GM CROPS PART 3: What have GM crops done so far?

Other articles in this series:
Part 1: What are GM crops?
Part 2: Why do we need to improve our crops? What's wrong with the way they are now?

What have GM crops done so far?

Farmers have been growing GM crops since 1994 and they are now grown in 29 different countries. Most of the GM crops currently being grown are modified in one of three ways - they are either herbicide tolerant, insect resistant, or both. This article will explain what these things are and what they have achieved. I will then briefly introduce some of the other GM crops that have been grown.

If you like graphs and want to know more about the history and current status of GM crops around the world, I thoroughly recommend these slides.

Herbicide tolerant crops
When crops are grown in fields they have to compete with other plants (weeds) for the things that they need (water, soil nutrients, sunlight). This is a big problem for farmers because it means that the crops produce less food than they would if there were no weeds competing with them.

Farmers have a number of methods for dealing with weeds. Before the crop is planted, the field can be ploughed to destroy weeds. Once the crop is growing, the farmer can go into the field and remove weeds by hand. The general word used to describe mechanical methods such as these is 'tillage'. Another option is to spray the field with herbicides (chemicals that kill plants). Some herbicides are 'specific', meaning that they only kill certain types of plant, so the crop itself is unharmed.

However, all of these methods have their downsides. Tillage disturbs the soil, which causes greenhouse gasses to be released and results in soil being removed by the wind and rain. It is also time consuming and requires a lot of work. Herbicides pollute the environment, and the use of specific herbicides means that many different herbicides have to be used to make sure that all the different types of weed are killed. Also, herbicides are expensive, especially if you have to buy many different specific ones. As I mentioned in part II, many of the world's poorest farmers cannot afford herbicides.

Not all herbicides are specific. There are some that kill almost all types of plant. These are known as 'broad-spectrum' herbicides. Of course, the problem with using them is that they would also kill the crop. This is where GM comes in. Some plants and some bacteria have genes that tell them how to survive the broad-spectrum herbicides. These genes can be transferred to a crop, making it resistant to the herbicide. GM crops that have been created in this way are known as 'herbicide tolerant crops'. A farmer who grows herbicide-tolerant crops can spray their fields with broad-spectrum herbicides safe in the knowledge that the crop will be unharmed, while almost all weeds will be killed.

Farmers have been growing herbicide-tolerant crops for about 16 years now and it has had three main impacts:

Firstly, it has meant that weeds are killed more effectively. This means that more food is produced per unit of land and farmers no longer have to use mechanical methods such as ploughing which release greenhouse gasses and lead to soil degradation.

Secondly, it has caused farmers to switch from using many different specific herbicides to using just one of the broad-spectrum herbicides. Not only does this save the farmer money, it also benefits the environment because the commonly used broad-spectrum herbicides are less damaging to the environment than most specific ones.

Thirdly, the use of broad-spectrum herbicides means that less herbicide has to be used, because one spray of herbicide kills almost all of the weeds. Research shows that in the 12 years from 1996 to 2008, the use of HT crops caused a 5% reduction in the amount of herbicide used worldwide on cotton, soybean, maize and canola. This benefits the farmer because they spend less money on herbicide and less time spraying it, and the environment because less herbicide is released.

Insect resistant crops
Another problem that farmers face is insects eating their crops. One way to deal with this is to spray crops with insecticides (chemicals that kill insects).

However, there are a number of downsides to this approach. Many insects (such as the corn borer) are able to dig their way inside plants and lay their eggs there. Since insecticides are only sprayed onto the outside of the plant, the insects on the inside are not affected. Also, insecticides can be washed away by rain (which can lead to contamination of rivers). Also, although it is usually only one or two types of insects that are eating the crop, many insecticides are very general and kill lots of different types of insects (including natural enemies of the target insects). Insecticides are generally quite expensive and many of the world's poorest farmers cannot afford them. Poor farmers who can afford them often spray them onto the crops by hand. This means that the farmer comes into contact with a large amount of insecticide and poisonings are common in countries such as India and China.

There is a soil bacterium known as 'Bt' which has a special set of genes. Each of these genes tells it how to make one particular protein, and each of these proteins is poisonous to one specific type of insect. It is possible to take one (or more) of these genes and transfer it into a crop plant. This results in a 'Bt crop', which is able to produce its own insect poison. So far, Bt genes have mostly been used in cotton and maize and it has had many benefits.

Since the insect poison is constantly produced by the plant itself throughout the whole of the plant, there is no risk of it being washed away and it works inside the plant as well as outside. This means that the plant is better protected so more cotton is produced per field¹. Secondly, since each Bt protein is only poisonous to one particular type of insect, there is no harm to other insects² and there is no harm to the people who eat it or the farmers who grow it. Thirdly, there is no need for the farmer to buy or spray insecticide. This saves the farmer money³, prevents farmer poisonings⁴, and reduces the amount of insecticide released into the environment⁵.

