Journal of University of Duhok., Vol. 22, No.1 (Agri. and Vet. Sciences), Pp 193-203, 2102 https://doi.org/10.26682/avuod.2019.22.1.19 391 IMPACTS OF ELEVATED OZONE CONCENTRATION ON SOME PHYSIOLOGICAL AND MORPHOLOGICAL CHARACTERISTICS OF TWO WHEAT PLANT VARIETIES BAHZAD M.T. KHALED * and EZAT Y. RAOOF ** * Dept. of Horticulture, College of Agriculture University of Duhok, Kurdistan region- Iraq ** Dept. of Biology, College of Science, University of Duhok, Kurdistan Region –Iraq (Received: December 19, 2018; Accepted for Publication: February 23, 2019) ABSTRACT Tropospheric ozone is the most important atmospheric pollutant affecting agricultural crops due to its phytotoxicity. Wheat plant, as an important and dominant cereal crop has been found to be sensitive to elevated ozone levels leading to adverse effects on growth and productivity. The objective of this study is to assess the impact of the ambient air concentration and the future increase in tropospheric ozone concentration on some physiological and morphological traits of two wheat plant (Triticum durum) varieties, Semito and Creso. Open‐ top chamber (OTC) field experiments were conducted during two consecutive years 2016-2017 and 2017-2018 under environmental conditions of Kurdistan region of Iraq, accumulated exposure over threshold of 40 ppb (AOT40) was tested, the treatment were i) ambient air concentration (32- 37) ppb, ii) 50 ppb and iii) 60 ppb. Elevated Ozone concentration show a significant negative effect on total chlorophyll content (SPAD), relative water content, leaf area, plant height and consequently reducing above ground biomass, while in the same time induced increase in proline content in flag leaves. The present study demonstrate that the elevated tropospheric Ozone concentration significantly affect a range of important physiological and morphological characteristics of both varieties of wheat plant (T. durum). KEYWORDS: Tropospheric Ozone, Triticum durum, physiological traits, morphological traits INTRODUCTION ropospheric ozone (O 3 ) is recognized as one of the most effective regional and global atmospheric pollutant due to its phytotoxicity, causing threat to food security to feed the growing population across the globe (Sarkar et al, 2010). And acting as the most powerful greenhouse gases after CO2 and CH4, in opposite to stratospheric ozone which protect the earth biosphere living components from harmful ultraviolet radiation emitted from the sun (Solomon et al. 2007). Recently it’s identified as the most dominant countryside air pollutant, affecting vegetation, crops productivity and human health. As a result of huge anthropogenic emissions of O3 precursors e.g nitrogen oxide (NOx) and volatile organic compounds (VOC) during the last decade levels of tropospheric ozone has been increased in northern hemisphere by approximately five times from 10 ppb pre-industrial concentration to 50-60 ppb current concentration (Gauss et al. 2006). Approximately 25 % of earth surface is suffering from elevated ozone concentration to above 60 ppb particularly during summer time, when high light intensity and atmospheric pressure is prevailing, and this is above the standards of accumulated exposure over a threshold of 40 ppb (AOT40) which is crucial for injury to sensitive plant species (Monks et al., 2015). In addition the global climate change can force more pressure on tropospheric ozone emission e.g. by modifying emissions of ozone precursors particularly biogenic volatile organic compounds (e.g. isoprene) that may be very effective to climate change in the same time (Nakicenovic and Swart, R., 2000). In Asia mean monthly tropospheric O3 concentrations usually exceeding 50 ppb during crops growing season (Lu et al, 2010). And furthermore various simulating modeling projects indicate that globally might have more increase in ozone concentration throughout the 21 st , by 20– 25% between 2015 and 2050, and by 40–60% by T