Yield from genetic variability of bread wheat (Triticum aestivum L.) genotypes under water stress condition: A case study of Tandojam, Sindh

Water stress considered as a major abiotic factor limiting plant growth and affecting productivity is a serious global problem of Agriculture. To determine the effects of drought stress on various yield and yield associated traits of bread wheat. Fifteen newly evolved genotypes and two check varieties viz., NIA-Amber (drought-sensitive), Khirman (drought-tolerant) were selected for various water stress under field observations. Experiment was conducted in split plot design using three treatments viz., single irrigation, two irrigations three irrigations. The test entries comprised of 11 exotic wheat genotypes (BWDYT-1 to BWDYT-11), two mutant lines (MASR-18 and MASR-64) developed through radiation-induced mutations, two doubled-haploid lines (DH-3/25 and DH8/13). The effects of water stress were determined on different phenological traits viz., days of booting, days of heading, grain filling period, days to maturity, and morphological yield associated traits viz., plant height, tillers per plant, spike length, grains per spike, main spike yield, seed index, and the grain yield per plot. Ten plants per replication/genotype and treatments were randomly selected to record the data. Result revealed that the genotypes, treatments, and genotype × treatment interactions were highly and significantly (P≤0.01) different with each other for most of the traits. However, the genotypes performed differently and variably with each other under water stress conditions imposed at various growth stages. Wheat genotypes BWDYT-2, BWDYT-3, BWDYT-4, and MASR-64 showed earlier maturity and could be more suitable under stress conditions. Genotypes BWDYT-1, BWDYT-5, BWDYT-6, BWDYT-8, BWDYT-10, BWDYT-11, MASR-64, DH3/25, and DH8/13required more days for grain filling period at T1; could be considered as tolerant.


Introduction
Water stress is a major factor affecting about 31.5% of 99 million hectares of developing countries, and at least 60 million hectares of wheat are cultivating in these area [1]. Therefore, improving the quality and quantity of crops is the central goal of agriculture research. Adding to its soil physical and chemical properties, and the absorption of nutrients can be enhanced by humic acids to improve root health that consequently increase plants yield [2]. Several areas around the world encounter water shortage during wheat growing season. Understandably, the world population is increasing very fast particularly in developing countries and ultimate increase of food supply is parallel such increase of food demands can be fulfilled from rain-fed areas [3].
[M1]The first citation should be number one and the next citation should be the next number Wheat (Triticum aestivum L.) is a staple food and the major cereal grain crop in the world, including Pakistan. Wheat is the second major crop cultivated throughout the temperate and tropical regions of the world. It provides more than 50% of the total calories and 60% of the total protein consumed by the population as a whole. Being the member of grass family, wheat dominates world agricultural production, because it directly or indirectly provides a large proportion for the human diet [4]. It contributes 10.6 percent to the value added in agriculture and 2.6% to grass domestic production. Nevertheless, number of studies have been documented on wheat under water stress tolerance globally. Water stress tolerance level varies from species to species or even within species [5] stated that water deficit and salt stress are global problems that affect the survival of agricultural vegetation and sustainable meals manufacturing. Water stress tolerance is to be considered as main breeding target in evaluating the crop performance under water deficit conditions [6]. The plant response to drought can be studied by identification of traits related to drought tolerance at the morphological, physiological, and biochemical levels [7,8]. The water stress is the most important environmental cause major losses to the crops and can decrease grain yield, therefore approximately 17 to 70% grain yield losses have been reported [9]. Therefore, understanding selection of the biochemical and physiological origin of water stress tolerance in plants is essential for crops breeding [10]. Wheat is the most important cereal crop of the world and major staple food crop of Pakistan. Grain yield is the polygenic complex character governed by the genotype, environment and genotype x environmental (GxE) interaction. Pakistan ranked in top10 wheat producing countries of the world [11]. However, the appropriate yields are not being obtained due to biotic (diseases and pests) and abiotic stresses which includes shortage of irrigation water (drought), heat stresses and the salinity [12]. The identification of new ideotypes possesses tolerance to water stress conditions is the one way to minimize the yield gap. These all environmental stresses, water stress is the main environmental constraints such as hot and dry weather limiting the crop productivity of wheat. Due to very rare rainfalls in the in generally country and particularly in Sindh, there is acute scarcity of the irrigation water in the canals especially during rabi crop season. The development of germplasm endowed with better tolerance to such biotic and abiotic stresses through various breeding techniques is one of the main objectives of the plant breeding. The identification of new ideotypes possesses tolerance to water stress conditions is the one way to minimize the yield gap. Keeping in view the shortage of irrigation water, the experiment was conducted to estimate the effects of water stresses on various yield and yield associated traits and to select the potential wheat genotypes for future breeding. The current study was conducted to screening out the 17 genotype of wheat under water stress condition at different growth stages from seedling to maturity to see the effects of water stress on phenological and morphological traits among the varieties. The findings of wheat genotypes under water stress conditions enable to provide information regarding the diversity of new elite germplasm and their performance in severe environments effects of water stress on cultivar at different growth stages.

