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
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.
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.
Copyright 2014 The Nature