Seedling Stage Heat Tolerance Mechanisms in Pearl Millet ( Pennisetum glaucum (L.) R. Br.)

Global climate change has raised threat to production of crops including millets that are grown in arid and semi-arid zones. Millets, in general and pearl millet which is one of the leading millet crops, withstand high temperature stress and reduced water availability during their life cycle as compared to other crops. Nevertheless, due to increase in soil temperature, the germination as well as seedling survival of pearl millet in farmer’s fields are drastically affected. Thus, study of mechanisms of heat tolerance during seedling stage leading to identification of tolerant genotypes is crucial. In our study, initially fifteen pearl millet genotypes were assessed for their germination pattern at higher temperature. Percentage of germination as well as radicle and shoot length were affected when the seeds were germinated at supra-optimal temperatures of 40 and 43°C. Five of the selected genotypes showed variation in the extent of membrane damage on exposure to high temperature as revealed by membrane thermostability assay. During heat stress, all these five genotypes, in general, had enhanced levels of ROS and activity of ascorbate peroxidase, enhanced production of compatible solute, glycine betaine and reduced chlorophyll a and b contents. Lipid peroxidation increased under stress in all genotypes but to a greater extent in the susceptible genotype, 01222B. Expression of hsp60 , hsp70 , hsp90 and TFA4b genes was higher than their respective controls in short-term and long-term heat stressed leaves. The relative expression of small HSP decreased as the duration of heat stress increased.