103 Indian Journal of Agricultural Sciences 91 (3): 435–9, March 2021/Article Changes in thermal requirements, growth and yield of wheat under the elevated temperature B CHAKRABARTI 1 *, A BHATIA 1 , P PRAMANIK 1 , S D SINGH 1 , R S JATAV 1 , NAMITA DAS SAHA 1 , A RAJ 1 , R JOSHI 1 and V KUMAR 1 ICAR- Indian Agricultural Research Institute, New Delhi 110 012, India Received: 24 September 2020; Accepted: 27 October 2020 ABSTRACT A field experiment was conducted inside a temperature gradient tunnel (TGT) at the ICAR-Indian Agricultural Research Institute, New Delhi during rabi 2014–15 to quantify the impacts of elevated temperature on thermal requirement, growth and yield of wheat crop. Wheat crop was subjected to five temperature treatments, i.e. +0ºC (representing ambient condition), +0.9ºC, +2.5ºC, +2.8ºC and +3.5ºC.Temperature elevation of 3.5°C increased accumulated growing degree days (GDD) and photo-thermal unit (PTU), thereby hastening maturity of the crop. Leaf area index (LAI) of the crop was affected most by the high temperature at the anthesis stage. Temperature elevation by 2.5°C and above significantly reduced the LAI of wheat. Grain weight decreased by 17.1%, while the straw weight reduced by 10.5% with temperature elevation of 3.5°C. Temperature elevation by 2.5°C and above significantly reduced the straw weight, but grain weight of wheat got significantly reduced even with 0.9°C elevated temperature. Reduced number of spikes per/m 2 and number of grains/spike decreased grain yield. In fact, the increase in the spikelet sterility contributed towards the grain yield reduction. The information generated from this study will help in developing the appropriate management practices for production of wheat crop. Keywords: Elevated temperature, LAI, Thermal requirement, Wheat yield. 1 ICAR-Indian Agricultural Research Institute, New Delhi. *Corresponding author e-mail: bidisha2@yahoo.com. According to the recent fifth assessment report (2014) of the Inter-Governmental Panel on Climate Change (IPCC) based on the different representative concentration pathways (RCPs), it has been reiterated that the warming of the atmospheric system is unequivocal. Global climate has experienced a warming of about 0.85°C over the period of 1880 to 2012 (IPCC 2014). Agriculture sector being very sensitive to changes in the climate is expected to get immediately affected by any change in the climatic parameters as well. Wheat (Triticum aestivum L.) is the second major food grain crop grown in India and occupied 31.19 million hectares area with a production of 95.85 million tonnes during 2013–14 (Bishnoi and Hooda 2018). It is highly climate-sensitive and its growth and developmental stages are affected by temperature (Dubey et al. 2019). Temperature directly and indirectly affects the different growth parameters by influencing the water supply, substrate availability and the soil microbial activity. Several studies have reported that a crop plant completes its life cycle faster, under elevated temperature condition (Nahar et al. 2010, Challinor and Wheeler 2008). There are reports that elevated temperature reduced the photosynthesis rate, leaf area as well as grain weight in wheat (Shah and Paulsen 2003). Increase in maximum and minimum temperature throughout the cropping season might change the thermal requirement of the crops. Hence it is important to quantify the effect of elevated temperature on the changes in thermal requirement, growth and yield of major crops like, wheat as it would have crucial implications on the global food security. In our earlier investigation, the photosynthesis rate, stomatal conductance and root growth of wheat was observed to be reduced at higher temperatures (Pramanik et al. 2018). However, studies on the effect of increasing temperatures on changes in thermal requirement of wheat and their relationship with the crop phenology, growth and yield are still very limited. Hence, the present study aimed to quantify the changes in thermal requirement of wheat and their relationship with growth and yield under the elevated temperature conditions. MATERIALS AND METHODS Experimental details: The study was carried out at the Genetics H farm site of the ICAR-Indian Agricultural Research Institute (IARI), New Delhi, India during rabi (November to April) 2014–15. The site is situated at 28°35'N and 77°12'E having subtropical and semi-arid climate. The experiment was carried out inside the temperature gradient tunnel (TGT) in an area of 15 m × 2.5 m soil surface. The https://doi.org/10.56093/ijas.v91i3.112527