UC Davis Research Reveals a New Way to Fight Grey Mould

You have almost certainly encountered Botrytis cinerea, whether or not you recognised the name. It is the grey fluff appearing on blueberries the day after purchase, the mould taking hold on tomatoes, and the soft rot spreading through orchids.

Grey mould infects hundreds of plant species and is responsible for an estimated 5% to 10% of fruit and vegetable crop losses worldwide.

For decades, scientists have sought to breed resistant crops, with limited success. Fresh research from UC Davis indicates that they may have been tackling the wrong question.

Two connected studies headed by Dan Kliebenstein, a professor in UC Davis’s Department of Plant Sciences, challenge two assumptions that have quietly shaped crop-disease research for years.

Plants use different defence strategies

Scientists long believed that different plants attacked by the same fungus would deploy broadly comparable defences.

Under that model, discovering how one plant withstands grey mould should have allowed researchers to apply the lesson to another.

Kliebenstein illustrates the idea vividly: researchers once assumed that plants might decorate the Christmas tree differently, but that it would still be a Christmas tree.

Yet, as Kliebenstein puts it, “for some plants, it’s not a Christmas tree at all. It’s a saguaro cactus.”

How plants respond to grey mould

When the researchers investigated how plants truly reacted to grey mould infection, they discovered that every plant deployed a fundamentally distinct defence.

This held true for comparisons between both closely related crops and more distantly related plants.

When each plant behaves entirely differently while defending itself, insights from one plant’s resistance cannot simply be carried over to another.

“It’s why we could never figure out how to move information from one plant to help another become resistant, because what one plant is doing doesn’t actually do anything for the other plant,” Kliebenstein said.

A fungus with intelligence

The findings of the second study surprised even the team behind it.

Rather than using one universal method to infect plants, grey mould seems able to detect the plant on which it is growing and alter its attack to suit.

“The pathogen is like a human,” Kliebenstein said. “At some level, it knows it’s attacking a strawberry, and there’s one set of things it should do.”

“If it’s attacking a tomato, it knows it’s attacking a tomato and it decides to do something completely different.”

The fungus adapts its attack

In practice, the fungus appears to be “reading” a plant’s chemical defences before selecting a customised counter-strategy.

It is not a crude tool; it is closer to a burglar assessing a building before choosing how to enter it.

That substantially alters the situation. If the fungus can tailor its attack to every plant it meets, breeding plants with more powerful versions of their current defences may work only until the fungus learns to bypass them.

A different approach to the problem

Taken together, the two studies indicate that the field has been pressing against an unseen wall - and that a route around it may exist.

“They suggest that everything we’ve been trying on the plant or fungus side is probably always going to be doomed to fail, and instead we should be looking at how the pathogen knows what it’s attacking,” Kliebenstein said.

If scientists can find the particular genes the fungus uses to identify the plant it faces, they may be able to disrupt that recognition mechanism.

They could chemically or genetically “confuse” the pathogen, preventing it from reading the plant it is attacking.

A confused fungus, unable to produce a tailored response, would be much more susceptible to the plant’s own natural defences.

“We’ve been hitting ourselves against a brick wall and we just never thought about this,” Kliebenstein said. “Now we might have realized – oh, if we take two steps to the right, the brick wall ends.”

Beyond any single crop

The potential value of this method extends beyond an individual crop.

Existing resistance breeding must be developed separately, plant species by plant species.

In theory, an approach aimed at the fungus’s recognition system could work across multiple crops at once, as it targets something the fungus does irrespective of the plant on which it grows.

It will not be achieved quickly. Finding the relevant genes, determining how to disrupt them, and establishing whether the disruption performs under real agricultural conditions will all require time.

Still, after decades of only modest gains from methods that now appear to have overlooked a vital part of the picture, a truly new avenue is significant.

Both studies were published in the Proceedings of the National Academy of Sciences.