Available online at www.scholarsresearchlibrary.com Scholars Research Library Annals of Biological Research, 2013, 4 (2):1-7 (http://scholarsresearchlibrary.com/archive.html) ISSN 0976-1233 CODEN (USA): ABRNBW 1 Scholars Research Library Influence of chemical stimulators in decreasing of allelopathic effect of Eucalyptus camaldulensis on germination properties of Onobrychis sativa Morteza Saberi 1 , Farajollah Tarnian 2 , Abolfazl Davari 1 , Ebrahim Shahreki 3 and Mojtaba Shahreki 3 1 Faculty of Natural Resources, University of Zabol, Iran 2 Faculty of Natural Resources, University of Tehran, Iran 3 Department of Agriculture, University of Zabol, Iran _____________________________________________________________________________________________ ABSTRACT This test was conducted on laboratory condition to investigate the allelopathic effect of Eucalyptus camaldulensis on germination and early seedling growth of Onobrychis sativa. Pretreatment with gibberellic acid and salicylic acid also was used to decrease the adverse effect of allelopathic components. Three levels of gibberellic acid (125, 250 and 500 ppm) and salicylic acid (100, 200 and 300 mg/L) and five extract levels of Eucalyptus camaldulensis (0, 25, 50, 75 and 100 %) was used in the test. This experiment was carried out as factorial experiment based on a randomized completely design with four replications. The results of ANOVA and compare mean test showed that Eucalyptus camaldulensis extract had inhibitive effect on germination and early seedling growth of Onobrychis sativa. Early seedling growth of Onobrychis sativa increased by pretreatment of seeds in chemical stimulators so that the highest effect was observed in gibberellic acid. Interaction effects of allelopathic and pretreatment with chemical stimulators were significance on germination percentage and speed, root, shoot and plant length and seed vigour index. Keywords: Allelopathy, Eucalyptus camaldulensis, germination, chemical stimulators, Onobrychis sativa _____________________________________________________________________________________________ INTRODUCTION Successful plant establishment, the most important step in determining the competitive ability and regeneration of range and crop plants, depends on germination potency and plant growth. Allelopathic compounds restrict plant growth through negative interactions with important physiological processes such as changing cell wall structure; prevent of cell division and activity of some enzymes. These compounds can also affect the equilibrium of plant hormones, absorption of nutrient elements, displacement of stomata, photosynthesis, respiration, protein synthesis, pigment, and changes in DNA and RNA structures [4]. Allelochemicals have inhibitory or stimulating effects on the growth, health, behavior, and biotic population of other organisms (plants, insects, microbes, etc.) [26]. Priming is used to improve germination, reduce germination time and embryo emergency, and improve establishment and performance of species [14, 17, 19]. Priming also applies to increase seed vigority and reduce losses from late plantation. Many researchers have reported that priming can increase germination percentage and emergence of weakened or damaged seeds [1].