17 Aug 2019

Christian Huyghe, Some clear answers on GM crops

Published in Farming
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The endless questions and information on the use, benefits or innocuousness of GM crops suffer, in the eyes the general public, from a vagueness that is decidedly counter-productive. Each debate on the question invariably boils down to the opposition of two contradictory arguments that by confirming the opinion of both those “for” and those «against”, leave the citizen – producer or consumer – in the same state of confusion. It is therefore to try to see more clearly through this mass of contradiction, that we interviewed a scientist whose opinions represent an authority: Christian Huyghe, Deputy Scientific Director for Agriculture at INRA, the French agricultural research body.

Christian-HuygheAgriculture Internationale - Does the development of biotechnologies applied to agriculture and stock-rearing still constitute the best way to feed the 9 billion human beings who - according to the UN - will inhabit the Earth in 2050?

Christian Huyghe - Biotechnologies represent a technological breakthrough in that they enable the development of a far greater range of variation in most of the characteristics that determine the agronomic and technological value of the crop varieties we grow. Biotechnologies should not be reduced simply to the production and use of GM crops. The implementation of marker-assisted selection and now genomic selection has been made possible thanks to better knowledge of genomes. The challenge of 2050 cannot be reduced solely to the obligation to feed 9 billion people. We have to meet this challenge whilst preserving the environment, both in terms of the extraction of resources and impact on habitat. Reducing the extraction of resources therefore presupposes that we make more efficient use of natural resources (water, hydrogen and phosphorous) and do not merely increase the volume produced per surface unit.

We must also be able to do this in conditions that are socially acceptable for producers, consumers and citizens alike. So it is not appropriate to reduce the question to a mere biotechnological equation: feeding 9 million inhabitants. We must look for a more overalll transition. Biotechnologies, via GM crops and doubtless even more so through the introduction of genomic selection will contribute to this, but the resulting varieties will have to be developed for, and exploited in, production systems that have been radically overhauled. We must therefore consider a thorough modification of our production systems based on a new paradigm, for example one founded on agro-ecological concepts that ensure sustainability and do not simply seek to maximise production per surface unit.

A.I. - What solutions does Research hold to the questions, worries even, raised by transgenesis applied to crops, notably in terms of a suitable alternative to the growing needs of industry and the world’s populations?

C.H. - Transgenesis is a technique. Its use must be mastered and deployed in conditions that are acceptable to all. In the field of transgenesis, the answer provided by research to the questions you mention consists of acquiring the expertise needed to inform public decisions on the choices available, their biological, agronomic, economic and environmental consequences and on the conditions under which it might be used. It also consists of exploring the potential offered by other means of obtaining genetically improved varieties and notably its acceleration through the use of marker-assisted selection.

The answer also lies in scale approaches to the production system overall where diversification plays a key role in ensuring sustainable production. At this level, the development of transgenesis and genomic selection represents a challenge since these technologies tend to develop over a limited number of species, which is contradictory to the need for diversification and which could generate blockages.

A.I. - Could the introduction of a gene with an insecticide or fungicide effect into a plant result over time in the soil in which the plant grows becoming sterile?

C.H. - Once again, we must not confuse the effect of the modified plant and the effect of the consequences on the cropping system. The plant as such will not result in the milieu in which it grows becoming sterile. However, if the introduction of a genetically modified variety is done at the same time as the production system changes, it could have indirect results. For example, the introduction of GM soya tolerant of a well-known systemic weed-killer into the Argentine Pampa was accompanied by radical modification of the production systems, with simplified rotation, the very frequent return of soya as a main or catch crop, mainly sown directly since resistance to the weed-killer meant that weeds could be controlled, at least in the short-term. However, in the long-term, these simplified systems are vulnerable: there is the risk of the emergence of parasites on the one hand, and on the other, the fertility of the soils is endangered. Hence, once again, the importance of taking the production system as a whole into consideration.

A.I. - Could the potential dissemination - natural or induced - of genetically modified plants represent a serious threat to biodiversity in the long-term?

C.H. - The dissemination of a transgene in a natural habitat brings pressure to bear on the wild populations of the same or related species, as does the use of new varieties resulting from traditional selection methods. Yet pressure does not mean threat for all that. Where pressure becomes threatening is when the dissemination of the transgene is accompanied by the application of a selection agent which will give this transgene a considerable selective advantage. So if a gene that is resistant to weed-killer spreads through the wild or traditional populations, the diversity of these populations will be in danger when a selective herbicide is used.

