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Unintended Effects of Genetic Manipulation
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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.

This document: http://natureinstitute.org/nontarget/reports/cotton_007.php

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