JJBS Volume 6, Number 2, June .2013 ISSN 1995-6673 Pages 151 - 230 Jordan Journal of Biological Sciences Response of Three Accessions of Jordanian Aegilops crassa Boiss. and Durum Wheat to Controlled Drought Amal M. Harb * and Jamil N. Lahham Department of Biological Sciences, Faculty of Science, Yarmouk Univeristy. Irbid, Jordan. Received: December 15, 2012; accepted: January 22, 2013 Abstract Drought is a major abiotic stress that is threatening the production and the survival of many crops such as cereals. The response of three Aegilops crassa accessions (C1, C2 and C3) that inhabit areas with different rates of rainfall and durum wheat to controlled drought (with soil moisture of 50% field capacity) was tested in terms of changes in: relative water content, chlorophyll content, chlorophyll fluorescence and biomass accumulation. At the end of drought treatment, a slightly significant decrease in relative water content (RWC) was shown in two Ae. crassa accessions (C2 and C3). RWC of C1 accession and durum wheat showed no change. In all Aegilops accessions and durum wheat, the effect of drought on chlorophyll content and chlorophyll fluorescence was minimal. A differential response to drought in terms of biomass accumulation was revealed. Ae. crassa C2 and C3 accessions that are adapted to semiarid and arid areas, respectively, showed no significant difference in their biomass under drought stress. The biomass of C1 accession that is adapted to well-watered area was significantly decreased. A highly significant decrease in biomass was also shown in durum wheat. Hence, C2 and C3 accessions of Ae. crassa are promising genetic sources for the genetic engineering of drought tolerant wheat plants. Future understanding the molecular basis of how drought-tolerant Aegilops species respond to drought stress, can be one of the approaches to improve drought tolerance in wheat. Keywords: Controlled drought, Ae. crassa, durum wheat, biomass, acclimation. * Corresponding author. e-mail: harbhope78@gmail.com. 1. Introduction Being sessile, plants are susceptible to environmental changes. Drought is a major abiotic stress, which challenge crop production and plant survival. Large body of information has been gained from studies of abiotic stress in the model plants Arabidopsis and rice at physiological, biochemical and molecular levels (Ingram and Bartels, 1996; Bartels and Sunkar, 2005; Shinozaki and Yamaguchi-Shinozaki, 2007; Nakashima et al., 2009). However, still a lot need to be learned about the complexity of plant interaction with the surrounding environment. Drought can be chronic in semiarid and arid areas with low water availability, or random and unpredictable due to weather changes during the growing season. Drought problem is exacerbating, due to global warming and climate change, in addition to the increasing demands of water for many purposes including agriculture. Therefore, studying the response of crop plants to drought will enhance our understanding of this problem. In addition, the screening of natural variations is a promising approach to harness traits that fit the changing environments (Nevo and Chen, 2010). Wild relatives of cultivated crops that are distributed in a wide climatic range are valuable genetic sources for the improvement of economic crop plants. Aegilops (goatgrass) belongs to Poaceae and is well known as the wild relative of wheat. Indeed, bread wheat (Triticum aestivum) resulted from the hybridization between wheat and Aegilops (Dvorak et al., 1998; Hedge et al., 2000; Faris et al., 2002; Petersen et al., 2006). Hence, Aegilops is considered as the progenitor of wheat. Twenty-three Aegilops species were identified (Kilian et al., 2011). Eleven species are diploids and 12 are allopolyploids. Aegilops plants exist with different types of genomes: A, B, D and G (Kimber and Feldman, 1987). Aegilops species are distributed in southwestern Asia. Aegilops is considered as a Mediterranean plant (Hegde et al., 2002). It was shown that Aegilops species inhabit warm areas with short winter and hot and dry summer (Baalbaki et al., 2006). Ae. crassa is distributed in different parts of Asia: Iran, Iraq, Afghanistan, Kazakhstan, Kyrgyzstan, Syria, Turkmenisatn, Usbekistan, Tajikistan, Turkey, Jordan and Lebanon (Kilian et al., 2011). Ae. crassa is considered