Thermotolerance of pearl millet and maize at early growth stages: growth and nutrient relations

Thermotolerance of pearl millet (Pennisetum glaucum cv. ICMV-94133) and maize (Zea mays cv. Golden) was assessed at germination and vegetative stage. Final percentage of germinated seeds and rate of germination ( number of days to 50% germination) decreased due to high temperature (45degreesC) similarly in the both species. In contrast, at the vegetative stage, high temperature (38/27degreesC) caused a significant reduction in shoot dry mass of maize, whereas this attribute remained almost unchanged in pearl millet. Relative growth rate and net assimilation rate (NAR) increased significantly in pearl millet due to high temperature, but in contrast, in maize NAR was slightly reduced. Concentrations of N, P, and K in the shoots of both species increased at high temperature, but N accumulation was more pronounced in pearl millet than in maize. High temperature caused a marked increase in both shoot and root Ca2+ concentration in maize, but it did not affect that of pearl millet. S concentration in the shoots of maize decreased significantly due to high temperature, whereas that in pearl millet remained unaffected. Shoot Na+ concentration of both species was not significantly affected by high temperature. High temperature caused a significant increase in uptake of N, P, and K+ in pearl millet, but the uptake of Ca2+, Mg2+, Na+ and S remained unaffected in this species. In contrast, in maize, a significant increase in uptake of K+ and Ca2+, and a decrease in uptake of N, S, Mg2+, and Na+ were found at high temperature. Overall, maize showed lower tolerance to high temperature compared with pearl millet.