5081 Journal of Applied Sciences Research, 8(10): 5081-5088, 2012 ISSN 1819-544X This is a refereed journal and all articles are professionally screened and reviewed ORIGINAL ARTICLES Corresponding Author: Ebtihal, M. AbdElhamid, Botany Department,Agricultural and Biological Research Division, National Research Centre, Cairo, Egypt. E-mail: dr.ebtihal1777@yahoo.com Performance Of Flax Cultivars In Response To Exogenous application Of Salicylic Acid under Salinity Stress Ebtihal, M. Abd El-Hamid and Mervat Sh Sadak Botany Department, Agricultural andBiological Research Division, National Research Centre, Cairo, Egypt. ABSTRACT Salicylic acid (SA) is an important signal molecule modulating plant responses to stress. Recently,it has been reported that it induces multiple stress tolerance in plants including salinity.Adverse effects of salinity (3000 and 6000 mg/l) on growth, some physiological responses and yield quantity and quality of two cultivars (Sakha 2 and Amon) of flax (Linum usitatissimum L.) plant were studied. Salt stress induced reduction in growth (length in cm, fresh and dry weight / plant in g of shoot and root) and indole acetic acid (IAA) content.While increased total phenol contents of plants of the two cultivars at 75 days old. Also, yield and yield components (technical and total shoot length in cm, and dry weight of shoot / plants in g) and fibre yield (fibre length (cm), fibre weight /plant (g), fibre % and straw yield /plant in g) were decreased except fibre % of Amon cultivar increased, as compared with those of control plants. In addition, cellulose % and cellulose/lignin % were decreased significantly meanwhile lignin % increased when compared with those of control plants. Foliar application of salicylic acid (SA) at 200 and 400 mg/l counteracted the adverse effect of salinity, this accompanied generally by significant increases in plant growth, IAA & phenol contents and yield components. Moreover, foliar treatment of salicylic acid(SA) resulted mostly in an increase in fibre yield when compared with those of the control plants and the corresponding salinity levels. In addition, cellulose% and cellulose/lignin% were increased significantly over control and the corresponding salinity levels plants meanwhile decreased lignin%. Key words: - Flax, salt stress, salicylic acid, IAA, phenol, cellulose lignin and fibre. Introduction Flax (Linum usitatissimum) plant has been grown in many different countries as linen fibre, linen seed and double purpose plant (seeds for oil and shoots for fibre) in the same time. It is grown in Egypt as dual purpose crop. Flax is the second fibre crop after cotton in our country with regard to the cultivated area and economic importance. Now it could be considered as a versatile crop, however flax fibre can be exploited to produce many different products, it is the raw materials of textile, twines and different kinds of paper especially bank note. For its importance it is considered an important crop in our economic policy through its local fabrications as well as exportation (El Harriri, et al., 1998).The cultivated area through the last 20 years was decreased from 60.000 to 30.000 feddan due to the great competition of other economic winter crops resulting in a gap between production and consumption. Therefore, it is necessary to increase flax productivity per unit area which could be achieved by using high yielding cultivars (Ibrahim, 2009) and use some compounds such as antioxidants. In Egypt, the large scale land reclamation requires enormous amounts of water for irrigation in order to ensure vigorous plant growth and high yield. This has made it necessary to use various sources of irrigation water, which often have relatively high salinity levels such as well water. Salt stress is considered one of the most important abiotic stress limiting plant growth and productivity (Sairam and Tyagi, 2004), through the increase in reactive oxygen species (ROS) which may cause oxidative stress resulting in cellular damage by oxidation of lipids, proteins and nucleic acids (Beltagi, 2008).To minimize the effect of oxidative salt stress, plant cells have evolved a complex antioxidant system which is composed of low molecular mass antioxidants as well as ROS-scavenging enzymes (Apel and Hirt, 2004). One approach for inducing oxidative stress tolerance would be to increase the cellular levels of antioxidants such as salicylic acid. Salicylic acid (SA) has been considered as a signal molecule that may promote the generation of reactive oxygen species during salt stress thus play an important role in stress tolerance (Horvath et al., 2007a). Salicylic acid (SA) acts as a potential non-enzymatic antioxidant as well as a plant growth regulator, which plays an important role in regulating a number of plant physiological processes. Some earlier reports show that exogenous SA could ameliorate the damaging effects of salt stress (Arfan et al., 2007). These observations suggest that SA being an oxidant could be linked to oxidative stress. Several developmental, physiological and biochemical functions of