Wheat (Triticum aestivum L.) is a major crop grown in large irrigated as well as in rain fed areas. India, the second largest producer of wheat in the world has the greatest success stories of Green Revolution and has made rapid progress in food grain production during second half of the 20th century (Dhillon et al., 2010, Nagarajan, 2005). It accounts for approximately 12% of the world's wheat production and is the second largest wheat consumer after China. Wheat and its products play an increasingly important role in managing India's food economy. Wheat productivity depends upon the joint effects of numerous factors. The major challenge faced in modern crop production is maintaining crop yield under adverse stress and environmental conditions. Plants are frequently exposed to many stresses such as drought, low temperature, salt, flooding, heat, oxidative stress and heavy metal toxicity, while growing in nature. Fluctuations in environmental conditions initiate flexibility in normal metabolic processes, although every deviation of a factor from its optimum does not necessarily result in stress. Water deficit and salt stresses are global issues to ensure survival of agricultural crops and sustainable food production (Jaleel et al., 2007). Drought is perhaps the main factor limiting crop production world wide. It is a well known fact that drought limits plant growth and productivity more than any other single factor. Drought stress decreased amount of grain yield. Skipping any one of the stages, such as second, the third, the fourth, or the fifth irrigation stage caused a severe reduction in wheat yield during vegetative and early grain growth. Skipping the sixth irrigation stage during the late grain growth reduced the yield by 9.11%; whereas, reducing the amount of irrigation by 10% reduced the grain yield by 10.60% (Ouda et al., 2005). Plant height, spike lengths, grain number and total grain weight for well– watered and stress plants were compared by (Majer et al., 2008). Significant differences among cultivars and drought stress were found, with decrease in all traits as stress levels increased (Jajarmi, 2009). Water stress during different growth stages usually decrease final grain yield of wheat. During water stress leaves become smaller, which results in low leaf area index, low tillers/plant, as well as low shoot dry weight. The foliar spray of osmoprotectants has gained significant ground during the last decade, because it is a shotgun approach to improve stress tolerance in different crops. Benzylaminopurine (BAP) is also believed to be ideal for exogenous plant application because it is considerably more stable than natural CKs. It is readily taken up by the plant and not degraded by CK oxidase. The use of BAP promoted accumulation of dry matter. BAP promoted development of more leaf area and greater plant survival rates.

The crop was raised and treatments were allotted in split plot design. Each treatment was replicated thrice. The pre-sowing irrigation (75 mm) was applied, prior to sowing; the soil of the replications was carefully leveled to ensure even distribution of water. Water stress was imposed by stopping irrigation at the tillering stage and the boot leaf stage. Foliar spray of BAP at the vegetative stage was given at 60 DAS and at the reproductive stage was given at 90 DAS. At maturity ten plants of each variety per treatment (T₁–Untreated control, T₂ –Water-deficit at tillering stage (at 50% level using tensiometer), T₃– Water-deficit at boot leaf stage (at 50% level using tensiometer),T₄ –T₂+50 µg ml-1 BAP at vegetative stage, T₅-T₂+100 µg ml-1BAP at vegetative stage, T₆ –T₂+50 µg ml-1 BAP at vegetative and post-anthesis stage, T₇ –T₂+100 µg ml-1BAP at vegetative and 50 µg ml-1at post-anthesis stage, T₈ –T₃+50 µg ml-1 BAP at vegetative stage, T₉–T₃+100 µg ml-1 BAP at vegetative stage)were selected at random, tagged and labelled properly to record spike length, 1000 grain weight and harvest index.