What other GM crops are being grown?
Almost all of the GM crops that are currently being grown are plants that have been modified in one or both of the ways discussed above. However, there are a few other GM crops being grown in relatively small amounts. For a full list, see the slides I mentioned in the introduction, but here I will just mention one type that I think is quite interesting: the virus-resistant crops.

Just like animals, plants can be affected by viruses. It is possible to protect plants from viruses by transferring a harmless gene from the virus to the plant. This tells the plant how to produce a harmless protein that the virus usually produces. The plant's immune system then trains itself to recognise the protein, so that if it is attacked by the virus the plant will be able to recognise it quickly and destroy it. Papaya that has been modified in this way is grown in the USA and has been credited with saving the Hawaiian papaya industry.

PART 4: What could GM crops do in the future? (coming soon)
There are a lot of new GM crops that have been developed and are going to start being grown in the next few years. Most of these are very different to the ones currently being grown and often address different problems. Part 4 will introduce you to these new GM crops and what they could achieve.

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FIND OUT MORE ABOUT:
Herbicide-tolerant crops
Bt crops
The impacts that GM crops have had so far

REFERENCES:
1 Huang and co-workers, 2002 (table 3)^{↩(return to article)}

2 Lu and co-workers, 2012 analysed twenty years worth of data on the number of different types of insects in fields in northern China. They found that the introduction of Bt cotton over the last 16 years has led to a decrease in the number of aphids (which eat crops) and an increase in the number of spiders, ladybirds and lacewings (which eat aphids). They found that the presence of these aphid-eaters also protects nearby fields of non-GM cotton.^{↩(return to article)}

3 Huang and co-workers, 2002 (table 5)^{↩(return to article)}

4 Huang and co-workers, 2002 (table 6)^{↩(return to article)}

5 Huang and co-workers, 2002 (table 4)^{↩(return to article)}

Links

Hello to all my regular readers! Since you don't exist, you probably won't have noticed that I haven't posted here for quite some time. This is because I decided that I was going to 'take December off'. I realise now that this was a very poor decision because it meant that I started the new year with a list of articles that I wanted to read so long that it has taken me until mid-January to get through them (I use google reader).

The good news is that I am now back and have a big old stack of links for you. A few of them are things that I haven't actually read yet myself but since they look interesting and I don't want to leave the blog dormant for even longer while I get round to reading them, I have decided to just post them anyway. Enjoy!

• If you only follow one of these links, follow this one. It is a video of a talk given by the journalist and environmental activist Mark Lynas to the recent Oxford Farming Conference. In the talk, he apologises for the years that he spent campaigning against GM crops, says that he has now 'discovered science' and explains why he is now in favour of GM. Not only it is amazing that this has happened, it is also a really well-delivered talk, in which he explains his reasons very clearly. 

• Getting bacteria to produce useful chemicals for us is probably a much better idea than making them ourselves from oil. Mainly because it makes us less dependent on oil.

• Bread that lasts for 60 days could cut food waste. 

• A nice video from Kew Gardens about the Millenium Seed Bank Partnership. 

• 'Redrawing the Tree of Life' is a fantastic piece by Carl Zimmer about the way in which scientists have been rethinking evolution since the days of Darwin. 

• 'The GM crop risk-benefit debate: science and socio-economics' - this looks really good, but it is also quite long and I haven't gotten round to reading it yet. If you have read it, then let me know what you think. 

• Karl from the Biofortified Blog guides us through a recent talk he gave about the benefits and risks of genetically engineered crops.

• 'Counting the Cost of the Anti-GMO Movement' - argues that opponents of GM crops have actually done a lot of harm. 

• An interesting article about new food preservation techniques that are being developed.                (hat-tip to The Science of Food)

• 'GM crops increase biodiversity, study finds'. This is obviously very exciting news, but I think the headline should probably be more like 'one particular type of GM crop has been shown to increase biodiversity in one particular region of China'. If you're wondering how this is possible, the explanation is that this crop (BT cotton) requires less insecticide to protect it, so there is less damage to local insects. For more detail, see my post on BT crops or this 'BT cotton Q&A' document. 

• The cotton genome has been sequenced

Is Resistance Futile? How useful can GM really be in the battle to protect our crops?

Anyone who has studied military history will probably be familiar with the concept of an 'arms race'. One army develops some new type of weaponry which gives them the edge over their rival. The rival responds by developing a slightly better type of weaponry so that they now have a slight edge. This prompts a new development from the first army, which then prompts another new development from the second, and so on. As the process continues, both armies make a great deal of progress in terms of military technology, but very little progress in terms of their ability to overpower the other rival. They are both always either slightly stronger than, slightly weaker than or roughly the same strength as the other army.

