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Insect-resistant, transgenic cotton was more susceptible to fungal disease than its parent line.

Manipulated Organism: (Gossypium hirsutum).

Inserted Transgenes: cry1A gene derived from Bacillus thuringiensis (Bt) and the CpTI gene from cowpeas, which produces a trypsin inhibitor. These proteins are toxic to various insect pests.

Goal of This Study: Motivated by reports from several Chinese provinces that GM insect-resistant cotton varieties had reduced disease resistance, the authors investigated the resistance of GM varieties and their respective non-GM parental lines to the soil fungus Fusarium oxysporum.

Results of This Study:
  • The GM cultivar Zhong-41 was derived from the cultivar Zhong-23, which is known for its resistance to F. oxysporum. However, Zhong-41 showed significantly more injury (wilted, yellow leaves) than Zhong-23 when exposed to F. oxysporum, with a disease index rating of 76 versus 42 (Z-41 versus Z-23).

  • Whereas the germination rate of F. oxysporum spores in the presence of root exudate from Zhong-41 (GM) was 79%, with root exudate from Zhong-23 (non-GM parent) the fungal spore germination rate was only 48%.

  • Chemical analysis revealed significant differences in the composition of root exudates from Zhong-41 and Zhong-23. The more susceptible GM cultivar Zhong-41 produced exudate with elevated levels of several amino acids. Additionally, whereas glucose was the only sugar detected in exudate from Zhong-23, in Zhong-41 exudate the authors detected large quantities of fructose and maltose, which can support fungal growth.

Source: Li, X., B. Liu, S. Heia, D. Liu et al. (2009). "The Effect of Root Exudates from Two Transgenic Insect-Resistant Cotton Lines on the Growth of Fusarium oxysporum," Transgenic Research vol. 18, pp. 757-67.

Author Affiliations: Nanjing Forestry University, China; Ministry of Environmental Protection of China; Genok Center for Biosafety, Norway; Chinese Academy of Agricultural Sciences.

Funding: Jiangsu Science Foundation; China's National Special Transgenic Project.

Product Status: Transgenic cotton containing the cry1A and CpTI genes has been developed by the Chinese Academy of Agricultural Sciences and is widely grown in China.

Copyright 2009 The Nature Institute.

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