Indian Journal of Plant Physiology

Wheat (Triticum aestivum L.) cvs. HD 2285 and HD 2329 were grown in control (C) and heated (H) open top chambers (OTCs) for entire period of growth and development till maturity. In one set of OTCs, high temperature treatment was given only after anthesis stage. The mean maximum temperature of the entire period was around 3°C higher in H-compared to C-OTCs. Moderately high temperature differentially affected photosynthesis (Pn) in wheat cultivars. At anthesis, Pn of HD 2285 was more sensitive to elevated temperature than HD 2329, whereas, at post anthesis stage HD 2329 was more sensitive. The heat susceptibility index (S) for grain yield showed that HD 2285 is more susceptible than HD 2329 when moderate high temperature stress was given during entire period of growth and development. However, under moderate high temperature exposure after anthesis, the heat susceptibility index showed HD 2285 as stress tolerant and HD 2329 as a susceptible type. The greater susceptibility of HD 2285 than HD 2329 to moderately high temperature exposure during entire period of growth and development was due to greater reduction in tillers, consequently, ear number per plant in HD 2285. The study revealed that cv. HD 2285 tolerant to terminal high temperature would become susceptible when high temperature spells come during pre-anthesis period. There is a need, therefore, to develop wheat varieties which are tolerant not only to terminal high temperature stress, but to a warmer climatic condition.