Why Biotech Should Be Employed For Crop Disease Resistance

Glassy-Winged Sharpshooter - Vector of Pierce's Disease of Grapes

Most of the “GMO Crops” that have been commercialized are either insect resistant or herbicide tolerant.  Biotechnology can also be used to generate crops that are resistant to plant diseases.  So far, there are only two examples of disease resistance available to farmers: the papayas resistant to ringspot virus and squash resistant to zucchini yellow mosaic and watermelon mosaic viruses.  That narrow offering is not for a lack of need or technical potential.  In fact, biotech approaches could uniquely address some of the most significant disease issues in global agriculture.  The limitation mainly reflects the success of the anti-GMO movement in creating controversy.  This has induced brand-sensitive food system players to use their leverage to prevent the development or introduction of “GMO” disease resistant versions of crops where they would make the most sense.

If we let ourselves imagine what could be, there are three important categories of plant disease of particular interest for the use of genetic engineering:

1. Systemic diseases spread by insect vectors
2. Diseases of crops for which conventional breeding is far too slow and/or disruptive to key quality attributes
3. Crop diseases which are not amenable to safe and effective chemical control

 Systemic diseases spread by insect vectors

Fungi cause most plant diseases, but plants can also be infected by viruses and bacteria.  In most of these cases, specific insects spread the pathogens from plant to plant in much the same way that the Aedes aegypti mosquito spreads a human disease like Yellow Fever.  For plants, the vector insects are the ones that use specialized mouthparts to penetrate plant cells to suck out nutrients – things like aphids, thrips, mealy bugs and psyllids.  The viruses or bacteria have specific associations that allow them to be picked up from an infected plant on the mouthparts of the “bug” and then released inside of the next plant.  Those infections can severely damage the plant and even kill it.  In many cases, the only way such diseases can be controlled is to use insecticides to kill the vectors.  Often it requires nearly complete insect control to adequately protect the crop.  That means intensive insecticide use in some cases, but in other cases it isn’t feasible to stop the spread of the disease.  That was the case with papaya ringspot virus which was seriously compromising production Hawaii in the early 1990s - the farmers were fighting a losing battle to save their plantings.  The introduction of transgenic virus resistance in 1998 saved the papaya industry.  Currently there is a new, deadly, bacterial disease of citrus which is threatening the orange industry in Florida.  Insecticide programs have only slowed the progress of the disease, and without something like a transgenic solution, that industry will soon collapse.  Another bacterium is threatening the California wine industry because of the introduction of a more problematic vector in the late 1980s.  Insecticide programs and quarantine programs are limiting the issue to Southern California for now, but it would be much more desirable to have a resistance option to deploy to protect the key production areas to the North.  Laurel Wilt disease of avocado is another similar challenge.

Diseases of crops for which conventional breeding is far too slow and/or disruptive to key quality attributes

One of the main ways that plant diseases are managed is through conventional breeding programs.  This can be quite effective, particularly for annual grains or vegetables for which breeding programs can progress fairly quickly.  For a crop like potatoes, breeding is difficult and slow because the plants don’t normally make any seeds.  That is why the 100+ year-old Russett Burbank is still a major commercial cultivar. There is a severe disease called Potato Late Blight which caused the infamous Potato Famine and which requires very frequent fungicide applications today.  There are genes for resistance in wild or semi-wild ancestral potatoes in the Andes, and using biotechnology, such genes have been moved into the potatoes we now grow, at least on an experimental basis.  This trait involves a potato gene in a potato.

Coffee also has a major rust disease that is causing increasing problems in the high quality, “Arabica” coffee production areas of Central and South America.  There are resistance genes in various other coffee species around the world, but to move those traits into high quality lines requires things like chromosome doubling and decades of back-crossing.  If the genes were moved via genetic engineering methods, the end result would be a coffee-based resistance gene in a coffee variety with a well-characterized quality background.

Bananas are an extreme case where genetic engineering would allow moving a resistance trait from some non-commercial, seeded banana, into the seedless banana of commerce which is threatened by Panama Wilt and other diseases. Similarly, genetic engineering may be a way to deal with something like Frosty Pod in cacao without compromising quality attributes.

Even with a crop like wheat, there are so many different types for different uses around the world that it would be helpful to speed up the breeding process for the new, UG99 Wheat Stem Rust threat, which is moving around the world.  A desirable gene found in one category of wheat (e.g. Hard Red Spring) could be moved to elite breeding lines for other types like Durum or Soft White Winter.

