Differential response of wheat cultivars to terminal heat stress

Heat stress negatively influences the chlorophyll and grain filling processes in plants. Genotypes showing stay green character and better grain filling under heat stress are better able to cope with the heat stress. This study was aimed at knowing the mechanisms of heat resistance, during reproductive stages (booting stage, heading stage, anthesis stage and post anthesis stage) by monitoring the stay green character, water use efficiency, grain filling rate, grain filling duration, grain yield and harvest index of different wheat cultivars. For this experiment, seeds of wheat cultivars Chakwal-50, C-591, BARS-2009, Dharabi-2011, Sehr-2006, Shafaq-2006, Uqab-2000, Lasani-2008, Faisalabad-2008 and Mairaj-2008 were sown in 10 kg soil filled pots on November 25, 2011. The heat stress was applied at each respective reproductive stage, which continued till maturity. The heat stress was imposed separately at booting, heading, anthesis and post anthesis stages by placing pots in glass canopies with temperature of 4-5°C above than the ambient until maturity. Controlled pots were maintained under well watered conditions at ambient temperature. Heat stress at all the stages drastically reduced the performance of all tested wheat cultivars; severity being higher at booting and heading stages than anthesis and grain filling stages. Cultivar Mairaj-2008 stayed green and took more duration for grain filling, which resulted in the maintenance of grain weight and grain number per spike under stress conditions thus showing more grain yield and water use efficiency. In heat sensitive cultivars (BARS-2009, Shafaq-2006), the imposition of heat increased the grain filling rate with a substantial decrease in grain filling duration. Thus, stay green character and grain filling rate and duration under heat stress may be considered as selection criteria for developing new wheat cultivars for heat resistance during reproductive stages.