JIA-2019-11

2484 Hafiz Ghulam Muhu-Din Ahmed et al. Journal of Integrative Agriculture 2019, 18(11): 2483–2491 be adopted more than one tolerance mechanisms at a time of drought. In that regard, there are three fundamental mechanisms which a plant can acclimatize to manage with the water shortfall: (i) Escape, (ii) avoidance or tolerance, and (iii) resistance mechanisms (Waqas et al . 2013: Ahmed et al . 2017). In escape mechanism, plant finalizes its life cycle in advance the water deficit. In tolerant mechanism, plants take paces to get by with water shortage conditions, e.g., closing of stomata, reducing the rate of transpiration in the plant body. In drought resistant mechanism, plant proceeds phases against water deficit condition by the upkeep of the photosynthetic pigments and maintains root- to-shoot ratio for effectively portioned the whole assimilated (Ashfaq et al . 2016). Vigorous seedling is imperative in defining the yield of plant in short period of time (Noorka and Khaliq 2007). A genotype with drought stress tolerance has more impenetrable rooting facilities to boost the preoccupation of soil moisture and reduces the special effects of water shortfalls during development and growth (Zhong and Wang 2012). Root, the prime portion of wheat plant, is influenced primarily by drought. Lengthy roots confirm the accessibility of moisture from the deepness of the soil and assure the adaptation in drought stress environments. Length of root at the primary stages of the plant is important traits for enhancing yield under rain-fed environments (Shabazi et al . 2012). According to these scientists, growth of wheat seedling is affected under water deficiency conditions, but the effect is different from genotype to genotype. Selection of genotypes with better performance during drought stress conditions could rise the production of rainfed areas (Noork and da Sileva 2012; Waqase et al . 2013). Selection of genotypes on the basis of seedling attributes is easy, cheap, and less laborious. Similarly, seedling indices reveal moderate to high variability with additive types of gene action across environments (Waqas et al . 2013; Ahmed et al . 2018), thus have an advantage of effective screening at primary stage. Reduced or unaffected chlorophyll contents under water shortage conditions have been described in various species, provisional on the period and intensity of drought stress. The level of chlorophyll contents alters during drought conditions. The carotenoid play vital roles and benefit for plants to resist water shortage stress (Jaleel et al . 2009). Drought stress prevents the synthesis of chlorophyll a / b and declines the binding proteins, leading to decrease of the light-harvesting pigment protein allied with photosystem II (Anjum et al . 2011). The possessions of drought stress on chlorophyll and carotenoid levels have been examined in various major field crops. The succeeding experiment was directed for screening of 105 miscellaneous wheat accessions for drought tolerance on the basis of seedling attributes and to define the link of studied seedling indices under normal and water stress environments. This will provide a theoretical basis of drought resistance abilities for dryland farming in the semiarid and rainfed regions. 2. Materials and methods 2.1. Experimental design Experiment was planted using 15 cm×15 cm sand filled polyethylene bags in the screen house of the Plant Breeding and Genetics, University of Agriculture Faisalabad, Pakistan following completely randomized design under factorial with three replications in normal and water stress environments. 2.2. Experimental materials The experimental material consisted of 105 spring wheat genotypes (Appendix A). Two seeds per polyethylene bag were sown and thinned to one seedling per bag after germination. Five bags per genotype were used for each replication. One set of genotypes has been regularly irrigated (100% of field capacity) while the other set of same wheat genotypes was kept under water deficient stress (at 50% field capacity) after application of watering on sowing. The field capacity (FC) of the soil used in the experiments was calculated with pressure membrane chamber apparatus (Gugino et al . 2009). 2.3. Studied parameters Data of the shoot length, root length, chlorophyll a and b , and carotenoid contents were measured from 3-wk-old wheat seedlings from both environments. The chlorophyll a and b were measured by using the following formula (Lichtenthaler 1983; Lohithaswa et al . 2013): Chl a (mg g –1 )=[12.7×(OD 663 )–2.69×(OD 645 )]×V/1000×W Chl b (mg g –1 )=[22.9×(OD 645 )–4.68×(OD 663 )]×V/1000×W where V, volume of extract; W, weight of fresh leaves; OD, optimal density. The carotenoid content was calculated by using following formula (Robbelen et al . 1957): Carotenoids=Acar/EM×100 where the unit of carotenoids is mg g –1 fresh weight, Acar=[(OD 480 )+0.114×(OD 663 )]–0.638×(OD 645 ), Em=2500. 2.4. Statistical analysis Scored data were exposed to analysis of variance (ANOVA) technique (Steel et al . 1997). Those characters displayed significant differences between studied genotypes were