International Journal of Agriculture and Crop Sciences. Available online at www.ijagcs.com IJACS/2013/5-7/756-760 ISSN 2227-670X ©2013 IJACS Journal Morphological response of German chamomile to heat stress accompanies salicylic acid-mediated under field conditions Mojtaba Ghasemi 1 , Nadali Babaeian Jelodar 1 , Mohammad Modarresi 2* , Nadali Bagheri 1 1. Department of Plant Breeding and Biotechnology, Faculty of Crop Science, Sari Agricultural Sciences and Natural Resources University, Sari, IRAN 2. Department of Plant Breeding, College of Agriculture and Natural Resources, Persian Gulf University, Bushehr, IRAN Corresponding auther email: Modarresi@pgu.ac.ir ABSTRACT: In order to the study effect of salicylic acid on morphological characters of German chamomile (Matricaria chamomila L. cv Bona) under heat stress conditions. Field experiment was carried out as completely randomized block design with 3 replications. Treatments of this experiment including one German chamomile cultivar (Bona) and five levels of salicylic acid (0, 1, 10, 25 and 100 mg.L -1 ) were applied. The seeds were sowed in the heat stress sites. Late planting date was set that more growth stages and full flowering period, faced with high temperature. The morphological traits included plant height, capitol diameter, flower wet weight and flower dry weights were assessed. Analysis of variance showed that salicylic acid levels had significant effect on all growth parameters. According to our result, salicylic acid caused increasing heat tolerance of German chamomile under field conditions. At the end of this work, we suggested salicylic acid 100mg.L -1 treatment as the best treatment under heat stress in field conditions. Key word: German chamomile, Heat stress, Salicylic acid, Morphological traits INTRODUCTION Chamomile (Matricaria chamomilla L.) is important among existing medicinal plants and is cultivated throughout the world to obtain the essential oil from the flower heads. It is native to Europe and northern and western Asia, has been naturalized in Australia and North America, and is extensively cultivated in Hungary, Romania, Bulgaria, the former Yugoslavia, Germany, Greece, Argentina and Egypt (Nidagundi and Hegde, 2006). Heat stress due to increased temperature is a crucial problem in many areas in the world. Transitory or constantly high temperatures cause an array of morpho-anatomical, physiological and biochemical changes in plants, which affect plant growth and development and may lead to a drastic reduction in economic yield (Wahid et al. 2007). Heat stress affects plant growth throughout its ontogeny, though heat-threshold level varies considerably at different developmental stages. For instance, during seed germination, high temperature may slow down or totally inhibit germination, depending on plant species and the intensity of the stress (Wahid et al. 2007). At later stages, high temperature may adversely affect photosynthesis, respiration, water relations and membrane stability, and also modulate levels of hormones and primary and secondary metabolites (Wahid et al. 2007). In plants, salicylic acid (SA) is a signaling molecule regulating disease resistance responses such as systemic acquired resistance (SAR) and the hypersensitive response (HR), and has been implicated in both basal and acquired thermotolerance. It has been shown that SA enhances heat-induced Hsp/Hsc70 accumulation in plants (Snyman et al, 2008). Heat tolerance can be induced in a plant by prior exposure to moderately high temperatures which enables the plant to cope with subsequent, potentially lethal, heat exposure (Howarth and Ougham, 1993). This acclimatization is termed thermotolerance. SA has been found to be involved in both basal and acquired thermotolerance in plants (Dat et al., 1998a, b, 2000; Lopez-Delgado et al., 1998; Larkindale and Knight, 2002). SA also has the ability to enhance the heat shock response (HSR) by potentiating the heat-induced levels of the heat shock protein 70