Evaluation of the 3 rd Generation of Backcrosses and Its Parents of Two Bread Wheat ( Triticum aestivum L.) Cultivars for Salt Tolerance

: A field experiment was conducted during the winter season of 2017-2018 at the Center of Plant Breeding and Genetics, Al-Tuwaitha Research Station (30 km south east of Baghdad) to evaluate the performance of two bread wheat genotypes at the 3 rd backcross generation with their parents, cv. Furait, Barka and Iraq under saline field condition (12dSm -1 ). The objective of this study was to evaluate the beneficial effects of different backcrosses and its parents in targeted field condition, on grain yield and its components of bread wheat. Results showed that the two generations of (Furait x Baraka) and (Furait x Iraq) were significantly exceeded their parents and gave the highest values of spikes m -2 (207.0, 196.3), grain spike -1 (37.0, 39.0), 1000 seed weight (34.3, 33.3g) and grain yield m -2 (244.4, 242.7g), respectively. Phenotypic variation and the percentage of broad sense heritability for plant height, tillers m -2 , grains spike -1 , 1000 seed weight and grain yield m -2 were the highest compared with the value of environmental variation, and emphasized the important of genotypic variation and the ability to improve the desirable quantitative traits and reflects the high percentage of heritability.


Introduction
Plant growth and yield of bread wheat are seriously affected in salinity-prone environments, hence effective agricultural means are needed [17]. Bread wheat (Triticum aestivum L.) is amajor food crop all over the world, but annually increasable area are suffer from saline conditions [18]. Therefore, increasing salinity tolerance for wheat is necessary due to its moderate salt tolerance with EC threshold of 6-8 dSm -1 (60-80 mM NaCl) [4,9]. According to Francois et al. [6], wheat yield is decreased by 3% for each increased unit of EC on field level.
Salinity has affected the area cultivated with almost all crops all over the world [7]. High salt stress causes homeostasis change in water potential and ion distribution, molecular damage, growth inhibition and even death [32]. Salt stress adversely affects plant growth by osmotic stress, toxicity and nutrient deficiency [23]. Because of wheat crop importance, breeders are interested to develop this strategic crop for salt tolerance and associated mechanisms in candidate cultivars [27,28,15].
Identification of salt tolerance mechanisms led plant breeders to develop new cultivars are some of the most effective strategies for reducing salinity problems [2,22,24]. While the progress has not been so impressive, [3] screened many bread wheat cultivars for salt tolerance and summarized results of large international collections of wheat that have been screened by breeders in the hydroponic culture for wheat. Many Iranians were screened wheat accessions for grain yield at salinity condition in the field site in California [11] and no response for salt-tolerance. Hybridization is a useful tool for broadening the genetic variation within the crop species to estimate gene actions. [16] study on Lycopersicum is one of the first researches to evaluate the inheritance of salinity tolerance in a cross between Lycopersicom esculentum and L.pimpinelli folium 113 Dheya Buttrus Yousif et al.: Evaluation of the 3 rd Generation of Backcrosses and Its Parents of Two Bread Wheat (Triticum aestivum L.) Cultivars for Salt Tolerance which found that fruit yield in the hybrid was more affected by salinity than its parents. The objective of this study was to evaluate the beneficial effects of bread wheat backcrosses at salinity stress conditions with its parents.

Materials and Methods
A Field experiment was carried out during the winter season of 2017-2018 at Al-Tuwaitha Research Station (30 km southeast of Baghdad) Ministry of Science and Technology. Land prepared was practiced by plowing, disking and properly leveled and divided into plots of (2.0 × 1.5m). Two back crosses at BC3 generation for 2 wheat cultivars and its parents Furait (moderate salt tolerant), Baraka and Iraq sensitive local cultivars) for salt tolerance were planted on 15-12-2017 in the agricultural field (12 dSm -1) . The soil texture and its characterization showed in table 1. Nitrogen fertilizer was applied as recommended (200 N Kgha -1 ) during planting and tillering (45days after planting). Phosphorus fertilizer with 70 kgha -1 of P2O5 superphosphate (16% P2O5) was added at planting [12]. All backcrosses with its parents were introduced in a yield trial. Grain yield, its components and some growth traits were measured and data statistically analyzed by Randomized Complete Block Design with three replications. The phenotypic (σ 2 P), genotypic (σ 2 G) and environmental (σ 2 e) variances were estimated according to the method indicated by [29]. Data were subjected to analysis of variance and means were compared using LSD at P≤0.05 by Genstat statistical software computer (version2013) [5]. Broad sense heritability (H 2 B.S ) was estimated based on the ratio of genotypic variance to the phenotypic variance described by [26] which indicated that the heritability less than 40% considered as low, 40-60% was medium, and more than 60% as high.  Table 2 showed that there were significant differences (P≤0.05) among the backcrosses and their parent cultivars under investigation due to its wide genetic variation under investigation. The environmental impact of these traits and the susceptibility of the genes responsible for endurance starting its behavior for salinity tolerance effect. On the other hand, the backcrosses produced generation which superior to their parents due to the heterotic pattern caused by genetically unrelated parents. This result agreed with [21] who emphasized on the high level of genetic variation and the possibility of conducting genetic analysis of the properties and estimation of the components of phenotypic variation.