Diseases that are not amenable to safe, effective chemical control

There are many crop/disease combinations that can be effectively controlled using fungicide treatments with low mammalian toxicity and low environmental impact.  However, there are some diseases that are not amenable to that sort of control.  A disease of tomatoes, called Bacterial Leaf Spot, is a big issue in wetter growing regions like Florida.  It is currently managed with a combination of biological agents and copper-based products, but coppers are not as safe as most modern pesticides.  Foliar bacterial diseases do not comprise a large enough global market to justify the investment of >$200MM that it takes to develop a new synthetic pesticide.  There is a very effective resistance gene for this disease in peppers, but although they are related to tomatoes they are too distant for conventional cross-breeding.  That pepper gene has been moved to tomato and the plants performed well in field tests.   Fusarium Head Blight of wheat is a serious disease risk that limits the feasibility of adding wheat to Midwestern corn/soy rotations.  That disease is difficult to control with fungicides, but there was once a nearly commercialized trait for resistance.  

There are a number of crops including field corn that can be infected by the opportunistic fungal pathogen, Aspergillus flavus, when there has been drought stress and/or insect damage.  Fungicides are not very effective against this problem, and the aflatoxin that the fungus can produce renders the grain unsuitable for normal feed or food uses.  Indeed, aflatoxin is one of the leading causes of death in the developing world where it can contaminate important food crops like maize or peanuts.  There are several ideas for how to address that issue with biotechnology.

Biotech crops have been planted on hundreds of millions of acres of land each year since 1996.  Many generations of animals have been raised on these crops both in the countries where “GMO” crops are grown, and also in the EU, Japan, China and many other importing regions.  The arguments against this basic technology have not proven to be of actual concern.  At some point, we should be able to start applying these well-tested technologies to the prevention of problematic diseases that affect crops. 

Glassy-Winged Sharpshooter image from California Department of Food and Agriculture

Biotech potato image from Jonathan Jones Lab at Sainsbury Laboratory

Corn infected by Aspergillus image from Iowa State University

You are welcome to comment here and/or to email me at savage.sd@gmail.com.  I may not be answering comments quickly as I'm on vacation in Colorado :)

Do GMO Crops Foster Monoculture?

Do GMO crops "foster monoculture?" This is a frequent criticism of modern agriculture. I have three with problems it:

1. "Monoculture" isn't the right term to use to describe the relevant issues - its really about a limited crop rotation
2. History and economics are the drivers behind this phenomenon, not crop biotechnology
3. The solutions - to the extent that they are needed - are not what most critics seem to imagine

The Corn Belt of the Midwestern US, is a multi-million acre farming region almost entirely dominated by just two crops - corn and soybeans.  This phenomenon is often termed "monoculture,"  but monoculture is merely the practical approach of growing a single crop in a given field.  The opposite of monoculture is "polyculture" and it is entirely impractical for even minimally mechanized farming.

The Corn Belt is more accurately described as an example of a "limited crop rotation." The typical pattern is an alternation between corn and soybeans in each field.  There are also some fields where the growers plant continuous corn or continuous soybeans. There are many reasons that a more "diverse crop rotation" could be a good idea.  Mixing up crop types over time can help build soil quality because of different rooting patterns or residue characteristics. Some plant pests can be more easily managed if their life cycles are disrupted by cropping changes.  All of this is well known, but for a variety of reasons that I'll discuss below, the less diverse rotation persists.  

Corn and soybeans happen to be crops which involve widespread use of biotech crop options, but there are many other farming areas with a narrow crop rotation where "GMO" options have never been available. There are areas in Northern Europe where "continuous wheat" is the norm and many premium wine regions where essentially only grapes are grown. If farmers somewhere are not using a diverse crop rotation - there is a rational explanation involving history, economics, and risk management.

The Heart of the Corn Belt

Let's start by looking at Iowa, which sits in the very heart of the "Corn Belt." As you can see from the graph to the left, corn has been the dominant Iowa crop for a very long time, because Iowa is just about the ideal place to grow that crop.  Most farmland in that part of the Midwest is "rain-fed" rather than irrigated. The amount of rain that typically falls in Iowa is sufficient to produce a good corn crop without limiting yield by the number of cloudy days.

The rainfall in Central Iowa is usually "just right" for corn

The growing season is long enough and warm enough, but usually does not involve the yield-limiting heat that is typical further south.  Corn is heavily planted because it typically returns the highest net profit with the least risk.  The income potential from corn is what drives the cost of land for purchase or rent. As the farming population shrank and farm size increased over the last century, the remaining growers have expanded somewhat through land purchases, and more commonly through rentals.  For a farmer to keep up with a mortgage or lease typically requires growing a lot of corn.

Back in the 1930s, the main crop that was rotated with corn was oats - ironically much of that to be used as a "transportation biofuel" for horses.  Starting in the 1940s, soybeans began to evolve into the favored rotational crop - mostly as an animal feed with a co-product of oil for human consumption. Soybeans have much lower yield than corn, but they are able to generate their own nitrogen fertilizer (with microbial help) and don't require many other inputs. Thus, soy has also been a reliable way to generate enough profit to cover land and operating costs. All other crops have only ever had niche status in Iowa. When biotech crops arrived they were simply sold into that pre-existing market.

