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Annual losses to aflatoxin are estimated at some $190 million. Paul Williams, USDA-ARS researcher/geneticist, and his Mississippi-based team are learning to combat the disease through corn breeding and molecular markers.
Germplasm part of solution
Unfortunately, no one has yet completely solved the aflatoxin problem.
“I think germplasm will be a part of the (eventual) system to deal with aflatoxin, not the whole thing.”
One aspect of Williams’ project is to screen new sources of germplasm to locate resistance to aflatoxin. The researchers secure germplasm from various places, including the GEM (Germplasm Enhancement of Maize) Project — which involves both public institutions and private companies — and the International Maize and Wheat Improvement Center in Mexico (CIMMYT).
“Also, exotic germplasm from other countries has been crossed with proprietary germplasm that companies have provided. We screened that looking for new sources of resistance.
“We’ve also screened old, Southern germplasm lines we could find. Old in-breds could be another source of resistance.
“So, the first thing we do is screen sources. If we find some resistance, we begin the breeding to get that into a line that could eventually be released to the public.”
In some cases, the researchers find resistance in plants that are very late or poor-yielding. Those situations may require crosses, breeding and reselection so the resistance can be moved into a more user-friendly line.
The team is also expending significant effort in identifying molecular markers — genes, or groups of genes — that control resistance.
“When we have a source of germplasm, obviously it contains something responsible for resistance. If we can identify quantitative trait loci (QTL) — groups of genes or portions of chromosomes associated with resistance — it allows a breeding program to move those into elite germplasm lines that would be useful to the corn industry. We’ve been successful with some of that.
“After that, whoever is doing the breeding can select for the molecular markers rather than have to evaluate all the germplasm in field and phenotype it for how much aflatoxin it has after infection.”
To identify the molecular markers, the researchers do field tests to assess what level of resistance different lines are showing. Then, they make crosses and assess resistance in the progeny.
One advantage of working on aflatoxin researcher in Mississippi: it’s easy to get high levels of contamination.
“That’s particularly true when you inoculate the ears with the fungus. Most years, we can rely on having hot, humid weather in the state with dry periods. That’s a given. While that’s a problem for farmers it works well for those of us researching and doing disease screenings.”