Plant height (cm)
Height of plant showed significant difference for wheat genotypes among three treatments (P<0.05). T3 (100.44cm). Significant increase in plant height was compared to T1 and T2 (91.82 and 96.0cm) respectively. Highly significant differences (P<0.05) for the trait of plant height were recorded in wheat genotypes at T1 (

Discussion
The effects of water stress during various critical growth stages were determines on early growth vigor, early ground cover, plant height (cm), spike length (cm), spikelets spike -1 , grain spike -1 , main spike yield (g), tillers plant -1 , days to booting, days to heading, days to maturity, days to grain filling period, peduncle length (cm), biological yield plot -1 (g), grain yield plot -1 (g), harvest index (%) and 1000-grain weight (g). Data recorded on various traits were statistically analyzed. The results indicated that the genotypes, treatments and genotype x treatments interactions were highly and significantly (P ≤0.01) different among other for different yield associated traits; which indicated the genetic diversity among the genotype. Genotypes performed differently and variably with each under water stress conditions imposed at various growth stages. The visible effects of environments over genotypic performance for most of the traits were also observed. A trivial number of genotypes perform exclusively under sever water stress conditions while other could not compete.
Significant effects of water stress were observed on early growth vigor, plant height, number of spikelets spike -1 , main spike yield, number of tillers plant -1 , days to booting, days to heading, grain filling period and peduncle length, whereas, nonsignificant differences were observed in genotypic mean squares for the traits early ground cover, spike length, number of grains spike -1 , days to maturity, biological yield plot -1 (g), grain yield plot -1 (g), harvest index (%) and thousand grains weight (g). Also noted the yield potential of wheat genotypes under drought condition. The various studies reported that the water stress imposed at different growth periods during booting, heading and early grain filling stage significantly reduces the grain yield. Days to maturity Days to maturity, is considered to be the main factor in achieving appropriate yields and the early maturing genotypes are supposed to be more suitable under stressed or harsh environments [15]. Such genotypes have capability to escape from severe water stress and mature earlier.

Plant Height (cm)
The visible effects of different water stresses were recorded on plant height of wheat genotypes. Various genotypes showed less reduction in their plant height as compared to other genotypes at T1 (single irrigation). At T1, genotypes BWDYT-1, BWDYT-5, BWDYT-8, BWDYT-11, MASR-64, and DH8/13 showed significantly reduced their height which indicated the tolerance of genotypes to water stress environment. Two time irrigated (T2), new genotypes BWDYT-11 and MASR-64 showed less reduction in plant height. The minimum and maximum reductions in cultivars for plant height categorized first group as drought tolerant and second as susceptible ones. According to [17] who noted that withholding irrigation at booting and at anthesis stages caused significant reduction in wheat plant height. Plant height directly or indirectly contributes towards grain yield, yet it could serve as an important indicator of waterstress tolerance via normal or retarded plant height.

Tillers plant -1
The trait number of tillers plant -1 is the main yield contributing trait. Wheat genotypes BWDYT-1, BWDYT-7, BWDYT-9, DH3/25) and a check variety NIA-Amber showed more number of tillers plant -1 at T1 (single irrigation). [18] Found the visible effects of water stresses on tiller number of wheat genotypes. Spike length (cm) Five wheat genotypes BWDYT-1, BWDYT-8, BWDYT-10, DH3/25 and DH8/13 showed less reduction in spike length at severe stress (T1); could be more tolerant to water stress conditions. The significant correlation between spike length and grain yield in stress condition and reported that the ability of swing nitrogen in spike and ability of retransforming of it to seed is effect. However, in our studies spike length of genotypes were affected due to water stress. Water stress at stages before anthesis can reduce number of kernels ear -1 [19]. Grain spike - 1 The mean performance for grains spike -1 of all wheat genotypes BWDYT-1, BWDYT-3, BWDYT-4, BWDYT-5, BWDYT-7, BWDYT-8,and DH3/25 along with check variety Khirman reduced number of grains per spike -1 at higher stress (T1). These findings suggested that these genotypes could be selected or further confirmed for drought tolerance studies. Drought stress before the anthesis in spring wheat also reduces the number of grains spike -1 [20]. Main spike yield (g) Wheat genotypes showed different response for the trait main spike yield at various water stress conditions. Genotypes BWDYT-1, BWDYT-2, BWDYT-4, BWDYT-5, BWDYT-6, BWDYT-7, BWDYT-8) showed increase in main spike yield at T1 as compared to all other entries and local checks; might be less affected due to water stress. Similar findings were also reported that identifying the genotypes which have high further transfer ability in drought stress condition especially in grain filling stage provides the possibility to increase yield of grains without any increase in the amount of consumed water [21].

Conclusion
It is concluded that water stress significantly impact on yield and associated traits. The advanced genotypes BWDYT-1, BWDYT-2, BWDYT-3, BWDYT-6, BWDYT-8, BWDYT-9, BWDYT-10, BWDYT-11, MASR-18, MASR-64 and DH8/13 and both the standard/ controlled varieties Khirman and NIA-Amber produced significantly the highest grain yield than other contesting genotypes under sever water stress conditions (single irrigation). These genotypes showed genetic improvement in various yield traits as compared to high yielding and high tillering variety NIA-Amber and droughttolerant variety Khirman which were used as standard or check varieties. Therefore, our finding suggested that these genotypes had potential to grow under stress condition as compared when to other genotypes. Moreover, analyzed wheat varieties under water-stressed environments and screening through this study are selected as droughttolerant genotypes for future breeding to enhance yield in drought areas.