Arms races are not just a human phenomenon, but are also a key part of evolution, including plant evolution. All plants are constantly locked into evolutionary arms races with two groups of living things: pathogens (organisms such as microbes and viruses that cause disease) and pests (organisms such as insects and grazing mammals that eat plants). As soon as a plant species evolves a new line of defence (a new poison perhaps), these pathogens and pests begin evolving some way of overcoming that defence (an antidote, for example). This arms race occurs not because the organisms want to outdo each other, but because of the inevitable pull of natural selection.

A cabbage plant which happens (not through design, but through sheer genetic luck) to be born with a new type of anti-slug poison will be more successful than the other cabbages around it and will produce more seed. Its offspring (which inherit the new line of defence) will similarly out-compete the cabbages around them. Within a few generations, the entire field will be full of slug-proof cabbages. It is only a matter of time, however, before a slug is born which (not through design, but through sheer genetic luck) is resistant to the poison. This fortunate creature will have access to all of the cabbage that the other slugs cannot eat and will therefore grow big and strong and produce lots of babies. Before long, all of the slugs in the field will be resistant to the poison. And so the arms race goes on. It is important to note the this slug only had an advantage because the poison existed. If the the poison did not exist then this slug would have had an antidote to a non-existent poison, which is no advantage. The existence of a defence actually causes the evolution of a counter-defence. It is a battle that has been raging for hundreds of millions of years and is not going to stop any time soon.

At some point, just a few thousand years ago, we got ourselves involved in this fight, and ever since we have been doing everything we can to protect our crops from pests and disease. Our most recent weapon is the use of genetic modification to give crops defence mechanisms that they might never have evolved naturally. For example, there are a group of genetically modified (GM) crops called the 'Bt crops' which have been given genes from a bacterium in order to protect them from insects that like to eat them.

The bacterium which donated the genes is a soil-dweller called Bacillus thuringiensis (Bt for short). Bt has a set of genes that allow it to produce a special group of anti-insect proteins. If an insect eat the bacterium, these proteins damage the inside of that insect's stomach, causing it to die. For decades, farmers (including organic farmers) have sprayed the bacterium onto their crops as a form of natural pesticide. Each of the anti-insect proteins affects only one type of insect, meaning that there is no harm to other organisms in the field, or to humans who eat the food.

There are two drawbacks to spraying crops with the bacterium. Firstly, it can be washed off by rain. Secondly it does not get inside plant stems, which is where some insects (such as the corn borer) like to lay their young. Transferring the Bt genes to crops solves these problems because it means that the plants themselves produce the proteins.

In the late 90s Bt cotton and Bt corn (which each contain one Bt gene for one Bt protein) were invented. They are now grown on hundreds of millions of acres around the world (mostly in the USA, Australia, China and India, but they are becoming more widespread in other countries; other Bt crops such as Bt rice are also in the pipeline). Not only has this raised yields, it has also reduced the use of pesticides, which can be harmful to the environment due to, among other things, their effects on non-target insects. In many countries, such as India and China, farmers previously sprayed powerful pesticides from containers on their backs, resulting in many farmers being poisoned. Since the introduction of Bt cotton the number of poisonings has gone down significantly.

But there is a problem with Bt crops, which you might be able to guess by now. At some point an insect might be born which is resistant to one of the Bt proteins. This would give it an advantage and before long there would be many resistant insects. Unfortunately, this has already happened, multiple times in multiple countries (including the USA, Pakistan and China). At the moment, resistant insects account for only few percent of the insect pests in those areas, but if nothing is done, it is only a matter of time before Bt-resistance spreads and Bt-crops become completely useless. But what can be done?

Well, ever since Bt crops were first grown, scientists have tried to prevent insects from becoming resistant by urging farmers to plant 'refuges' of non-Bt crops next to their Bt crops. This reduces the advantage that a Bt-resistant insect would have, since the other insects can still find some food. However, the advantage is only reduced, not completely eliminated, so while this strategy can delay the problem it cannot completely prevent it.

So is it hopeless to expect GM to protect our crops in a sustainable way? Well, actually, it might not be.There is a new technique called 'engineering durable resistance' that might just put an end to the arms race. It is a very simple idea and it works like this: rather than giving a GM crop one way to kill a pest or pathogen, you give give it multiple ways to kill that one pest or pathogen. For example, a new version of Bt cotton has been released in the US and Australia, which has two different Bt proteins that both kill the cotton bollworm. Now, a cotton bollworm which is born with resistance to one of the proteins has absolutely no advantage, because the cotton plant will still kill it. In order to have an advantage a bollworm would have to be born with resistance to both proteins, which is very unlikely. If the number of proteins was increased to say, 4 or 5, then the chances of a bollworm being born with resistance to all of them are vanishingly small.

Of course, it is impossible to know for certain whether this represents a long-term victory. In theory, durable resistance should provide lasting protection, but theory doesn't always turn out to be right. The appropriate response at this stage is probably something along the lines of quiet optimism.