Feb 18 2014

GM Potatoes and Disease Resistance

The issue of genetically modified food is an excellent one for skeptics – it is a complex question that mostly revolves around scientific data, popular beliefs are rife with myths, misconceptions, and ideology, there are active and well-funded campaigns of misinformation regarding GM, and it is a hugely important topic for society. The topic is too big to cover in one blog post, which is why I have been writing about it sporadically to cover different angles of this issue (see here, here, here, and here). I also was recently interviewed for Mother Jones, with the result in both article and podcast form. The comments after the article are especially revealing.

Much of the discussion around GMO involves the two most common GM traits, pesticide(Bt) production and herbicide resistance. While these traits can be very useful when used intelligently, the potential for GM technology is perhaps much greater in other realms, including disease resistance. Late blight alone, a disease that affects potatoes and tomatoes, is estimated to cost 3-5 billion dollars per year in the US, Europe, and developing countries, through the cost of fungicide use and crop loss.

A three year trial of a new GM potato variety has just concluded, demonstrating impressive resistance to late blight. The researchers took a gene (Rpi-vnt1.1) isolated from a wild relative of potato, Solanum venturii, and placed in into the potato variety known as Desiree. The results:

In 2012, the third year of the trial, all the non-GM potatoes became infected with late blight by August while the modified vegetables remained fully resistant to the end of the experiment.

Lead author, Jonathan Jones, makes several important points in the published paper. Our attempts to grow massive amounts of limited cultivars in order to feed the world will necessarily create selective pressures for pests and infecting organisms. Just as with antibiotics and bacteria, we are in an evolutionary arms race against these pathogens.

One weapon we have is chemicals, such as fungicides. These are necessary, but can result in resistance, are expensive, and do introduce large amounts of chemicals into the environment. Another approach is through improving the properties of the plants we grow to make them more resistant to their pathogens.

Traditional breeding methods are helpful, but, Jones points out, are too slow. It can take years to decades to cultivate a disease resistant variety through traditional methods, and by that time the pathogens have already evolved around the resistance. In other words, pathogens can evolve faster than we can cultivate resistance.

Direct genetic modification, however, is a much faster method of introducing disease resistance and gives us an edge against evolving pathogens. No one fix is ever going to be a final solution, and eventually pathogens will emerge that can get around anything we do to fight them. I will also point out that over-reliance on monoculture is a huge part of the problem. We need to increase the diversity in our crops as one strategy against pests and pathogens.

The new blight-resistant potatoes are a good demonstration of the role that genetic modification can play. The variety will result in decreased fungicide use and increased crop yield through reduced losses to blight. The authors report about the advantages of GM over breeding:

Previously, breeders were unable to prioritize Rpi genes that recognized the pathogen’s most indispensable effectors; now they can. Moreover, if one can combine multiple Rpi genes on one DNA construct (‘stacking’), then each gene can be expected to reduce the selection pressure against the other genes on the construct [21]. Furthermore, with genetically modified (GM) methods, one can insert the Rpi gene stack into a favoured variety and recover derivatives with all the properties of that favoured variety, but with the addition of blight resistance. By contrast, breeding not only breaks up favourable combinations of alleles in a variety of choice, but may introduce deleterious alleles of genes linked to the novel disease resistance, which are difficult to eliminate from subsequent breeding steps.

Critics, of course, have raised several concerns. The first is that the level of expression of the inserted genes may be lower than in the native plants. Low levels of pathogen resistance can increase the speed with which the pathogens will evolve to counteract the resistance. While this concern is legitimate, the stacking of multiple resistance genes will likely address this point.

The second issue is about safety. The transferred genes already exist in certain crops and so proponents argue that they are already known to be safe. Critics, however, argue that when the genes are transferred into a new species the results can be unpredictable and therefore they should be tested for safety.

Ironically, critics also argue that the new GM potatoes are not necessary because the resistance genes already exist in other non-GM potatoes. This ignores various benefits – getting the resistance genes into potato cultivars that have other desirable traits, and developing the technology to stack resistance rapidly in a way that stays ahead of evolving pathogens.

Perhaps the most telling critical response, however, was from Liz O’Neil, director of GM Freeze, quoted in this BBC article. 

“Is anyone really going to grow, sell or buy genetically modified potatoes? The law says that they will have to be labelled GM. Experience shows that the UK doesn’t want GM in its shopping basket, and British farmers are far too smart to grow something they can’t sell.”

So essentially the anti-GM lobby has done everything it can to stigmatize GM and require labelling so that the label and stigma can be used as a circular argument against GM.


These new GM potatoes, as with any GM product, are not a panacea or a perfect solution. It is a potentially very useful additional tool against a serious problem to modern agriculture.

It is also a pretty solid example of the best of GM technology. The genes come from a related species, they already are present in crops consumed by humans, they will result in reduced chemical use, improved profits for farmers, and reduced crop loss to blight (therefore more efficient land use, which is good for the environment). The potatoes are grown from tubers, and so there is no risk of cross-pollination or contamination.

In essence, all the usual anti-GM complaints do not apply to this particular GM crop. Opponents oppose it simply because it is GM.

Also, we have to look beyond this one crop to the larger issue of crop pathogens and our strategies for controlling them. I think Jones makes a very persuasive argument that GM technology is going to be essential in this fight, and we would be silly to deny our agricultural industry this potential tool. He expands further on his arguments here, pointing out that there are many crops threatened by pathogens (such as the Cavendish banana) and really our only hope of saving or replacing them is through genetic modification.

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