Healing the ear:
investigating corn resistance
to a fatal fungus
By Carol Crabbe

OTTAWA — Linda Harris has always been interested in learning "how life works." As a result, she has been doing scientific research since the late-'70s.

Gibberella ear rot, caused by the fungus Fusarium graminearum

Her first published work was a paper on the feeding habits of the white pine weevil – research she conducted while an undergraduate student at Simon Fraser University in British Columbia. From there, she's worked on various subjects within genetics and molecular biology

Now, Harris has moved east to the Central Experimental Farm to pursue her interest in plant-pathogen interaction and do reseach onplant disease caused by the fungus Fusarium graminearum.

Fatal fungus

This fungus, usually called Fusarium, causes cereal plants like wheat, barley and corn to go mouldy and dangerous for humans and animals to eat. Harris is working with other researchers at the Farm's Eastern Cereal and Oilseed Research Centre to find out more about the disease and its effect on corn.

Fusarium causes an increase in deoxynivalenol (DON) – a toxin that is dangerous for humans to consume. DON is also known as the vomit toxin, because it causes animals to throw up. Other toxins can also cause abortions in animals.

Fusarium enters corn through the silk tassels on the ear or directly through "wounds" or holes made on the corn's surface by insects and birds.

According to Harris, this fungus does well in temperate climates, which is why it is so prominent in parts of Canada. Fusarium also needs a humid environment to develop and finds a perfect atmosphere in the parts of Canada where corn is grown.

Corn also has limited resistance to Fusarium so that large yields of the crop can become useless for human and animal consumption, and cost farmers millions of dollars in losses.

Finding out about Fusarium

Harris studies the genes of the corn plant and the proteins these genes produce to find out what happens when the fungus attacks a plant.

To do this, Harris and her fellow researchers first grow Fusarium in V-8 juice. The V-8 juice has nutrients the fungus needs to grow, Harris says, so its an ideal environment The next step is to infect ears of corn with the fungus and see what proteins are produced in the corn, and what genes produce these proteins.

This is the basis of the proteomic and genomic study. The corn used for these experiments is grown on the Farm. It is important to find out about the genes in the plant, Harris says, because in each ear of corn, there are two kinds: genes that are "turned on" when Fusarium attacks and ones that are "turned off."

Pictures of genes

Microarrays are like photos of genes, and are used to find out which ones work harder when the disease attacks, and which ones work less. If a gene is "turned on" in reaction to the fungus, it produces more of a particular protein, and if it is "turned off" it produces less of that protein.

Picture of Genes: subsample of a microarray comparing the gene expression levels of thousands of maize genes responding to Fusarium infection.

The research seems pretty basic, but Harris says this information is essential because the genes in the plant can be catalogued from this process.With this information, links can be made between resistance, genes and proteins in corn.

Further research can then be done to isolate the specific genes that cause resistance, and these genes can be reproduced to make corn plants more able to withstand the disease.

What's next?

Predictably, the groups most interested in this research are the Ontario Corn Producers Association and Ontario Pork Producers, who are funding her work along with a number of smaller groups. According to Harris, most of the corn produced in the eastern part of Canada is fed to pigs.

Fusarium research is wide ranging in Canada , some researchers focus on the fungus itself – which has already been genetically sequenced – and others, like Harris, focus on the plants it attacks.Harris says most of the previous research has been done using wheat, but very little has been done with corn.

With her research, Harris is in some way learning "how life works" and in the process, helping to heal the corn industry. One ear at a time.