March 2022 | Volume 35 | Issue 1 | Page 36 Pakistan Journal of Agricultural Research Research Article Introduction H eat stress as a result of high ambient tempera- ture is the one of the most alarming threat to crop production in Pakistan as well as Worldwide. It becomes more severe in spring crop during reproduc- tive stage i.e., anthesis and grain development stages when high ambient temperature coincides with these stages (Ghani et al., 2017; Yousaf et al., 2018; 2019; Riaz et al., 2021). Te normal temperature required for reproductive growth of maize crop ranges from 26°C to 31°C (Sánchez et al., 2014). Crop exposure to higher temperature (> 35°C) could signifcantly reduce maize kernel yield as reported by many re- searchers (Tornton et al., 2010; Lobell et al., 2011; Deryng et al., 2011; Ghani et al., 2020). Brown (2009) in a global study, reported a 10% reduction in kernel yield for every 1°C above normal temperature (29°C). It is also predicted that 8.1% reduction in kernel yield is expected in Pakistan by 2055 (Iqbal et al., 2011) due to clanging climatic conditions. Tese studies show that there is an utmost need for the selection Abstract | Te current study was conducted to evaluate maize hybrids for their high temperature tolerance ability based on their performance as assessed through diferent high temperature stress indices. Nine maize hybrids were screened under optimal and high temperature stress conditions (late sowing) for three consecutive spring seasons (Spring 2017-18, 2018-19 and 2019-20), laid out under split-split-plot design under RCBD. Results reveled signifcant diferences among stress indices for all three seasons and both conditions. Correlation analysis indicated that some high temperature stress indices i.e., STI, MP, GMP and HARM had a strong positive correlation with kernel yield under normal (Yp) and high temperature stress conditions (Ys). Biplot analysis further unveiled that two local maize hybrids i.e., YH- 5507 and YH-5427 were the most productive, stable and heat tolerant while YH-5532, P-1543 and NK-8711 showed poor performance under high temperature stress conditions as compared to normal sowing. High temperature stress indices could be efciently used to screen heat tolerant genotypes. Saleem Ur Rahman 1 , Muhammad Irfan Yousaf 1 *, Mozammil Hussain 2 , Khadim Hussain 1 , Shahid Hussain 1 , Muhammad Husnain Bhatti 1 , Dilbar Hussain 1 , Aamir Ghani 1 , Abdul Razaq 1 , Muhammad Akram 1 , Iqra Ibrar 1 , Muhammad Shakeel Ahmad 1 , Shoaib Anwar Kohli 3 , Muhammad Abubakar Siddiq 4 1 Maize and Millets Research Institute (MMRI), Yusafwala, Sahiwal, Pakistan; 2 Pakistan Agricultural Research Council, Pakistan; 3 Fodder Research Institute, Sargodha, Pakistan; 4 Soil and Water testing laboratory for research, Sargodha, Pakistan. Received | March 10, 2021; Accepted | October 12, 2021; Published | January 20,2022 *Correspondence | Muhammad Irfan Yousaf, Maize and Millets Research Institute (MMRI), Yusafwala, Sahiwal, Pakistan; Email: irfanpbg. uaf@gmail.com Citation | Rahman, S.U., M.I. Yousaf, M. Hussain, K. Hussain, S. Hussain, M.H. Bhatti, D. Hussain, A. Ghani, A. Razaq, M. Akram, I. Ibrar, M.S. Ahmad, S.A. Kohli, M.A. Siddiq. 2022. Evaluation of local and multinational maize hybrids for tolerance against high temperature using stress tolerance indices. Pakistan Journal of Agricultural Research, 35(1): 36-46. DOI | https://dx.doi.org/10.17582/journal.pjar/2022/35.1.36.46 Keywords | Climate change, Selection, Screening, Biplot analysis, Heat stress Evaluation of Local and Multinational Maize Hybrids for Tolerance Against High Temperature using Stress Tolerance Indices