Bt maize varieties matured more slowly and had on average lower
grain yield and higher grain moisture content than conventional varieties.
Manipulated Organism:
Maize (Zea mays).
Inserted Transgenes:
crylAb gene from Bacillus thuringiensis (Bt). This gene
gives transgenic Bt maize (also called Bt corn) the ability
to produce insecticidal delta-endotoxin that can kill the larvae of the
European corn borer and other insect pests feeding on the corn. The gene
was fused to the cauliflower mosaic virus (CaMV-35S) promoter so that the
Bt gene would be expressed in all parts of the plant.
Goal of This Study:
Investigate whether there are any differences in yield or differential
responses to nitrogen fertilizer uptake between conventional commercial
hybrid maize varieties and Bt maize varieties. The researchers
carried out field experiments over three years and compared three to seven
different varieties of conventional hybrid maize with their near-isogenic
Bt maize counterparts.
Results of This Study:
-
"Some of the Bt hybrids took 2-3 additional days to reach silking
and maturity and produced a similar or up to 12% lower grain yields with
3-5% lower grain moisture at maturity, in comparison to their non-Bt
counterpart"(p. 199).
-
"In 2000, no Bt hybrids reached physiological maturity before the
killing frost while their corresponding non-Bt hybrids matured
or almost reached maturity" (p.204).
-
Bt plants were greener at harvest than their nontransgenic
counterparts, which may be connected with their late maturing and higher
moisture concentration at maturity.
The researchers conclude: "Our study showed that under the conditions
tested, Bt hybrids showed no higher yield potentials and thus added
no yield benefits over their near-isolines. . . . In Bt hybrids,
Bt gene or related cluster genes and promoters may have acted as
a negative impact on dry matter and/or grain yeild when ECB [European
corn borer] infestation pressure is low and/or corn crop encounters
drought or other environmental stresses. . . . Another potential negative
effect associated with the Bt hybrids is greater grain moisture
at harvest, which may increase the cost for drying" (p. 210).
Additional Comments:
Bt crops are designed with the goal to increase yields by reducing
pest damage. However, as this study notes, only a yield increase of about
4% would make up for the increase in costs associated with purchasing
Bt crops ($25-30 premium per hectare). Since this study
showed that under typical conditions of moderate corn borer infestation
Bt crop yield was in part similar to but usually less than in the
conventional counterpart, "where there is no severe infestation of ECB
[European corn borer], corn producers may not benefit from the use of
current Bt hybrids" (p. 210). They warn that "widespread use of
Bt hybrids in lower ECB [European corn borer] problem areas not
only increases the cost of production, but may also lead to negative
impact on non-target organisms in the environment" (p. 210).
Source:
Ma, B. L. and K. D. Subedi (2005). "Development, Yield, Grain Moisture,
and Nitrogen Uptake of Bt Corn Hybrids and Their Conventional
Near-Isolines," Field Crops Research vol. 93, pp. 199-211.
Author Affiliations:
Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food
Canada.
Funding:
Eastern Cereal and Oilseed Research Centre, Canada.
Product Status:
The varieties used in this study are commercially planted.
Copyright 2008 The Nature
Institute.
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