Truth: GM crops do not increase yield potential – and in some cases decrease it

Myth at a glance GM has not increased the yield potential of crops. Though yield increases were seen in major crops in the twentieth century, these were due to improvements in conventional breeding, and not to GM traits. High yield is a complex genetic trait based on multiple gene functions and cannot be genetically engineered into a crop. Data comparing agricultural productivity for staple crops in the United States and Western Europe shows that Europe’s mostly non-GM production produces better yields with less pesticide than the US’s mostly GM production. Contrary to claims that Europe’s refusal to embrace GM is causing it to fall behind the US, the data show that the reverse is true: the US, with its mostly GM production, is falling behind Europe in terms of productivity and sustainability. The funding and research that are currently poured into GM crop research and development should be redirected toward approaches that are proven effective in improving crop yields, including conventional plant breeding as well as the use of agroecological practices. If GM cannot increase yields even in the US, where high-input, irrigated, heavily subsidized commodity farming is the norm, it is irresponsible to assume that it would improve yields in the Global South, where farmers may literally bet their farms and livelihoods on a crop.

GM crops are often claimed to give higher yields than naturally bred varieties. But the data do not support this claim. At best, GM crops have not performed consistently better than their non-GM counterparts, with GM soybeans giving lower yields in university-based trials.1,2

Controlled field trials comparing GM and non-GM soy production suggested that 50% of the drop in yield was due to the disruption in gene function caused by the GM transformation process.2 Similarly, field tests of Bt maize hybrids showed that they took longer to reach maturity and produced up to 12% lower yields than their non-GM counterparts.3 And trials of canola varieties in Australia conducted by the Grains Research and Development Council found that yields were 0.7 tonnes per hectare for GM and 0.8 tonnes per hectare for non-GM.4

In 2009, in an apparent attempt to counter criticisms of lower yields from its GM soy, Monsanto released its new generation of supposedly high-yielding GM soybeans, RR2 Yield®. RR2 Yield is an elite high-yielding soy variety with a new version of the GM Roundup tolerance gene inserted. But a study carried out in five US states involving 20 farm managers who planted RR2 soybeans in 2009 concluded that the new varieties “didn’t meet their [yield] expectations”.5 In June 2010 the state of West Virginia launched an investigation of Monsanto for false advertising claims that RR2 soybeans gave higher yields.6 This was part of a broader anti-trust investigation of Monsanto by the US Justice Department, which was, however, quietly closed in 2012 without reporting on its findings.7

A US Department of Agriculture (USDA) report of 2002 acknowledged the absence of yield gain from GM crops, stating, “GE [genetically engineered] crops available for commercial use do not increase the yield potential of a variety. In fact, yield may even decrease…. Perhaps the biggest issue raised by these results is how to explain the rapid adoption of GE crops when farm financial impacts appear to be mixed or even negative.”8

An updated USDA report in 2014 stated, “Over the first 15 years of commercial use, GE seeds have not been shown to increase yield potentials of the varieties. In fact, the yields of herbicide-tolerant [HT] or insect-resistant seeds may be occasionally lower than the yields of conventional varieties if the varieties used to carry the HT or Bt genes are not the highest yielding cultivars, as in the earlier years of adoption.”9

This should not surprise us. GM crops were not designed to increase yield: the vast majority of GM crops are engineered to tolerate herbicides and/or to contain an insecticide. The yield of a GM crop depends on the genetic background of the non-GM plants into which the GM traits are inserted. Yield is a complex trait that is the product of many genes working together. Much depends on the agronomic practices used, such as conserving and building soil fertility and structure. High yield cannot be conferred by the manipulation of one or a few genes, as occurs in genetic engineering.

Failure to yield

The definitive study to date on GM crops and yield is “Failure to yield”, by Dr Doug Gurian-Sherman, senior scientist at the Union of Concerned Scientists and former biotechnology adviser to the US Environmental Protection Agency. The study, based on peer-reviewed research and official USDA data, was the first to tease out the contribution of genetic engineering to yield performance from the gains made through conventional breeding.10 It is important to bear in mind when evaluating the yield performance of GM crops that GMO companies insert their proprietary GM genes into the best-performing conventionally bred varieties.

The study also differentiated between intrinsic and operational yield.10Intrinsic or potential yield is the highest yield that can be achieved when crops are grown under ideal conditions. In contrast, operational yield is obtained under field conditions, when environmental factors such as pests and stress result in yields that are less than ideal. Genes that improve operational yield reduce losses from such factors.

