Turns out plants can recruit bacteria to fight pathogens

Researchers find corn somehow attracts fusarium-fighting bacteria

Some bacteria found on corn silk are reduced, while some proliferate when exposed to fusarium.

Glacier FarmMedia – 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.

The normal function of silks is to facilitate seed formation, as sperm, when released from pollen, will travel up the silk to fertilize the egg.

This also creates a conduit for fungal pathogens which 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,” said study leader Manish Raizada, a professor of plant science at the University of Guelph.

“It’s a free passage along the silk road.”

Raizada’s lab focuses on finding beneficial microbes for crops. Many years ago his team 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.”

When they looked further into pollinated silks — fusarium enters the crop immediately after fertilization before the silks die — they found that pollinated silks contain 5,000 different species of bacteria.

“We were shocked, at the level of diversity,” said Raizada.

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,” he said. “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,” said Raizada.

If they can isolate some of these bacteria, a spray may be developed to either coat onto seeds, or directly spray onto 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 as plants are beginning to develop resistance to fungicides on the market.

As well, fungicides are not providing efficacy against mycotoxins.

“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,” said Raizada.

“Microbiome-assisted breeding, some fungicides and bacterial sprays is what will provide complete durable resistance across years, across genotypes, and environments.”

As well, a separate market is available for organic producers as they are not permitted the use of fungicides but can use bacterial sprays.

“I don’t want to say there are no downsides to this,” said Raizada. “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.”

This article was originally published at Farmtario.

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