Journal of Agrometeorology 21 (3) : 241-248 (September 2019) Effect of elevated temperature regimes on growth and yield of rice cultivars under temperature gradient tunnel (TGT) environments * PRABHJYOT KAUR , HARLEEN KAUR, HARPREET SINGH and S.S. SANDHU Department of Climate Change and Agricultural Meteorology, Punjab Agricultural University, Ludhiana - 141004, Punjab, India * Corresponding author: prabhksidhu@gmail.com ABSTRACT The effect of elevated temperature on rice were studied during kharif 2013 and 2014 using six cultivars of rice (PR-116, PR-118, PR-113, PR-115, PR-121 and PR-122) with two replications within a temperature gradient tunnel in which temperature was elevated from the ambient level (+4.5, +5.0, +5.3, +5.5 and +5.8 °C) for the entire crop growth period. The results revealed that the plant height increased under elevated temperature regimes, although the rate of change varied with cultivars as well as the stages of the crop. Amongst the six cultivars, the plant height was maximum for cv PR-118 (13.9 cm in vegetative stage (VS) and for cv PR-113 (58.5 cm in grain development stage (GDS) and minimum for cv PR-121 (12.4 cm in VS and 51.8 cm in GDS). The overall tiller number under elevated temperature regimes was maximum for cv PR-122 followed by PR-121, PR-113, PR-116, PR-115 and PR-118 in decreasing order. The 1000-grain weight was reduced from the ambient temperature regime by 8.7 to 14.5 per cent and number of grains per panicle was reduced by 30.6 to 46.7 per cent under elevated o temperature of 4.5 to 5.8 C from ambient. Similarly, the grain yield was reduced by 38.3 to 54.5 per cent o and biomass yield reduced by 19.7 to 33.6 per cent with increase under temperature 4.5 to 5.8 C from the ambient environment. Amongst the six cultivars the harvest index was maximum in cv PR-122 (33.0%), i.e., it is most tolerant to heat stress followed by PR-121 (28.3%) and least tolerant were cv PR-116 (20.2%) and PR-115 (18.9%). Keywords: Rice, stress, temperature gradient tunnel, plant height, tiller, yield  Rice is the most important food crop of the world and India is world's second biggest rice producer contributing 26% in world rice production. In tropical regions, it is cultivated as a summer crop despite relatively high temperatures that occur during its growth period (Sung et al., 2003; Bal et al., 2018) and heat stress is a common constraint during anthesis and grain-filling stages (Kobata and Uemuki, 2004). Global circulation models project that the global st average surface air temperature at the end of the 21 century o relative to 1980–1999 will be around 1.8–4.0 C, with a likely o range of 1.1–6.4 C (IPCC, 2007). Under high temperature induced atmospheric stress, the challenge to improve the rice productivity will be of an immense challenge for the farming community (Bal and Minhas, 2017). The rise in temperature affects the phenology, growth, yield, and quality of the rice crop (Sheehy et al., 2005). Yoshida (1981) revealed that within the temperature range of 22-31°C the growth rate of rice crop increases linearly and further increase in temperature adversely affect the growth and yield of rice. Studies have shown that under high temperature the rate of increase in plant height was steeper (Oh-e et al., 2007) and it increased with the rise of temperature within the range of 30-35 °C (Osada et al., 1973). The results of studies revealed that that in rice the tillering rate increases with rising temperature within the range of 15-33 °C, the optimum temperature during daytime is 25 °C and during night time is 20 °C (Sato, 1972) and further temperature above 33 °C were unfavourable for tillering (Chaudhary and Ghildyal, 1970). Yoshida (1981) revealed that the yield potential of a rice cultivar may be directly related to its capacity to produce tillers, however, more tillers in rice plant lead to more inconsistency in mobilizing assimilates and nutrients amongst the tillers resulting to more variability in development of grain within the tillers. An increase in temperatures may affect the mobilization / availability of photosynthates and nutrients amongst the tillers. Shouichi (1973) in a control experiment study observed that at early growth stages, growth rate is increased