Stop overselling GM on yield, warns plant breeding researcher

A young researcher studying plant breeding for her PhD at Cornell University has just published a paper warning GMO promoters not to make overhyped claims about supposed yield gains from GM crops. Merritt Khaipho-Burch is the first author on the new publication, called “Genetic modification can improve crop yields — but stop overselling it”.

Khaipho-Burch initially made her case on Twitter last year, comprehensively debunking papers published in Science Magazine reporting massive yield gains from genetic engineering in rice and soybean plants. The click-bait claims made by Science about these papers were lapped up uncritically by the mainstream media, leading Khaipho-Burch to condemn both papers as “misleading” and former Science Magazine reporter Michael Balter to accuse the journal of being “way too credulous” in certain topic areas of science, such as GMO research.

Now Khaipho-Burch and her co-authors have taken the discussion to a higher level, in the form of a peer-reviewed paper in the world’s leading multidisciplinary science journal, Nature, which drives home many points that GMWatch has been making for years. In this paper, Khaipho-Burch et al note that over the past two decades, journals have published papers describing how modifying one or a few genes with GM can result in substantial increases in crop yields, with reported increases ranging from 10% to 68%. But these are often the results of tests conducted in greenhouses or in small-scale field trials — the latter typically involving plants grown in small plots – and “hardly any findings have translated into yield increases on actual farms”.

Conventional breeding outperforms genetic engineering

Notably, Khaipho-Burch et al show that the real yield gains in major crops achieved in recent decades are the result of conventional breeding, not GM, combined with advanced agricultural practices, and that GM has made negligible improvements on those gains. As an example of the important role of farming practices, in maize, about 8.5–17% of the observed growth in yield can be attributed to a rise in planting density.

These vital points – which hitherto have been almost totally ignored in the pages of science journals – were raised as long ago as 2009 by US-based scientist Dr Doug Gurian-Sherman, in his report “Failure to yield”. The report, which GMWatch helped to publicise, concluded that conventional breeding and advances in agricultural practices have consistently outstripped GM in increasing crop yields. Commenting on his findings on breeding versus GM, Dr Gurian-Sherman said that when it comes to increasing yields, “Traditional breeding outperforms genetic engineering hands down.” 

We’ve only had to wait 14 years for his insight to be confirmed in the pages of a peer-reviewed journal!

Yield is a highly complex genetic trait

Khaipho-Burch et al also point out that yield is a highly complex, polygenic trait – in other words, one that is controlled by thousands of gene variants, with each one having a small effect. Manipulating one or a few genes with GM cannot produce significant yield rises. The genetically complex nature of yield traits is a factor that GMWatch has repeatedly drawn attention to over the years, for example, in a 2018 article by molecular geneticist Dr Michael Antoniou, in which he stated that only conventional breeding can maximise the full potential of the many genes affecting yield, by bringing together whole families of genes that act in networks.

Khaipho-Burch et al note that in spite of the hype generated around GM approaches (including gene editing) to increasing yields, conventional plant-breeding approaches used over decades paint a very different picture of what genetic modifications are likely to achieve in the coming decades. Breeders consider yield increases of 1–5% in a single plant generation as real breakthroughs – and “Although seemingly modest, these increases are actually remarkable in the context of total global production.” 

Khaipho-Burch et al caution that these increases must be validated in multi-year experiments in multiple locations around the world. A two-decades-long project of Corteva tested the effect of 1,671 genes from 47 species, on yield, nitrogen use, water use and other traits in maize. Only 1% of these genes (22 genes) increased yield enough in an initial trial to warrant more investigation. And in subsequent testing, only one gene (zmm28) generated the kind of yield improvements that the company had been hoping for.

The Corteva researchers used GM to introduce genetic changes that caused overexpression of this gene into elite (high performing) lines. Khaipho-Burch et al remind their readers that these elite lines have been obtained by conventional selective breeding – not GM – over the past 100 years. Corteva tested the resulting hybrids over 4 years in 58 locations. Khaipho-Burch et al comment: “All this field testing showed that the overexpression of zmm28 could increase the yield of maize by around 2%.” 

That figure, of course, is at the lower end of the range of the 1–5% yield increases that Khaipho-Burch et al indicate that breeders have achieved without GM in a single plant generation.

