[Frontiers in Bioscience, Landmark, 18, 725-733, January 1, 2013] 725 Root exudates of transgenic cotton and their effects on Fusarium oxysporum Xiao-gang Li 1, 2, 3 , Qin Wei 2 , Biao Liu 2, * , Mohammad-Saiful Alam 4 , Xing-xiang Wang 1 , Wenjing Shen 2 , Zheng-min Han 3 1 China Key Laboratory of Soil Environment and Pollution Remediation Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China, 2 Nanjing Institute of Environmental Sciences, Ministry of Environmental Protection of China, Nanjing 210042, China, 3 College of Forest Resources and Environment, Nanjing Forestry University, Nanjing 210037, China, 4 State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China TABLE OF CONTENTS 1. Abstract 2. Introduction 3. Materials and methods 3.1. The cotton lines and the pathogen 3.2. The collection and treatment of cotton root exudates 3.3. The effect of cotton root exudates on the spores germination of F. oxysporum 3.4. The effect of root exudates on the mycelial growth of F. oxysporum 3.5. The resistance of cotton to F. oxysporum 3.6. GC-MS analysis of root exudates 3.7. Statistical analyses 4. Results 4.1. The resistance of different cotton lines to cotton F. oxysporum 4.2. The effects of cotton root exudates on the growth of cotton F. oxysporum 4.3. The chemical composition of the root exudates from transgenic insect-resistant cotton and their parental cotton lines 4.4. Compare of the chemical composition of the root exudates in the transgenic insect-resistant cotton and their parental cotton lines 5. Discussion 6. Acknowledgements 7. References 1. ABSTRACT The components of the root exudates from two transgenic insect-resistant cotton lines and their parental cotton lines, and their effects on the growth of Fusarium oxysporum were investigated. The results demonstrated that the resistance of transgenic insect-resistant cotton to F. oxysporum was significantly reduced compared with their parental lines. Likewise, the root exudates from transgenic insect-resistant cotton significantly promoted the spore germination and mycelial growth of cotton F. oxysporum. The types of compounds found in the root exudates of transgenic insect-resistant cotton were similar to those of the parental cotton, but the composition and relative content of the compounds were different. The type and content of the fatty acids and esters were significantly reduced in the root exudates of the transgenic insect- resistant cotton, as were certain specific materials, whereas several alkanes were increased. The inhibition of the soil- borne pathogen F. oxysporum caused by the root exudates from the transgenic insect-resistant cotton was decreased compared with the parental cotton. This result provides a scientific basis for the decline in disease resistance in transgenic insect-resistant cotton. 2. INTRODUCTION Cotton is an economically important crop in China. Cotton Fusarium wilt, a vascular disease caused by the soil-borne F. oxysporum f. sp. vasinfectum, affects the stable yield of cotton all over the world and is a major constraint on cotton production in China (1, 2). Transgenic insect-resistant cotton expressing the Cry1Ac and/or CpTI protein was first released in China in 1997 and was able to effectively control the cotton bollworm (Helicoverpa armigera), thus protecting the environment by reducing the application of chemical insecticides and conferring great socioeconomic benefits (3). At present, transgenic insect- resistant cotton represents more than 70% of the total cotton grown in China (4). However, transgenic proteins, such as Cry1Ab, can be released into the soil by means of root exudates and cotton residuals during the course of its growth and after harvest (5-9), which can cause environmental risks, such as adverse effects on soil microorganisms and soil invertebrates (10-15). In biosafety assessments, the ecological risk of foreign proteins expressed by transgenic plants has attracted more attention in the scientific community (16-20) than the unpredictable changes caused by the compulsory insertion of exogenous