Environmental stress especially drought stress can play an important role in the reduction of plant growth and development. Results revealed that maximum yield was achieved under full irrigation in both the genotypes as expected. From among the genotypes, PBW 343 had more yield as compared to the PBW 527 under control conditions. But under water stress, PBW 527 had higher yield as compared to the PBW 343. Pirayvatlou (2001) also reported that the high yielded variety were affected more under stress condition than the low yielded variety. Results also revealed that the water stress given at the tillering stage affected the yield more adversely than that of the water stress given at the boot leaf stage. Results signified that foliar application of BAP given at the vegetative stage had increased the yield in the genotypes studied at both the concentrations under stress conditions given at the stages (tillering and the boot leaf stage). But the higher concentration was found to be more efficient to increase the yield under tillering water stress. Spray of BAP at both the vegetative stage and the post anthesis stage showed significant increase in the yield under stress conditions. The results were even comparable to the control values. There was a significant effect of drought stress and genotype found in the size of peduncles produced. Water stress had significantly decreased the peduncle length in the studied genotypes (Table 1). Water stress significantly decreased peduncle length at all growth stages compared with unstressed control (Sangtarash, 2010). PBW 527 had longer peduncles under stress as well as under full irrigation conditions. The decrease was found to be more drastic when it was applied at the tillering stage as compared to the boot leaf stage. It ranges from 21.48– 19.00 cm and 24.26–27.74 cm in PBW 343 and PBW 527, respectively. Foliar application of BAP increased the peduncle length under stress conditions. The higher concentration of BAP (100 µg ml⁻¹) was more efficient when applied at the vegetative stage in the studied genotypes under boot leaf water stress (Table 1). PL/PH index was found to be higher in the PBW 527 as compared to the PBW 343. Under water stress there was a decrease in PL/PH index in PBW 343 as well as in PBW 527. The decrease in the PL/PH index under boot leaf stress was lower as compared to the tillering water stress in PBW 343. Similarly there was a decrease in PL/PH index when the water stress was applied at the boot leaf stage in PBW 527. Results showed that foliar application of BAP had increased the PL/PH index when it was applied under stress conditions (tillering and boot leaf stress). The value was found to be higher than that of the control values. Treatments which had provided water stress at the tillering stage and were sprayed with BAP at the rate of 100 µg ml⁻¹ at their vegetative stage showed increase in the PL/PH index in both the genotypes. Similar results were also found when stress was given at the boot leaf stage instead of the tillering stage. The values are more than that of the values of control.

Data depicted that PBW 343 had more seed weight per spike as compared to the PBW 527 under control conditions. Water stress had significantly decreased the seed weight per spike but the decrease was more pronounced in the PBW 343 when stress was given at the tillering stage. Water stress at the boot leaf stage had affected the seed weight per spike less adversely; drought stress results in reduced pollination and reduces the number of grains per spike and hence seed weight per spike. Grain yield was significantly decreased due to decrease in grain weight of each spike during the grain filling period under stress conditions. Grain weight per spike was significantly decreased by water stress particularly at the anthesis stage.

Presently foliar application of BAP at 60 DAS and 90 DAS has significantly increased the seed weight per spike under the stress conditions at both the concentrations. But the increase was more pronounced when it was applied at its higher concentration at the vegetative stage. When treatments were compared (T7), it was found to be a better treatment to increase the seed weight per spike. The increase in seed weight per spike was non significant when BAP was applied under boot leaf water stress at both 70 DAS and 100 DAS. The biomass production decreased with water stress in bread–wheat genotypes. Results showed that PBW 343 had more 100-seed weight as compared to the PBW 527 under full irrigation conditions. Water stress had decreased the 100-seed weight in both the genotypes, but the decrease was more pronounced in the PBW 343. More reduction was found in 100-grain weight under water stress at tillering stage as compared to boot leaf stage. Drastic decrease in 100-grain weight was recorded as the drought stress increased but highest reductions were found in terminal drought followed by post flowering drought (Qadir et al., 1999). Foliar application of BAP increased the 100-seed weight in both the genotypes under the stress conditions. However, the increase was more pronounced when BAP was applied at higher concentration (100 µg ml⁻¹) under water stress, which was given at the tillering stage in the studied genotypes. There was a significant increase in 10- seed weight when BAP was sprayed at its higher concentration during the vegetative stage as well as the post anthesis stage, that is, (T7) under tillering water stress.

From among the genotypes studied presently, PBW 343 had more number of spikes per plant as compared to the PBW 527 under full irrigation conditions. Number of spikes decreased when stress was given at the tillering stage as well as the boot leaf stage, but the water stress given at the tillering stage had significantly decreased the number of spikes. The effect of water deficits on the harvest index is complex due to the interactions between the timing and intensity of the stress relative to the developmental processes that determine the components of yield (Soriano et al., 2002). From among the genotypes studied presently PBW 343 had more harvest index as compared to the PBW 527 under both the stress as well as control conditions. Water stress had decreased the harvest index, but the decrease was more pronounced when the stress was given at tillering stage as compared to the boot leaf stage. Results revealed that foliar application of BAP had increased the harvest index when it was applied at its higher concentration (100 µg ml⁻¹) during the vegetative stage in the studied genotypes under stress conditions.

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