Category: Genetic diversity

Graham Brookes and Bruce Chassy wrote a detailed rebuttal of a paper by G.F. Botta et al. in the American Journal of Plant Science, which questioned the value of GMO soybeans in Argentina. On the basis of their analysis, Brookes and Chassy conclude that:

The major deficiencies identified in this paper lead us to question the thoroughness of the review process undertaken by the American Journal of Plant Sciences, as it is our professional assessment that this paper should not have been accepted for publication in any reputable peer review journal.

I cannot dispute that. I can, however, point out that in seeking to orchestrate an invincible attack, Brookes and Chassy are perhaps guilty of stressing a single, not very helpful view of the nature of diversity, which is also entirely unnecessary to discredit the Botta et al. paper.

The main thrust of their rebuttal is to challenge the statements surrounding the use of the weedkiller glyphosate, and as an outsider that convinced me that the original paper was indeed deeply flawed. The two experts then go on to address another claim in the original paper.

‘Up until not recently agrarian diversity had always been increasing. However, in industrialized countries, plant and animal genetic engineers, trading houses and governments themselves combined forces to supply new varieties and uniform breeds that would replace the tremendous heterogeneity already existing’. ((Let’s leave aside entirely the very strange wording of this paragraph from Botta et al., and indeed the very title of their paper, despite the obvious clues they contain as to the worth of the journal they chose as the happy recipient of their research.))

That’s easy enough to skewer, and Brookes and Chassy do so well enough.

From the very beginning of agriculture biodiversity of crops has, in fact, been continually contracting as farmers and breeders selected the most desirable crops (see for example, L.T. Evans. Feeding the 10 Billion, Cambridge University Press).

Sloppy to confuse crops and varieties, but hardly criminal. Unfortunately, from my perspective, instead of leaving it at that, they go on to help readers to do something that they say Botta et al. have not done, viz.

to comprehend the nature of breeding modern crop varieties. While a single or limited number of varieties may be grown in one region at a particular time, this does not mean biodiversity is being lost. Quite the contrary, since modern varieties have complex combinations of parents this results in the incorporation of numerous diverse traits from many ancestors.

Yes. And, what is your point?

This argument deliberately or ignorantly confuses the differences among genetic diversity in a pedigree, genetic diversity within a population, and genetic diversity among populations planted at a given time in a given place. Brookes and Chassy then go on to show how crop failures that the rest of us associate with “reductions in ‘genetic variety’” are in fact no such thing. Forget their view of the Irish potato famine. Consider instead their account of Southern Corn Leaf blight, which halved maize yields in the US in 1970. Here is how Brooks and Chassy describe the cause of the epidemic:

In 1970, all US corn had, what is known as N cytoplasm (a designation of the genotype of the mitochondria).  Around this time a second cytoplasm called T was introduced which facilitated male sterility for hybrid seed production.  Ironically, it was the new cytoplasm that was susceptible to blight.

So far, so true. As a result of the widespread adoption of Texas cytoplasm to confer male sterility – because it makes the production of F1 hybrids easier and cheaper – almost all the maize planted in the US shared a single type of mitochondrial genome that rendered them all susceptible to Southern Corn Leaf blight. As far as that susceptibility is concerned, there was genetic uniformity in the crop, no genetic diversity at all. So how do Brookes and Chassy describe that?

So, in this case, it was an increase in diversity—not a decrease—that caused the problem.

How can they possibly say that?

Before the widespread adoption of Texas cytoplasm, there was a range of genetically-based susceptibilities among maize varieties. Afterwards, all varieties were susceptible. Because they all shared one set of genes.

Here is how a panel of the US National Academy of Sciences described what happened:

The corn crop fell victim to the epidemic because of a quirk in the technology that had redesigned the corn plants of America until, in one sense, they had become as alike as identical twins. Whatever made one plant susceptible made them all susceptible.
Uniformity is the key word–the plants were uniform in that special sense, and uniformity in a crop is an essential prerequisite to genetic vulnerability.

There are other aspects of the Brookes and Chassy rebuttal that I am unhappy with ((Ex-situ conservation is “much more effective at preserving biodiversity”. Why “farmers all over the world are willing to buy improved seeds”.)) but I’m sufficiently self aware not to pursue them here.

Instead, I’ll just conclude that genetic diversity in a pedigree is not the same as genetic diversity in a population, a species, or an ecosystem. Especially not as far as resilience is concerned.

Just the facts, ma’am
Friends will, I know, be wondering why on earth I’m bothering. Indeed, after a little digging, I wondered why Brookes and Chassy bothered too. The American Journal of Plant Sciences is published by Scientific Research Publishing, which has been described as a scam and which “borrowed” papers published elsewhere and called them its own. It may be peer-reviewed, in the strict sense, but it is also clearly a joke. So why bother debunking a joke? Equally, Academics Review, the site where Brookes and Chassy (who is one of the founders) published their debunk, seems to be withering on the vine. The debunk itself isn’t dated, although on 20 March David Tribe (another founder of the site) gave notice that Chassy and Barfoot have just put out a dissection of Botta et al. ((I’ve no idea who this Barfoot cove might be.)) Few of the pages at Tribe and Chassy’s site seem to have a date, and there hasn’t been any “news” since May 2010. It’s all a bit sad, because a repository of countervailing facts would be useful, especially if not sullied by internal errors.