The study found that GM technology has not raised the intrinsic yield of any crop. The intrinsic yields of corn and soybeans rose during the twentieth century, but this was not as a result of GM traits, but due to improvements brought about through traditional breeding.10

The study found that GM soybeans did not increase operational yields, either. GM maize increased operational yields only slightly, mostly in years of heavy infestation with the European corn borer pest. GM Btmaize offered little or no advantage when infestation with European corn borer was low to moderate, even when compared with conventional maize that was not treated with insecticides.10

This interpretation is shared by the USDA report of 2014, which noted that while GM crops have not been shown to increase yield potential, “by protecting the plant from certain pests, GE crops can prevent yield losses to pests, allowing the plant to approach its yield potential.”9

“Failure to yield” concluded, “Commercial GE crops have made no inroads so far into raising the intrinsic or potential yield of any crop. By contrast, traditional breeding has been spectacularly successful in this regard; it can be solely credited with the intrinsic yield increases in the United States and other parts of the world that characterized the agriculture of the twentieth century.”10

“Commercial GE crops have made no inroads so far into raising the intrinsic or potential yield of any crop. By contrast, traditional breeding has been spectacularly successful in this regard; it can be solely credited with the intrinsic yield increases in the United States and other parts of the world that characterized the agriculture of the twentieth century.”

– Doug Gurian-Sherman, former biotech advisor to the US Environmental Protection Agency (EPA) and senior scientist at the Union of Concerned Scientists10 “Over the first 15 years of commercial use, GE seeds have not been shown to increase yield potentials of the varieties. In fact, the yields of herbicide-tolerant [HT] or insect-resistant seeds may be occasionally lower than the yields of conventional varieties if the varieties used to carry the HT or Bt genes are not the highest yielding cultivars, as in the earlier years of adoption.”

– US Department of Agriculture9

Non-GM farming produces higher yields with less pesticide

A peer-reviewed study led by researchers from the University of Canterbury, New Zealand, confirmed the conclusions of “Failure to yield”. The study analyzed data on agricultural productivity in the United States and Western Europe over the last 50 years, focusing on the staple crops of maize, canola, and wheat. It found that the US’s mostly GM production was lowering yields and increasing pesticide use compared to Western Europe’s mostly non-GM production.11

The yield reduction found in the US relative to Europe may be due in part to technology choices beyond GM plants themselves, because even non-GM wheat yield improvements in the US are poor in comparison to Europe. Therefore the mostly non-GM agricultural system of Western Europe shows more promise of meeting future food needs than does the GM-based US system.11

The study found that both herbicide and insecticide use is increasing in the US relative to Western Europe. Hence the agricultural system of Western Europe appears to be reducing chemical inputs and thus is becoming more sustainable than that of the US, without sacrificing yield gains.

Commenting on the finding, lead author Professor Jack Heinemann said, “The US and US industry have been crowing about the reduction in chemical insecticide use with the introduction of Bt [GM insecticidal] crops. And at face value, that’s true. They’ve gone to about 85% of the levels that they used in the pre-GE era. But what they don’t tell you is that France went down to 12% of its previous levels. France is the fourth biggest exporter of corn in the world, one of the biggest exporters of wheat, and it’s only 11% of the size of the US.

“So here is a major agroecosystem growing the same things as the US, corn and wheat, and it’s reduced chemical insecticide use to 12% of 1995 levels. This is what a modern agroecosystem can do. What the US has done is invented a way to use comparatively more insecticide… [US use] should be down to 12% too!”12

Heinemann was prompted to carry out the study by a claim from a British economics professor that Europe was falling behind the US in agricultural productivity because of its avoidance of GM. Heinemann and his team found that the data showed that completely the opposite is true: “Europe has learned to grow more food per hectare and use fewer chemicals in the process. The American choices in biotechnology [GM] are causing it to fall behind Europe in productivity and sustainability.”13

Conclusion

GM has not increased the yield potential of crops. Though yield increases were seen in major crops in the twentieth century, these are due to improvements from conventional breeding, and not to the introduction of GM traits. High yield is a complex genetic trait with multiple coordinated gene functions at its basis that cannot be genetically engineered into a crop.

Data comparing agricultural productivity in the United States and Western Europe shows that Europe’s mostly non-GM production produces better yields with less pesticide than the US’s mostly GM production. Contrary to claims that Europe’s refusal to embrace GM is causing it to fall behind the US, the data show that the reverse is true: the US, with its mostly GM production for staple crops, is falling behind Europe in terms of productivity and sustainability.

The funding and research that are currently poured into GM crop research and development should be redirected toward approaches that are proven effective in improving crop yields, including conventional plant breeding as well as the use of agroecological practices. These are by far the most efficient, affordable, and widely practised methods of improving yield.

If GM cannot increase yields even in the US, where high-input, irrigated, heavily subsidized commodity farming is the norm, it is irresponsible to assume that it would improve yields in the Global South, where farmers may literally bet their farms and livelihoods on a crop.

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