with all genetic material
except the backcross 643xRasheed and gave the lowest SSI. With
the 200 and 300mm water supplies, the genotypes 643, 649c and
their backcrosses at BC3showedthe lowest stress susceptibility
index (SSI) values (<1.0) whereas, Rasheed and Baraka cultivars
had higher SSI and revealed values more than 1 (Table 4). The
two BC3 gave the lowest mean value for SSI, especially under the
drought stress (300 and 200m) which was 0.785 and0.785 for
(643xRasheed) and (649cxBaraka), respectively. These results
agreed with Khan & Naqvi  which they found that cultivars
with SSI was more than 1 which considered as water susceptible
and vice versa for the backcrosses that emphasize its tolerant
There was significance interaction between water irrigation
supplies and the genetic materials under investigation. The two
BC3 gave the lowest mean value for SSI under drought stress
of 200mm (0.835 and 0.813) for (643xRasheed) and (649cx
Baraka), respectively [24-29].
Although drought stress has been well documented as an
effective parameter in decreasing crop productivity in arid and
semi-arid regions, developing and releasing new cultivars which
are adaptable to water deficit can be a constructive program to
overcome unsuitable environmental conditions. The present
study indicated that it is possible to improve the drought tolerance
character in bread wheat by conventional backcrossing and
transferring genes which are responsible for drought tolerance
from moderate tolerance genotypes or cultivars to other having
high yields and good quality but sensitive to drought. Results
reflected the success in obtaining new genotypes with good grain
yield and tolerate drought in the targeted region. Bread wheat
cultivation in stressed environments which water irrigation
supplies not more than 200mm may present the relative solution
and solve the drought problem in Iraq. On the other hand, the
measurement of WUE and SSI were efficient parameters for
studying drought tolerance in wheat cultivars.
The authors would like to appreciate Dr. A. H. Hassan and
all the staff of the National Program for Wheat Development
Cultivation in Iraq for their assistance and supporting with
all essential requirements to success. Many thank for Dr. Al-
Hamdani for his cooperation and providing the drought tolerant
genotypes in this study.