Romanian Biotechnological Letters Vol. 23, No. 1, 2018 Copyright © 2018 University of Bucharest Printed in Romania. All rights reserved ORIGINAL PAPER Romanian Biotechnological Letters, Vol. 23, No. 1, 2018 13264 Molecular characterization and identification of unique alleles for thermo-tolerance in wheat varieties Received for publication, June 15, 2016 Accepted, August, 11, 2016 PARDEEP KUMAR 1,2 , MEENU GOYAL 1,3 *, KHAZAN SINGH BOORA 1 , SANTOSH DHILLON 1 1 Department of Molecular Biology, Biotechnology and Bioinformatics, CCS Haryana Agricultural University, Hisar-125004, India 2 Division of Plant Quarantine, ICAR- National Bureau of Plant Genetic Resources, New Delhi- 110012, India 3* Department of Biotechnology, Central University of Haryana, Jant-Pali, Mahendergarh, Haryana-123029, India *Address correspondence to: Email: goyalmeenu333@gmail.com; Tel.: +91-9466747763 Abstract Genetic diversity of wheat cultivars is very important in reducing genetic vulnerability especially during high temperature stress. This study was conducted to estimate genetic diversity among wheat varieties and to identify the simple sequence repeats (SSR) markers linked to the high temperature stress tolerance in wheat. For this, wheat varieties already identified as thermo-tolerant and thermos- sensitive based on morpho-physiological parameters were characterized using SSR markers. Out of a total of 44 SSR markers used to study genetic diversity among 14 wheat varieties, 36 markers showed clear amplification pattern. The polymorphism percentage ranged from 33.3 to 100%, with an average value of 76.28%. The dendrogram prepared using NTSYSpc formed two major clusters at a similarity coefficient value of 0.68. At a similarity coefficient value of 0.751, all thermo-tolerant varieties clearly distinguished from thermo-sensitive ones. The microsatellite marker, Xgwm 46 amplified a 200 bp allele which was present in all the thermo-tolerant varieties but absent in all thermo-sensitive varieties. The identified SSR marker, Xgwm 46 was found to be thermo-tolerance specific and could be of potential use in wheat improvement programs through marker assisted selection. Keywords: Genetic diversity, SSR markers, Thermo-tolerance, Wheat 1. Introduction Wheat (Triticum aestivum L.) is the staple food to one third of the global population which makes it most important among field crops. It is cultivated under diverse environmental conditions varying from cool rain-fed to hot dry-land areas. In many areas of the world, high temperature stress is the major limiting factor for wheat production. The crop experiences varying degree of heat stress at different phenological stages, but reproductive phase is more sensitive to higher temperature than vegetative stage due to its direct effect on grain number and dry weight (B. WOLLENWEBER & al. [1]). The optimum temperature required for wheat anthesis and grain filling is from 12 to 22°C (H. TEWOLDE & al. [2]). Increase in temperature beyond optimum reduces the duration between anthesis and the physiological maturity, which is further associated with a reduction in grain weight (L. SHPILER & al. [3], B. LIU & al. [4]). Combined yield loss caused by heat stress is around 40 million tones for wheat, corn and barley per year, where wheat alone accounts for almost half of the yield loss (D.B. LOBELL & al. [5]). Global wheat production is estimated to fall by 6% for each degree Celsius of further increase in global temperature (S. ASSENG & al. [6]).