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Forty wheat varieties was evaluated for grain yield in the field for two successive crop seasons (2009–10 and 2010–11), with 2 dates of sowing, viz., early (last week of October) and late (first week of December). Based on the yield potential, five high yielding and five low yielding varieties were selected to study the relationship between grain yield and root characteristics along with canopy temperature depression (CTD) and flag leaf drying under early and late sown conditions. It was observed that under early sown restricted irrigation conditions the high yielding varieties utilized energy in increasing the root length and root density to deeper soil depths instead of accumulating root weight, compared to low yielding varieties. In contrast, under late sown condition, the high yielding varieties had more root weight and density in their upper soil depths, compared to low yielding varieties. Hence, it can be suggested to select wheat varieties with high root density and more root length in the lower depths of the soil for rainfed/restricted irrigation conditions to mitigate the early heat effects, and varieties having high root density and more root length in the upper layers of the soil for late sown conditions to tolerate the late or terminal heat. Further, high CTD scores at 1st stage (vegetative) and high leaf score at fourth stage (post flowering) were found to be important selection parameters, which help in reducing the evapo-transpiration and increase 1000 grain weight under early sown limited irrigation condition, and thereby increase the grain yield; whereas, CTD at 3rd stage (flowering stage) contribute to maintain the stay green trait for longer period and reduce the loss due to evapo-transpiration and in-turn increase the grain yield under late sown conditions. These traits can be used as selection tools for physiological breeding programme to increase the production and productivity of wheat.