Bt Corn - Increased Disease Control

Bt CORN
Increased Disease Control
By Albert Tenuta, Field Crop Plant Pathologist, OMAFRA, Ridgetown College

If you read newspapers, watch television, listen to the radio or surf the net you quickly realize that Bt corn and other genetically enhanced organisms are still very much in the news. However, these reports often ignore and misrepresent the “science” behind this new technology. In fact, some of these reports would have you believe that this technology has just recently sprung-up, rather than being the product of decades of biotechnological research.

As a plant pathologist, a direct benefit of Bt corn that I believe must be better promoted is its influence on reducing the incidence of corn ear mould diseases. These fungi have the ability to produce mycotoxins that can impact livestock and (in some cases) human health. Reductions in mycotoxin levels and the resulting increased health benefits will not only serve corn producers, but all consumers...regardless of where they live.

Bt Corn Reduces Fusarium Ear Mould/Mycotoxins

A recent master’s thesis by Tracey Baute (University of Guelph), under the supervision of Dr. Mark Sears, found that Fusarium ear moulds associated with ear damage from corn borer feeding was significantly reduced in Bt hybrids (Figure 1). The same result was observed in a number of U.S. studies (Iowa, Illinois, New York and North Carolina).

The U.S. studies went one step further and examined the relationship between Fusarium infection, mycotoxin production and corn borer damage (Figure 2). They concluded that where the Bt protein is expressed and how long it was present in the plant is crucial. Those events (lines) that provide season-long protection and produce the Bt protein in all plant parts including the grain (BT 11 and MON 810) had significantly lower European corn borer larvae feeding damage than events that produced the protein only in green tissue (DBT 418 and 176). Subsequently, the result of reduced larval feeding damage was significantly lower Fusarium infection and mycotoxin levels. Dr. Art Schaafsma (Ridgetown College, University of Guelph) is investigating Fusarium and mycotoxin production in Bt and non-Bt hybrids in Ontario as well. This information will be included in a future Ontario Corn Producer article.

The length of time that the Bt protein is expressed in the plant is important when corn borer development and activity are considered. Second generation and late first generation corn borer activity significantly influence Fusarium ear rot severity. First, the longer the plant and kernels are protected, the fewer potential sites (wounds) for ear rot fungi to enter and infect.

Secondly, corn borer larva can be a vector for various disease-causing fungi, including Fusarium. The larvae carry Fusarium spores from the surface directly on or into wounded kernels, where infection can begin. Finally, larvae feeding cause stress on the corn plant, making it more susceptible to infection and disease. So, minimizing corn borer damage with Bt technology should be considered an important management tool in the fight against ear moulds and mycotoxins.

Editor’s Note: Corn growers should be aware that Bt corn is not resistant to Fusarium ear mould, which can also infect the plant through the silk channel. However, these data indicate that reducing the number of corn borer wounds can also significantly reduce the ear mould, and resulting mycotoxins.

Corn Borer Resistance Management
In Canada, an insect resistance management (IRM) strategy has been implemented. These guidelines, developed by the Canadian Corn Pest Coalition and the Canadian Food Inspection Agency, recommend that each producer adapt an IRM strategy to ensure long-term performance of transgenic crops and delay the development of corn borer resistance to Bt corn. This specific resistance management strategy involves exposing one portion of the corn borer population to Bt plants with high concentrations of the Bt protein, while maintaining another part of the population in a refuge where the pest does not encounter any Bt protein. Although Canada has been following these guidelines for some time, the U.S. Environmental Protection Agency recently accepted these same recommendations for U.S. corn producers and seed companies.

Key steps in an IRM plan are:

Grow Bt corn hybrids in fields that are at risk from European corn borer damage.
Keep careful and accurate records as to where Bt and non-Bt corn hybrids are planted.
Establish refuge areas consisting of at least 20 per cent non-Bt corn hybrids. This will ensure an adequate supply of ECB moths that have not been exposed to the Bt Cry protein. The 20 per cent non-Bt corn refuge can be implemented in various patterns such as complete fields, blocks, headlands or alternate strips (six rows wide or greater). The refuge must be within 400 metres (a quarter-mile) of any Bt corn fields.
Continue to scout for corn borers, other insects and disease problems in both Bt and non-Bt fields.
Monitor for resistance in European corn borers to Bt corn.

Bt Corn Growers’ Handbook
A new publication “A Grower’s Handbook: Controlling European Corn Borer With Bt Corn Technology” – was recently made available to Canadian corn producers to help answer questions and provide background information concerning this new technology. If you haven’t already received a copy, contact your seed corn dealer, the OCPA Web Site at http://www.ontariocorn.org/btguide.html #or the Ridgetown OMAFRA office at 519-674-1690.