13 Journal of Wheat Research 7(1):13-17 Homepage: http://epubs.icar.org.in/ejournal/index.php/JWR Research Article Article history Received: 12 August, 2014 Revised : 30 January, 2015 Accepted: 03 February, 2015 Citation Puri RR, NR Gautam, AK Joshi. 2015. Exploring stress tolerance indices to identify terminal heat tolerance in spring wheat in Nepal. Journal of Wheat Research 7(1):13-17 *Corresponding author Email: rameshrajpuri@yahoo.com @ Society for Advancement of Wheat Research Exploring stress tolerance indices to identify terminal heat tolerance in spring wheat in Nepal Ramesh Raj Puri 1 *, Nutan Raj Gautam 1 , Arun Kumar Joshi 2, 3 1 National Wheat Research Program, Bhairahawa, Nepal 2 Department of Genetics and Plant Breeding, Indira Gandhi Agricultural University, Raipur, India 3 CIMMYT, South Asia Regional Ofice, Kathmandu, Nepal Abstract Terminal heat stress during anthesis and grain illing period accelerates maturity and signiicantly reduces grain size and weight. A study was performed to explore stress tolerance indices that can judge terminal heat tolerance in spring wheat in Nepal. Ten diverse lines were planted under normal (non-stress) and late (heat stress) sown condition at two locations (Parwanipur and Hardinath) in Nepal. The trial was set up in Alpha Lattice design with two replications in two consecutive crop cycles 2011-12 and 2012-13. Yield traits were recorded and stress susceptibility and tolerant indices were estimated. Correlation analysis showed that yield under stress environment had positive (r=0.80) and signiicant (p<0.05) association with that under non-stress environment. Similarly, grain yield under both environments had signiicant and positive correlation with mean productivity (MP), geometric mean productivity (GMP) and heat tolerance index (HTI) whereas non-signiicant correlation with stress susceptibility index (SSI) and tolerance index (TOL). The irst two principal components explained 97% of the variation. Biplot analysis revealed that stress tolerance indices can be used selection criteria for identiication of heat tolerant genotypes. Combined analysis showed that NL 1140 (SSI=0.71) possessed highest tolerance, followed by BL 3978 (SSI=0.79) while NL 1096 (SSI=1.5) appeared least tolerant. The most tolerant line NL 1140 produced mean yield of 3730.5 Kg/ha and 3000.3 Kg/ ha under normal and late sown condition, respectively. The HTI of this line was maximum (1.08) among the tested genotypes. NL 1140 and BL 3978 were identiied as promising for terminal heat tolerance and can be used directly as well as in the crossing program to heat tolerant genotypes of breed wheat. Keywords: Stress susceptibility index, Tolerance index 1. Introduction Temperature is a key environmental factor regulating both the rate of development and growth of crops (Slafer and Rawson, 1994), wheat being no exception. It has been projected that the increase in temperature will have a negative impact on crop production (Porter and Semenov, 2005). By the end of the 21st Century, the earth’s climate is predicted to be warmer by an average of 2-4 0 C (IPCC, 2007), due to both anthropogenic and natural factors (Eitzinger et al., 2010). This increase in temperature has exposed most of the world’s crops to heat stress during some stages of their life cycle. The dificulty in precise prediction of the projected agricultural impacts of climate change further adds to the uncertainty (Watanabe and Kume, 2009). Wheat (Triticum aestivum), a temperature sensitive crop, is presently being affected by terminal heat stress on a signiicant wheat growing area in South Asia with majority being in Eastern Gangetic Plains ( Joshi et al., 2007a). Globally, terminal heat stressed wheat is reported to be on 36 Mha area (40% of the temperate environment) (Hays et al., 2007). The current trends in Nepal, India and other neighboring countries indicate that the ‘cool period’ for wheat crop is shrinking, while the threat of terminal heat stress is increasing ( Joshi et al., 2007b).