Plant Height
The effect of salinity stress on plant height was shown in Table 3. Plant height was significantly affected (P≤0.05) by salinity stress. All entries grown in salinity conditions were significantly affected and were shorter than the natural condition. Results obtained were agreed with [4,25]. The two back crosses exceeded its parents and gave plant length of 101.0 and 104.0 cm, respectively and agreed with the results found by [30]. Table 3 reveals that there were significant differences among the back crosses and its parents in the number of spike m -2 under the salinity stress. Significant superiority for the two back crosses than their parents and gave 207.0 and 196.3 spikes, respectively. Results agreed with [19,20].

Grain Spike -1
The number of the grain spike -1 is an important quantitative trait as an essential grain yield component under salinity and/ or good environment. Results in table 3 indicated that there were significant differences among the backcrosses and its parents in the number of grain spikes -1 exceeding of back crosses on their parents which gave 37.0 and 39.0 grain spike -1 , respectively. Results agreed with [10].

1000 Seed Weight
Although the number of grain spike -1 has predominant importance over grain weight with regard to grainyield, grain weight is well documented to be amajor yield component determining final yield in Mediterranean environments [30]. Table 3 showed that the two back crosses affected in 1000 grain weight and gave 34.3 g for (Furiat x baraka) and 33.3 g for (Furiat x Iraq). Results emphasized results of [1]. Table 3 revealed that there were significant differences among the back crosses and its parents on grain yield. The two back crosses (Furiat x baraka) and (Furiat x Iraq) significantly exceeded on its parents and gave 244.5and 242.7g m -2 . Results agreed with [31].  Table 4 showed the estimation of the bread sense heritability, phenotypic genotypic and environmental variances for all traits under investigation. Genotypic, phenotypic variability for grain yield m -2 (82.44) and (87.87) respectively were high in comparison with the low environmental variability (5.43) which reflects and explain the increase and high value of broad sense heritability. According to [13] heritability in broad sense plays an important role in deciding the suitability and strategy for selection of a character. Table 4 revealed that genotypic and phenotypic variability for spike m -2 , grain spike -1 and 1000 grain weight were 94.08, 78.86 and 78.37, respectively, which are considered as high in comparison with the low of environmental variability reflected in the grain yield (91.99 gm -2 ). The highest heritability values indicate that heritability may be due to higher contribution of genotypic component and thus suggested that selection could be practiced with high genetic advance [14]. This results showed clear indication of the importance of genetic improvement for raising the efficiency of back crosses and consistent with [8] when they explain the effect of gene function in the inheritance of most traits.

Grain Yield g Perm 2
Results suggest that there is a high potential for inheriting the salinity characterization using the back cross method sa covenantal breeding method to overcome the increasing problem of salinity in Iraq.

Conclusion
Although salinity stress has been well documented as an effective parameter in decreasing crop growth rate and seed productivity in soils affected salinity, developing and releasing new cultivars which are adaptable for salt tolerance can be a constructive program to overcome unsuitable environmental conditions. The present study indicated that it is possible to improve the salt tolerance bread wheat cultivars by conventional backcrossing programs and transferring genes which are responsible for salt tolerance from moderate tolerated genotypes or cultivars which with high grain yield and other good quality traits but sensitive to salinity. Results reflected the success in obtaining new genotypes with good grain yield and tolerate salinity in the targeted region.