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Unintended Effects of Genetic Manipulation
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Posted: October 2014

Yield Differences Between Insect-Resistant Bt Rice and Non-GM Rice

Rice is the world’s most important food crop and increasingly genetically modified (GM) varieties of rice are being developed and planted commercially. As the authors of a study by Chinese scientists remark, “the insertion of external genes into rice genomes usually causes phenotypic variations, such as reduced grain filling percentage, reduced plant height, shorter root length and fewer grains per panicle” (Wang et al. 2012). These researchers worked with two different lines of insect resistant Bt rice, one of which (MH63(2A*)) produced ten times more of the insecticidal protein than did the other (MH63(1C*)). They compared the yield of these two lines with that of the non-GM parent variety (MH63). All plants were grown under field conditions that were kept free of weeds and animal pests, including the insects that the Bt crops are meant to protect against.

Grain yields in the GM line MH63(1C*) were consistently and significantly lower than in the other GM line and in the non-GM parent variety. The latter two had varying yields depending on the year and site, but on the whole yields were not significantly different. Wang et al. write that “agronomic and physiological analysis revealed that poor grain filling percentage was the main reason for the yield reduction.” This poor filling of the grains occurred despite the fact that overall biomass, leaf area, nitrogen accumulation, and numbers of flowers in the plants was similar to that of the non-GM parental line and other GM line. They did find, however, that there was a lower content of growth-promoting phytohormones in the flowers, which may have inhibited the grain filling. How the lower production of these phytohormones was connected to the genetic manipulation is not at all clear.

It was also unexpected and surprising that the line that produced less Bt toxin—i.e. the line in which the targeted effect was less pronounced—was also the one that yielded less.

Source:
Wang, F., C. Ye, L. Zhu et al. (2012). “Yield Difference Between Bt Transgenic Rice Lines and the Non-Bt Counterparts, and Its Possible Mechanism,” Field Crops Research vol. 126, pp. 8-15. doi:10.1016/j.fcr.2011.09.017

Copyright 2014 The Nature Institute.

This document: http://natureinstitute.org/nontarget/reports/rice_006.php

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