Illinois and Indiana have also been mostly two crop states ever since soybeans filled in for declining oat demand in the 50s and 60s.  There has alway been a small, but significant wheat sector in both of these states, part of a "double cropping" system in which corn is followed by winter wheat and then soy, producing three cash crop harvests in two years.  Indiana now has a small alfalfa segment - a case of crop diversification "fostered by a GMO crop."

The Northern Edge of the Corn Belt - Minnesota and North Dakota

Minnesota had a more diverse agriculture than its neighbors to the south, but like them, it replaced oats with soybeans long before the biotech era. The expansion of soybeans has continued in the biotech era, partially because of the attractiveness of Roundup Ready Soy, but also because cultivars better adapted to colder springs have also been introduced through conventional breeding. Barley, rye and flax have declined in the biotech era as has wheat to some degree.





The recent decline of wheat is even more pronounced in North Dakota as it went from approximately 50% of all plantings to about 30%. As in Minnesota, the rapid increase in soybeans came from a combination of  more cold tolerant lines and the herbicide tolerance trait. Corn plant-ings have also increased in the biotech era. For both crops the expansion is mostly in the wetter Red River Valley portion of the state.   The expansion of corn and soy at the expense of cereals like wheat, barley and rye may seem like a case where biotech is reducing rotational diversity, but the story is a bit more complex.

There is a disease of wheat and barley called Fusarium Head Blight, which has been an increasing issue in all five of these states since the 1980s (and again in 2014).  Corn, and particularly the crop residue in no-till corn, serves as a source of spores which can then infect the wheat or barley during their bloom period.  Head blight is difficult to control and it can lead to significant yield losses.  Infection can also lead to contamination of the grain with a mycotoxin called DON- or more colorfully, "vomitoxin."  Throughout the Midwest, wheat does not tend to have as much profit potential as corn or soy even in good years, but the risk of severe yield or quality loss from Head Blight is really what makes wheat much less attractive.  Biotech had the potential to help wheat keep a place in the Corn Belt rotation, but that solution was thwarted by anti-GMO campaigning.

Fusarium infected wheat (right)

There was a "GMO wheat" in advanced development around 2002 which was much more resistant to Fusarium Head Scab. This product had the potential to reduce the risk of growing wheat, both in the historic wheat growing states like ND and MN, but also in the "I States." Unfortunately, the trait was never commercialized. Major wheat importing companies in Europe and Japan put pressure on the US and Canadian wheat grower organizations, threatening to boycott all North American wheat if any biotech wheat was commercialized.  This was not because of any safety concern, but rather the fact that food companies in those countries didn't want to have to label wheat-based products as "GMO." Reluctantly the growers asked Syngenta to stop the development of their disease resistant wheat. Ironically, this is a case where a GMO opposition "fostered monoculture," when biotechnology could have enhanced rotational diversity.  The wheat growers of the US, Canada and Australia have pledged to do a simultaneous release of biotech wheat in the future so that they can avoid this sort of extra-regulatory blockage.

How Could The Corn Belt Rotation Be Diversified?

First of all, the corn/soy rotation in the corn belt is a highly successful production system.  It also includes enough genetic diversity within those species to continue to perform.  That said, some additional diversity would be a good thing. Scab-resistant wheat would both reduce risk and increase private investment in that very important and highly traded crop while simultaneously diversifying the rotation.  Another excellent way to get the soil quality benefits of rotation is to add a winter cover crop (see Midwest Cover Crops Council).  It is actually best for the soil to have something growing as much of the year as possible, and cover crops can also include a legume to make nitrogen for the next season or a grass to scavenge any excess fertilizer when that is an issue.

Probably the best way to facilitate more rotational diversity would be through education of the absentee landlord community.  Much of the land in the Midwest is held in trusts for the families who have long since migrated to the cities.  Typically all they do is collect the rent checks through a farm management company.  If those families could be educated about sustainable cropping practices, they might be willing to engage in re-designed leases designed around medium to long-term economics rather than the typical annual, cash lease.  What is needed is a way to give the grower/renters the incentive to implement the practices that might not optimize income for each year, but which lead to improved soil quality over time which in turn leads to higher income potential and more protection from drought (e.g. no-till, cover cropping, controlled wheel traffic and more diverse rotations).  The very real benefits of such a system would flow to the land-owner - increasing the value of the asset.  It would be far more constructive to find creative ways to share that value between farmers and landowners rather than to worry about "monocultures."

Corn harvest image from the United Soybean Board
Planting graphs based on data from USDA-NASS Quick Stats
Rainfall distribution graph based on NOAA National Climatic Data Center information
Fusarium image from Wikipedia