Drought resistant crops would have huge benefits, particularly in the many areas of the world where lack of water limits yield. Selective breeding is yet to produce fully drought-resistant plants, so it is no surprise that people have looked to GM to speed up the process of developing drought-resistant plants.
Earlier this year, David Lawlor from Rothamsted Research published a review paper about drought resistance, having studied books on GM crops and peer-reviewed literature. Based on this evidence, he concluded that GM plants may currently not be better able to cope with drought than other varieties. Genetic modification for drought resistance has been very promising in laboratory conditions, but Lawlor writes that GM varieties have not yet produced ‘clear evidence of substantial improvements in crops under drought in the field’.
He found a large number of studies which claimed to have achieved drought resistance, with many different alterations to the plants genomes. These mechanisms were little understood – how had the plants’ physiology changed? What characteristics were actually leading to better performance in low water conditions – a root system better able to extract water, a change to the plants’ metabolism?
The limits to our understanding of plant biology perhaps means that genetic modification is not as precise and targeted as we like to believe.
What he did find was that studies in the laboratory and in limited field trials often showed that GM plants took longer to show signs of stress after they stopped being watered. This appeared to be because of decreased water loss from GM plants, often due to changed structure of the leaves. A change to the metabolism has not been demonstrated, but hypothetically could produce ‘drought tolerance’ rather than just a delayed onset of stress. This is a key point – we haven’t fundamentally changed a plant’s metabolism to make it properly drought resistant, just allowed it to retain more water (or potentially absorb more from the soil).
Perhaps in the field this delayed onset of stress will increase yields on the farm (at least in some conditions), and so we could argue that this means our current genetic modification technology for drought resistance has been a success. Field trials do, however, have the potential to show a downside of the modifications – changed leaf structure could theoretically lead to reduced yields when there isn’t a drought.
No doubt many people will disagree with Lawlor’s conclusions, but it does tie in with what I found during the neonicotinoid debate. I saw little evidence of what was actually occurring in the field, even though there were lots of claims about the effects of pesticides both on yields and on bees. Laboratory studies are essential, but what is really important is what is actually happening on the farm.
Lawlor DW (2013). Genetic engineering to improve plant performance under drought: physiological evaluation of achievements, limitations, and possibilities. Journal of experimental botany, 64 (1), 83-108 PMID: 23162116
An interesting aside from Lawlor’s review was that the number of papers produced per year about genetic modification for drought resistance suddenly started to increase rapidly in 2002.