Morphological And Physiological Response of Two Accessions of Citrullus colocynthis to Drought Stress Induced by Polyethylene Glycol. Zahra Mohammadzade and Forouzandeh Soltani *

A biotic stresses can directly or indirectly affect the physiological status of an organism by altering its metabolism, growth, and development. In order to study the effect of drought stress on Citrullus colocynthis samples a factorial experiment was conducted in Horticultural science Department of University of Tehran in 2013. The first factor was two accessions of Citrullus colocynthis (Yazd and Khorasgan) and the second factor was water deficit induced by different osmotic potential levels 0 (the control), -0.4 MPa (slight), -0.8 MPa (moderate) and -1.2 MPa (severe (using polyethylene glycol.  The results indicated that fresh and dry weight of seedlings and leaf area decreased in both accessions as osmotic potential increased. Khorasgan samples showed higher net photosynthetic rate than Yazd accession in all osmotic condition. Total phenolic content, antioxidant capacity and proline content of leaves varied between two accessions which Yazd accession represented higher value at different osmotic condition. The present data suggest a relation between proline and total phenolic content and water stress also well-developed antioxidant defense mechanism activated during water stress .Based on this study Yazd accession was more tolerant to drought stress and could use in breeding or grafting program to improve Citrullus species growth under water deficit condition.