Soil and management regimes are crucial

Khaipho-Burch et al state: “Although single genes can affect yield, such genes always operate in conjunction with soil and fertilizer management regimes, the hundreds of other genes involved in crop domestication and adaptation, and so on.”

They further explain that crop yield has evolved under intense selection, “such that any gene variant that significantly increases yield across most of the environments and varieties of a crop in existence today has already been incorporated into breeding lines” through conventional breeding.

Given all this, Khaipho-Burch et al note that “it is unsurprising that none of the published studies claiming that a single gene or a few genes affect yield has been validated under conditions resembling those on farms”. But, they ask, “Why are such claims being published in the first place?” We couldn’t have put it better ourselves.

They suggest some possible answers: “Without plant breeders, quantitative geneticists or agronomists (researchers focused on soils and agricultural practices) in their teams, researchers might fail to ensure that yield assessments are conducted using appropriate experimental designs.” And “In high-impact, non-specialist journals such as Nature or Science, the problem might stem from editors not having enough contact with specialists in crop breeding and quantitative genetics — scholars who are trained to critically examine field-based experiments and yield trials.”

Five criteria that researchers and journal editors should check

Khaipho-Burch asks researchers, reviewers and journal editors to “ensure that at least five criteria are met whenever claims are made about the effects of single genes or a few genes on the yield of a crop”:
1) Studies should use standard definitions of yield, such as the weight of dry grain harvested per unit area, or the dry-matter content of the roots and tubers harvested per unit area, not some other metric such as grain length or width.
2) Trials should be replicated across plots, geographical locations and years. It seems that “In some cases, researchers record data from multiple plots in small-scale field studies but then report yields only from the best-performing plots or plants. More commonly, investigators measure yield in unreplicated trials, without considering variable environmental conditions (including future ones predicted by climate modelling), or the harvesting and other practices typical for that crop on real farms.”
3) Varieties, planting densities and other conditions, such as irrigation and fertiliser application, should closely match those on farms. 
4) Appropriate controls should be used. Measurements of yield in modified crops should be compared with the local or national yield of whatever crop is being investigated, not with some older variety that’s no longer used. The yields of older varieties can be 4–17 times less than for today’s commercial varieties. 
5) Researchers should prioritise genes that plant breeding might have missed: “Before investing considerable time and money in conducting research on a particular gene of interest, investigators should check that comparable alleles [gene variants] are not already present or fixed in commercial crop varieties. If plant breeders have already worked with a gene for decades, it is extremely unlikely that it will suddenly deliver major yield gains.”

The authors conclude their paper by advising researchers “to adopt tried-and-tested methods to accurately measure the impact of genetic changes on crop yields”.

We’d have thought that most, if not all, of these points were obvious to everyone capable of logical thought, but apparently not. The proof lies in the abundance of absurd claims of miraculous yield increases for GM crops published in otherwise respectable journals. As Kaipho-Burch et al note, “Few, if any [papers], have used the experimental designs needed to evaluate crop performance in real-world environments.”

GMO booster Pam Ronald joins voices of caution

From the moment Khaipho-Burch started laying out her arguments on Twitter, they were so convincing that even stalwart GMO booster Pam Ronald had to agree with her devastating takedown of the paper reporting 40% yield gains in GM rice. 

That was despite Ronald’s previous cheerleading for the very same GM rice paper in Science Magazine, where she was quoted in a news piece enthusing about the yield claim, “That’s a big number. Amazing.”

Now Ronald has even joined Khaipho-Burch as a co-author on the new paper debunking overhyped yield claims for GM. This is either a cynically opportunistic move on Ronald’s part (in terms of seeing which way the bandwagon is rolling and jumping aboard fast) or the start of her maturation into a more solidly evidence-based communicator on GM crops. Given Ronald’s record to date, there may be some understandable scepticism about the likelihood of the latter.

Dose of reality

All in all, Khaipho-Burch has done a service to scientists, journal editors, and policymakers around the world in bringing a dose of reality to the over-hyped world of GM crop research. Like the little boy in the fairy story of the emperor’s new clothes, she has dared to point out the delusion of GM super-yielding crops.


The new paper:
Khaipho-Burch M et al (2023). Genetic modification can improve crop yields — but stop overselling it. Nature 20 September 2023. https://www.nature.com/articles/d41586-023-02895-w#ref-CR5


Read this article on the GMWatch site and access linked sources:
https://gmwatch.org/en/106-news/latest-news/20291

__________________________________________________________