University of Guelph researchers have found corn silks naturally contain diverse microbes, a finding that may point to a new strategy to help protect cobs from fungal infections.
Why it matters: The discovery may improve breeding and farming practices to avert costly and harmful fungal outbreaks.
The study was led by Dr. Manish Raizada, a professor within the Department of Agriculture at the University of Guelph.
The normal function of silks is to facilitate seed formation, as pollen grains from tassels float to the silk and then move down the silk to the cob where fertilization occurs and kernels are formed.
This also creates a conduit for fungal pathogens that seek abundant nutrients and moisture.
“Many pathogens, such as fusarium, have figured out that if you go up through the silks you will end up in a future developing seed,” says Raizada. “It’s a free passage along the silk road.”
Raizada’s lab focuses on finding beneficial microbes for crops. Many years ago researchers found that some bacteria from seeds and roots when sprayed onto silks helped suppress fusarium and DON mycotoxin.
“It dawned on me, what if plants had actually put protective bacteria microbes in the silks, to begin with? It seemed like something natural selection, or farmer selection, over time might have happened.”
Fusarium enters the crop after fertilization and before the silks die. Researchers found that pollinated silks contain 5,000 different species of bacteria.
“We were shocked, at the level of diversity. Again, this is the pollinated silks.”
To test the effects of fusarium infection, the team compared microbe populations between silks treated with fusarium and untreated.
In the treated plants, many rare bacteria disappeared from the microbiome. Yet 10 to 15 kinds of bacteria increased in numbers after infection.
“This diversity was greatly reduced in terms of the microbiome, but the total number of bacteria went up, it actually doubled. What’s going on with the silks is not random, it’s quite reproducible and so we think those bacteria that go up are somehow protecting the silks or damaging the fusarium.”
Raizada’s lab is now testing whether these bacteria, when sprayed separately onto silks, can protect against fusarium attacks.
“Now that we have revealed that this microbiome exists and have pointed out which bacteria are helpful, there is an opportunity through sprays or breeding to ‘stack’ good bacteria.”
The lab also found that the types and abundance of bacteria changed seasonally, as does the risk of the fusarium with changing weather patterns from year to year. This may be part of the equation.
“If we can understand which bacteria a plant needs to protect itself against fusarium, that is something that potentially we can breed for,” says Raizada.
If they can isolate some of these bacteria, a spray may be developed to either coat the seeds or be directly applied to silks. The other possibility is breeding.
“What we are seeing is we are now identifying pieces of bacterial DNA, and other bacteria that breeders could potentially select for to stack beneficial bacteria and perhaps to stabilize the ear from year to year.”
These findings are creating a new tool for producers because corn is beginning to develop resistance to fungicides on the market.
As well, fungicides are not providing efficacy against mycotoxins.
“Perhaps we could take an integrated approach. Because we are focusing on the bacterial microbiome they won’t be susceptible to fungicides. You should be able to stack the bacteria with the fungicides,” says Raizada.
“Microbiome-assisted breeding, some fungicides and bacterial sprays is what will provide complete durable resistance across years, across genotypes, and environments.”
Organic producers are another market because they can use bacterial sprays but not fungicides.
Previous studies showed that the use of biologicals on crops can be difficult.
“I don’t want to say there are no downsides to this. The traditional complaint about the use of bacteria is that they are not stable. They may not work well across different varieties, different environments or temperatures.”
If stable breeding can solve this problem, it is ultimately a much better solution than the use of bacteria.
This project was funded by the Natural Sciences and Engineering Research Council, the Ontario Ministry of Agriculture, Food and Rural Affairs, Grain Farmers of Ontario, and Ontario Genomics.