136 Present address: 1 Division of Genetics, ICAR-Indian Agricultural Research Institute, New Delhi; 2 Crop Improvement Division, ICAR-Indian Grassland and Fodder Research Institute, Jhansi. *Corresponding author e-mail: sharma.rk.rk@gmail.com. Indian Journal of Agricultural Sciences 91 (3): 468–73, March 2021/Article Selection parameters for improving grain yield of bread wheat under terminal heat stress VIJAY KAMAL MEENA 1 , R K SHARMA 1 *, SURESH YADAV 1 , NARESH KUMAR 1 , RAHUL GAJGHATE 2 and ATTAR SINGH 1 Division of Genetics, ICAR-Indian Agricultural Research Institute, New Delhi 110 012, India Received: 10 October 2020; Accepted: 05 November 2020 ABSTRACT Improving terminal heat tolerance is an issue of top priority in wheat breeding in the present era of climate change. Present study was carried out to identify the association among traits of economic importance under terminal heat stress environment. The grain yield/sq. meter under terminal heat stress environment recorded highly signifcant positive correlation both at genotypic and phenotypic level with grain weight/spike, number of spike/sq. meter, harvest index and 1000-grain weight in both the crop seasons. Path coeffcient analysis carried out using genotypic correlation coeffcients revealed that days to heading contributing maximum positive direct effect towards grain yield under terminal heat stress environment followed by grain flling duration. Other characters contributing positive direct effects towards grain yield were grain weight/spike, number of spike/sq. meter, harvest index and biological yield/sq. meter under both the crop season. Thus, for improving the wheat grain yield under terminal heat stresses conditions, breeder should aim for selecting genotypes with bold grains or high grain weight /spike, more number of tillers/sq. meter, higher harvest index and longer grain flling duration. Keywords: Bread Wheat, Correlation, Path Analysis, Terminal Heat Stress, Yield Components Bread wheat (Triticum aestivum L. em. Thell) is an important temperate cereal crop of crucial importance for national food security. The crop has been under cultivation in about 30 million hectares (14% of global area) to produce the all time highest output of 99.70 million tonnes of wheat (13.64% of world production) with a record average productivity of 3371 kg/ha (Mo A & FW, 2018).Wheat and barley are relatively well adapted to cooler environments and sensitive to increased temperature (Raza et al. 2019). Temperature is one of the main natural factors which played an important role in development of crop as different growth stages of a particular crop required a specifc or optimum range of temperature (Akter and Rafqul Islam 2017). Heat stress is a complex function of intensity (temperature in degrees), duration and rate of increase in temperature (Farooq et al. 2011, Hasanuzzaman et al. 2013). Wheat experiences heat stress to varying degrees at different growth stages, but heat stress or high temperature during the reproductive phase was found to be more harmful than during the vegetative phase due to the direct effect on grain number and dry weight (Fan et al. 2018).The optimum temperature for wheat anthesis and grain flling ranges from 12–22 0 C and rise in temperature above this range is harmful to grain yield. Therefore, improving the grain yield under terminal heat stress is of utmost priority. Unlike the biotic stress, heat stress is more complex in nature as it could not be measured on its own. It has to be measured in terms of its manifestation towards changing performance of a genotype for a given trait (Ram et al. 2015). To get the maximum grain yield under particular stress environment needs a specifc set of desirable characters in the crop plants. The association studies among the grain and yield component traits under terminal heat stress conditions led to identifcation of selection criteria to be used for selecting high yielding genotypes. Therefore, the present investigation was undertaken to examine the inter relationships among grain yield components and some physiological characters under terminal heat stress conditions. MATERIALS AND METHODS The experimental material for the present investigation is consisted of 36 diverse bread wheat genotypes including released varieties of different zones of the country and pre-released advance lines developed at wheat breeding programme of ICAR-IARI, New Delhi. These genotypes were sown at the Experimental Farm, Division of Genetics, https://doi.org/10.56093/ijas.v91i3.112536