A.I. - Certain destructive insects are now resistant to the insecticide gene introduced in certain varieties of GM crops. Is it scientifically possible to prevent this type of mutation and if so, would it be economically viable?

C.H. - No, it is difficult to prevent a destructive insect mutating when it is subjected to the pressure of selection and this has been particularly well documented in the case of resistance to Bt genes. Measures that limit the appearance of such resistance must therefore be taken. Several mechanisms can be implemented but this must be done in a concerted fashion by all the players. The first option consists of using genes that have a strong effect and do not give the destructive insect any chance of accumulating alleles that allow it to adapt to the insecticide. Then, it is preferable to use resistance conferred by several genes rather than just one. This is also true when it is a question of resistance obtained by traditional selection.

The simultaneous use of monogenetic resistance and polygenetic resistance must also be avoided. Avoiding the first, which is easier, makes the use of the second virtually inoperable. However, this means solid concertation between all the players in a country or group of countries. Lastly, to slow down the genetic evolution of the population of destructive insects it is recommended that a fraction of the surface under cultivation is planted with sensitive varieties. This enables the population of destructive insects to multiply without the pressure of selection and therefore slows down the increase in the number of resistant genotypes within a population of destructive insects.

A.I. - Since plants resulting from mutagenesis are not subject to GM crop regulations, can this line of research be effectively adopted, that is to say, does it offer the same protection and production prospects, whilst at the same time reassuring users and consumers?

C.H. - Spontaneous mutagenesis is the main process that has generated the existing diversity within all species, animal and plant, cultivated or not. It is also at the origin of the diversity of the human race. Induced mutagenesis consists in increasing the frequency of the appearance of mutations. Targeted mutation consists in inducing a high rate of mutations in a particular area of the genome, even on a precise gene. But mutation does not provide exogenous genetic information. It is, moreover, often deleterious in rendering certain genes non-functional, which enables its functions to be studied. The absence of exogenous information significantly limits the risk of producing dangerous or risky substances. So induced, targeted mutagenesis is accompanied in the research laboratories by meticulous screening. A form of naivety exists that consists in believing that a few mutations can provide The Solution. Similarly, debates on regulations, mainly those concerning GM crops (only regulations on varieties and registering on the national and EU catalogue are compulsory for these varieties) and on the fact that it is a question of hidden GM crops, are rather sterile. The introduction of a mutation into a gene pool creates a new situation that is more or less favourable to quantitative progress.

ravageursIt should not be forgotten that the characteristics that determine agronomic and technological value are controlled by a large number of genes. Neither should we forget that it is the conditions of use and the cultural practices associated with these that will determine if the mutant that is planted is likely to produce a risk, or if on the other hand, the use of the variety that carries the mutation will give all the expected results. So the example of weed-killer tolerant varieties is interesting. In Europe today, we are seeing on the market a large number of resistant varieties of species, which are not native to that species. It is mainly a question of resistance to sulfonylurea drugs, conferred by a mutation of the target on the ALS (acetolactate synthase) gene. In the short-term, this option may appear seductive since it simplifies the practice of weeding with products that are fairly inexpensive.

It can also provide solutions for flora that have become resistant to previously used weed-killers and for which no other solutions exist. This is the case with thistles, ragweed and Datura on springtime species. But in the long-term, this option may prove dangerous. Indeed, sulfonylurea drugs are the most popular weed-killers for cereals and in particular the winter cereals that dominate the production systems of arable crops in Europe. The use of the same molecule on all crop rotations will severely weaken the solution that they provide today and may become a problem for crops as a whole. So it is the alternation of spring and winter crops, in other words a diversification approach that will slow down the selection of resistant weeds.

It is also the combined use of chemical weed-killers and mechanical weeding that will allow us to reduce the pressure of selection on adventitious flora and on the selection of resistant weeds. Finally, it is the alternation of ploughing and simplified cultivation techniques that will allow us to modify the seed bank and its place in the various crops we grow. More than ever before, we should be thinking in terms of the system, which engenders complexity. We may dream of simple solutions, but sadly, with plant production as with animal products, the options for multi-performance farming depend on complex initiatives that will require a greater understanding of the processes involved, and a different type of support for farmers to prevent complexity becoming a source of risk and generating rejection. We must also try to design resilient and consistent production systems and not only an increase in the average value.

* Deputy Scientific Director for Agriculture - INRA.

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