Effect of High Air Temperature on Grain Growth and Yields of Wheat Genotypes Differing in Heat Tolerance

Abstract

High temperature is one of the major environmental constraints limiting the grain yield of wheat in tropical and sub-tropical regions. To identify genotypes tolerant to thermal stress, ten wheat genotypes of different sources were tested in two temperature conditions in a Phytotron. An optimum temperature of 10 to 20 ℃ at night and 15 to 25 ℃ in the day was maintained in one glass room, whereas the temperature of another glass room was maintained 5 ℃ higher throughout the growing period of the wheat. Leaf photosynthesis, grain growth, relative yield performance and heat tolerance index were estimated following standard methods. The higher temperature enhanced plant growth, flowering and maturation. The grain growth rate was also higher at high temperature but it ultimately resulted in lower grain yield. The lower number of grain spikes-1 and smaller grain size that resulted from drastic reduction in grain growth duration were responsible for the yield reduction at high temperature. There were significant variations among the genotypes both for optimum and high temperature conditions. Based on the relative performance of yield and heat tolerance, three genotypes were identified as moderately tolerant to high temperature.