Is Lack of Genetic Diversity and Crop Diversity Accelerating a New Epidemic in Corn?

This year US farmers are seeing a devastating disease in corn that is reducing yields by as much as 50% on some farms. Goss’s Bacterial Wilt (named for the Nebraska pathologist who discovered it) has historically only been found in a few counties in Nebraska and Colorado, but this year it is appearing as far north as Minnesota, south as Louisiana and Texas, and east into Iowa, Illinois, Idaho and southern Wisconsin.


When fast spreading infestations like this emerge agronomists look for the environmental conditions that favor the spread. Goss’s wilt favors wet conditions, and this season has been ideal for the spread, but there are also human factors at play in the disease’s new found success.

One factor is certainly farmers reducing rotations and diversification of crops, and planting corn year after year, creating a “green bridge” from the residual corn plants and plant matter that remains in the field that provide habitat for the disease. This lack of crop diversity creates vulnerability in the field, and in rural economies.  And it’s a horrible investment in food security. If it’s a bad year for corn and the majority of acreage of a state is planted in corn, well, it doesn’t take an ag economist to tell you that farmers will need widespread taxpayer bailouts to cover their losses. Lack of diversification in crop production is certainly a cause in Goss’s wilt, and a cost to all of us.

But genetic diversity in the field is also a likely contributor. This fast spreading outbreak of Goss’s wilt also has all the red flags that the Southern Corn Leaf Blight epidemic had in 1970, the most economically devastating crop epidemic in modern times in the United States (the blight destroyed an estimated 20-25% of the corn yield). The blight spread so rapidly because of narrow genetic diversity in corn in the US. In fact, 85-90% with one genetic “type” of corn (not one variety, but a genetic type that had a trait for cytoplamic male sterility). This type of corn turned out to be highly susceptible to the blight. While the corn breeding companies had focused their efforts on efficiency in the field and production (male sterility in the female eliminates the need to detassel female plants in hybrid corn seed production) they had inadvertently created major vulnerability to disease. An industrial approach to plant breeding that prize efficiency created a situation where diversity in the field lacked genetic resiliency and created vulnerability.

We are in the same situation today.  And it is highly likely that narrow diversity in corn is contributing to the spread of the disease. As the NYTimes reports:

“No one is certain why Goss’s wilt has become so rampant in recent years. But many plant pathologists suspect that the biggest factor is the hybrids chosen for genetic modification by major seed companies like Monsanto, DuPont and Syngenta.

“My theory is that there were a couple of hybrids planted that were selected because they had extremely high yield potentials,” said Dr. Robertson, whose research is financed by Monsanto and the Agriculture Department. “They also may have been highly susceptible to Goss’s wilt.”

About 90 percent of the corn grown in the United States comes from seeds that have been engineered in a laboratory, their DNA modified with genetic material not naturally found in corn species. Almost all American corn, for instance, is now engineered to resist the powerful herbicide glyphosate (often sold as Roundup), so farmers can kill weeds without killing their corn.”

As a member of the USDA National Genetic Resource Advisory Council I just co-authored a report to Secretary Tom Vilsack that strongly urges the USDA to  “establish a baseline assessment of and ongoing monitoring for potential crop genetic vulnerability caused by too narrow a genetic base.”  In discussions  that led up to the report the scientists and seed industry professionals on the council were unanimous in their agreement that corn and soy in the United States are “highly vulnerable” because of narrow genetic diversity, with estimates that the vast majority of US corn shares 4 or 5 parents. A representative from the biotech corn seed industry summed it up well enough, “We don’t have a clue on the current diversity of corn and soybeans extant in farmers’ field, and this is unacceptable.”

Scientists, seed industry, farmers, public policy makers and the public at large should pay attention to Goss’s Bacterial Wilt, and see it as a cautionary red flag  - it’s a flag that we will see more and more as climate change begins to stress crops and accelerate the spread of new crop diseases. We need to wake up to two very simple facts:

1) We lack crop diversity.

2) We lack genetic diversity within crop types in the field.

Lack of crop diversity in the field, and lack of genetic diversity within our crops creates vulnerability in food security, and is economically unsustainable (US taxpayers underwrite crop insurance payments for crop failures).  It’s bad science, bad business, and bad for our food future.

One reason we see this lack of diversity is the disappearance of public plant breeding programs that served regional agriculture with diverse germplasm. Our public institutions used to release finished varieties that competed with the private seed sector, giving farmers alternatives and adding to diversity. Now these same programs are primarily focused on doing basic research for the dominant biotech seed sector, no longer competing and no longer innovating. In a concentrated seed market the seed companies are working on maximizing profitability for shareholders, and in so doing cut corners in terms of providing truly regional and diverse plant genetics.

The overall solution to increasing crop diversity and genetic diversity within crops is complicated, and multi-pronged (and includes USDA-DOJ re-opening their antitrust investigation into the seed industry), but one step in the right direction is a Farm Bill that funds public plant breeding programs that produce finished cultivars for the needs of regional farmers.  We, as a public, can invest now in public plant breeding that serves diverse regional needs – or we can pay a much bigger bill in terms of food security and tax dollars when crop failures become the norm.

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