Journal of Middle East Applied Science and Technology (JMEAST) ISSN (Online): 2305-0225 Issue 22(2), January 2014, pp. 91-95 91 The effects of Thrichoderma harzianom extract on the chlorophyll rate and nitrate concentration in two varieties of Lettuce in soilless culture system Sh. Ahooi 1 , H. Nemati 2 , H. Rouhani 3 , H. Aroiee 4 Abstract—In this study, the effect of extracts of TBi isolated strain of Trichoderma harzianum fungal species on increased or decreased amount of chlorophyll a and b as well as on the nitrate accumulation on lettuce in greenhouse conditions and in the soilless culture system was studied. The experiment was performed in a complete block randomized design with factorial arrangement of (2×4) in 6 replication. To conduct the research, four concentrations of 0%, 5%, 10% and 15% of the extract per each source, and also 2 varieties of Siahoo and Grade Lake were used. The amounts of chlorophyll "a" and "b" were measured by Lichtenthaler and Wellburn method; nitrate concentrations were measured using Spectrophotometer (Diazo) method. The test results showed that different levels of this fungus extract have had different effects on the parameters listed on lettuce plant. Among different levels used, the concentration of 5% included the highest concentration of nitrate and showed a significant difference at the 5% probability level with other levels. This level also had higher chlorophyll content than other levels, but the difference was not significant. The Siahoo variety showed higher nitrate accumulation as well as larger amounts of chlorophyll "a" and "b" compared to the Grade Lake variety, and the difference was significant at the 1% probability level. Keywords— Trichoderma harzianum, Soilless culture, Nitrate accumulation, Chlorophyll, Lettuce 1 Shahabuddin Ahooi, M.Sc. Student, Dept. of Horticultural Science, Ferdoowsi University of Mashhad, (corresponding author to provide phone: +989358712919; e-mail: shahabahooi@yahoo.com ). 2, 4 Hossein Nemati, Hossein Aroiee, Assistant Prof., Dept. of Horticultural Science, Ferdoowsi University of Mashhad. e-mail: nematish@yahoo.Com, aroiee@um.ac. ir 3 Hamid Rouhani, Professor, Dept. of Plant Protection, Ferdoowsi University of Mashhad. e-mail: hrouhani@yahoo.com I. INTRODUCTION ifferent types of microorganisms live in soil and this group includes pathogenic and nonpathogenic factors. Among the known microorganisms which are usually applied for protecting general health of the plant, Trichoderma fungal species are of high importance. Based on different researches, it seems that this fungus with food and spatial competitive power, sporulation in soil environment and particularly around root of most agricultural and nonagricultural plants and resistance induction in plant not only decreased pathogenic factors in soil but also promoted growth of shoot and root of some of these plants [5], [12], [10], [17], [6]. annual plant which has been transferred from coastal Europe or Central Asia to other parts of the world. Some of the researchers believe that India is the main source of lettuce [10]. Lettuce has Vitamins A, B, C and other substances such as iodine, iron, phosphor, magnesium, zinc, manganese and copper in terms of nutritional value. Today, lettuce is cultivated to extract oil from its corn and consume fresh fruit [3]. Lettuce is divided into two large groups: Lactuca sativa var capitata which has two types of Butter head and Crisphead and is produced almost in greenhouse conditions as hydroponic cultivation or soil greenhouse cultivations and Lactuca sativa var Crispa and Lactuca sativa var longifolia (which is known as Romain or Coshead) are cultivated in open space [4]. Lettuce is a leafy vegetable with a relatively high production and consumption in Iran and mostly is used in fresh consumption; thus, nitrate concentration rate in the product is of great concern. The nitrate amount is one of the most important factors in determining the quality of vegetables. Nitrate accumulation mostly occurred in the vessels, petioles and leaves can have undesirable impact on human health. Management of hydroponic systems, on the one hand, requires appropriate plant nitrogen nutriment to make achievement of high yield possible, and on the other hand, it should be tried to prevent the loss of the element, which may cause environmental pollution and the capital loss. One solution is the use of compounds capable of keeping the nutrients as reservoir and gradually providing them to the plant [10]. Today, due to excessive use of fertilizers containing nitrogen to D