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Developing a test for fusarium in corn

Researcher used 2006 corn crop as guide.

Fusarium in corn, which causes gibberella ear rot, can hurt yield and quality but also seriously affect the quality and nutritive value of livestock feed.

The 2006 corn crop in southwestern Ontario may be one that growers and livestock producers would like to forget because of the high levels of ear moulds and mycotoxins. It is providing researchers with an opportunity to gain a better understanding of the complexities of fusarium.

Following that growing season, the Canadian Seed Trade Association agreed to release corn samples from the Ontario Corn Performance Trials for use in a fusarium research project at the University of Guelph, Ridgetown Campus. The researchers, led by Dr. Art Schaafsma, are developing reliable mycotoxin detection tests that will benefit several segments of the industry, from plant breeders to end-users of corn.

Gibberella zeae is the most common and important ear mould in Ontario. It is the sexual reproductive stage of Fusarium graminearum. The fungus also infects small grains such as wheat, where it causes Fusarium Head Blight. Not only does Gibberella ear rot raise economic concerns because of potential yield and quality losses, there is also the anxiety over the ability of Gibberella zeae and Fusarium graminearum to produce damaging mycotoxins, most notably deoxynivalenol (vomitoxin or DON) and zearalenone. The appearance of the substances in the crop can create livestock feed and food safety problems and serious economic consequences.

Dr. Victor Limay-Rios, a research associate, who is developing the tests, says that because of the potential risk to the food supply, measures have been set up in different countries to monitor and control mycotoxin levels. Furthermore, the limits of these substances in traded goods are becoming more restrictive. “Countries have different guidelines and different limits for toxins, using these as a non-tariff barrier to trade,” says Limay-Rios.

Ethanol production from corn is also playing a role in the need for a reliable test. During the production process, one-third of the grain is used to produce ethanol, another third produces carbon dioxide and the other third produces distillers dried grains with solubles (DDGS). However, the fermentation process in an ethanol plant does not destroy mycotoxins that may be present. In fact, Dr. Limay-Rios says the mycotoxins are condensed by a factor of three: if the corn contains 1 part per million (ppm) of a mycotoxin, the DDGS produced from that corn will contain approximately 3 ppm. While DON is mild compared to other toxins, feed containing a small amount can adversely affect weight gain of the animals. For adult pigs, calves, lactating cows and lambs, along with a few other species, the recommended maximum level is 1 ppm. For young pigs, the accepted level is lower at 0.5 ppm. For cattle, adult sheep and poultry, the maximum level is higher at 5 ppm.

Is fusarium in corn an increasing problem in Ontario? Dave Harwood, technical services manager for Pioneer Hi-Bred, says that is challenging statement to qualify. “It’s a problem every year in pockets, and to the extent to which those pockets expand or how extensive it is in any given year varies,” explains Harwood. “What we saw in 2006 in the corn crop was far more than in pockets and widespread throughout much of southwestern Ontario. A year severe as that one was probably 20 years before that.”

 

Research into detecting fusarium could help all facets of the grains and oilseeds sector, from production in the field to point of delivery and purchase.

Harwood says another challenge is screening hybrids for their reaction to fusarium. In order to make genetic improvements, Harwood says the disease has to be reliably exposed to the crop, which is not easy to do with fusarium. “With many diseases, you can do that artificially, and quite reliably, and it really reflects what goes on in the real world,” says Harwood. “But with Gibberella ear rot, that’s not the case. The artificial infestations often create a reaction that is not predictive of the real world.”

Dr. Limay-Rios concurs with Harwood’s assertion. He recalls a study in which researchers put vomitoxin in the animal feed and compared the results with feed that was naturally contaminated at the same level. “The effect on the animal was dramatic in the natural case, which means that vomitoxin or DON alone cannot explain why,” says Limay-Rios, who adds that there are masked mycotoxins that are not being properly identified.

Identifying all these mycotoxins is one key objective of the project, which Limay-Rios breaks into two main parts. In the first, the researchers are trying to develop a laboratory method that uses liquid chromatography mass spectrometry (LC-MS) to simultaneously detect chemically diverse mycotoxins in a single sample preparation.
 
The second part involves developing a near infrared (NIR) spectrometry technique for a simple, rapid and cost-effective estimate of DON in wheat and corn grain using LC-MS as a wet chemical reference method. NIR is a correlative technique in which reference data is regressed against spectral data for future predictions of DON. NIR is routinely used on grains delivered to elevator terminals to estimate moisture contents and quality characteristics where results are obtained within minutes. “If we develop an NIR calibration equation that could be introduced in their existing machine, we can potentially estimate DON level in the grain sample in real-time,” says Limay-Rios. “So that has huge potential.”

Limay-Rios says the test is still at the experimental stage of development in wheat and soon they will be expanding to corn, estimating that it would take at least two years before it would be commercially validated. According to Harwood, the development of an accurate analytical technique would be welcome because another challenge presented by Gibberella ear rot is that the grain could have clear evidence of mould, but the DON levels are relatively low or vice versa. “It would be useful in everything from screening hybrids to grain at point of delivery and purchase,” says Harwood. “It’s the level of vomitoxin that is the issue, so having a test, rather than relying on visual assessment of the grain, would be highly preferred.”