The experiment was carried out at the research field of the Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Salna, Gazipur from November, 2011 to March, 2012 on an upland soil. It is located at the center of Madhupur Tract (24?05' North latitude and 90?16' East longitude) at an elevation of 8.4 m above the sea level. The soil of the experimental field belongs to Salna series of Shallow Red-Brown Terrace soil type (AEZ 28) with silty clay texture in surface and silty clay loam in sub-surface region of the soil. The experimental site is situated in the sub-tropical region characterized by heavy rainfall during the months from July to September and scanty or no rainfall in the rest of the year.
Test Crop: Thirty-five wheat genotypes including most of the popular varieties, some advanced lines and some lines from abroad collected from Wheat Research Centre of Bangladesh Agricultural Research Institute, Nashipur, Dinajpur, Bangladesh were used in the present study.
Land Preparation: The land was well prepared by ploughing and cross-ploughing four times with a power tiller. Laddering was done for breaking the clods and leveling the lands. The various stubbles were removed by hand from the experiment field just before preparing the plot. The individual plots were prepared by making ridges (8 - 10 cm high) around the each plot to restrict the lateral run off of fertilizer with irrigation water.
Experimental Design and Treatments: The experiment was carried out in a split-plot design comprising two water regimes in main plot and 35 wheat genotypes were placed randomly in sub-plot with three replications. The water regimes were 1) Control (four irrigation were applied at crown root initiation, booting, anthesis and grain filling stages), and 2) Water deficit stress (irrigation was stopped after crown root initiation stage i.e. 20 days after sowing and the crop was protected from rainfall by rainout shelter). Thirty-five wheat genotypes including most of the popular varieties and some advanced lines collected from Wheat Research Centre (WRC) of Bangladesh Agricultural Research Institute (BARI), Dinajpur were Prodip, Shatabdi, Sourav, Gourab, Sufi, Kanchan, Seri, Pavon, Barkat, Balaka, Aghrani, Akbar, BARI Wheat 26, Protiva, Ananda, Bijoy, BARI Wheat 25, BAW 1151, BAW 1157, BAW 1158, BAW 1159, BAW 1160, BAW 1161, BAW 1162, BAW 1163, BAW 1164, BAW 1165, BAW 1166, BAW 1167, BAW 1168, BAW 1169, BAW 1170, BAW 1171, BAW 1172 and BAW 1173. The unit plot size was consisted of 6 rows each of 2.5 m long having a row to row distance of 20 cm. Operation Wheat seeds at the rate of 120 kg·ha−1 were sown in line by hand on November 24, 2011. Seeds were placed continuously in lines by making narrow and shallow furrows with iron rod and covered with soil by hand. After sowing of seeds light irrigation was given to ensure uniform germination of seeds. Fertilizers were applied @ 100-60-40-20-1 kg·ha−1 N-P2O5-K2O-S in the form of urea, triple super phosphate, muriate of potash and gypsum, respectively. Two-third of urea and total amount of other fertilizers were applied during final land preparation. The rest amount of urea was top dressed at crown root initiation stage (20 days after sowing) followed by first irrigation. Intercultural operations were done uniformly in each plot to ensure normal growth of the crop. Weeding and mulching were done simultaneously in the experimental plot for two times, firstly at 15 days after sowing (DAS) and secondly, at 35 DAS. Thinning was also done at 14 DAS.
Measurement of Canopy Temperature: Canopy temperature was measured with an infrared thermometer (Model THI-500, TASCO, Japan) at 12:30 pm on the day. The thermometer was held so that the sensor viewed only the canopy at an oblique angle above the horizontal; this position gave an elliptical canopy target and prevented the thermometer from sensing the soil surface when the leaves were rolled. All canopy temperature measurements were made five places in a plot and in a south facing direction to minimize sun angle effects as suggested by Turner et al.
Tolerance Indices: Stress tolerance and susceptibility indices including relative performance (RP), mean productivity (MP), geometric mean productivity (GMP), tolerance (TOL), stress susceptibility index (DSI), stress tolerance index (STI), and yield stability index (YSI) for water deficit environment were calculated based on grain yield under water deficit stress and control conditions.
Statistical Analysis: Recorded data were analyzed by statistically using the software MSTATC (Developed by the Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824 USA). Significance between treatments were tested by using least significant difference test (LSD) at p < 0.05 level.