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Corn Hybrids With Low Aflatoxin In Grain

Don White
Don White
Professor of Plant Pathology
Department of Crop Sciences
(217) 333-1093; donwhite@illinois.edu
Torbert Rocheford Torbert Rocheford
Associate Professor of Plant Genetics
Department of Crop Sciences
(217) 333-9643; trochefo@illinois.edu

History repeated itself in 2002 when the drought conditions in southern Illinois favored Aspergillus ear rot and aflatoxin contamination of grain. As most know, grain with greater than 20 ppb aflatoxin cannot be sold in interstate commerce. Therefore, many grain elevators rejected grain with greater than 20 ppb aflatoxin.

Once again, growers are asking, “Which hybrids are resistant?” The answer to the question is none! We have not had acceptable levels of resistance in commercially used hybrids in Illinois at any time in the past or present. High levels of resistance can only be found in late maturing, low-yielding, southern adapted germplasm. Hybrids made using inbreds derived from southern germplasm are usually unacceptable to farmers in the Midwest because of the late maturity, low yield, and so on. Additionally, there presently is no market advantage for a commercial seed corn company to cross resistance into commercially usable materials. That’s because Aflatoxin is only a problem in years with drought growing conditions, and hybrids with resistance would need to compete on the basis of yield, etc. in all but a few years.

Figure 1. Resistant (top) and susceptible (bottom)
reactions to Aspergillus ear rot following inoculation.
The resistant is from our studies, and the susceptible
is a commercially used hybrid.

Genes for resistance must be moved from unadapted material into Corn Belt germplasm, thus establishing genes for resistance in germplasm used by breeders to create hybrids for the future. This will likely only be done by the public sector. But there is little or no commodity funding of corn pathology/breeding, because most people believe that all research is being done by commercial seed companies.

We have been working on resistance to Aspergillus ear rot and the production of aflatoxin since 1989. The drought of 1988 and serious aflatoxin problems created interest in funding from Senator Dick Durbin. He sponsored a “Special Grant” that funded much of the initial work for a number of years. Until recently, we had solid funding from the USDA/ARS Aflatoxin Elimination Program.

Since 1989, we have identified sources of resistance and molecular markers associated with genes for resistance. Currently, we are working with two sources of resistance. One inbred Mp313E (from Mississippi) has resistance genes located on chromosome arm 4. We are crossing that chromosome arm into FR1064, a commercially used inbred. In evaluation of early generation backcrosses, FR1064 and related lines have aflatoxin levels of 650 to 700 ppb aflatoxin following inoculation. Backcrossed-two lines with agronomic characters similar to FR1064 have levels of 160 to 300 ppb. We may be able to reduce aflatoxin contamination in some environments by 50 percent with this single chromosome arm.

We also are working with inbred line Tex6, which was selected by D. G. White at the University of Illinois from a population once grown in Texas. With this line, we have genes for resistance located in several chromosomes, most notably chromosomes 5 and 10. Because the genes for resistance are on different chromosomes from the two different sources, they are likely different genes, and pyramiding these genes together into a common background could result in even lower levels of aflatoxin.

Our ultimate goal is to cross genes with resistance into commercially usable inbreds that could serve as sources of resistance for commercial breeders. Along with the information on molecular markers, crossing resistance into the Midwestern hybrids would not be extremely difficult. We could produce levels of resistance that reduced aflatoxin by up to 80 percent. That resistance, in conjunction with the grain cleaner, should result in grain below 20 ppb aflatoxin in most all years in Illinois.

Currently, the only limitation on progress is funding, which could be enhanced if Illinois farmers became involved in the USDA/ ARS Aflatoxin Elimination Program.

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