Plant pandemic looms as pathogens move from wild plants to crops

Did you know that plants, just like humans, can fall ill, too? And much like our world, theirs is not immune to disease outbreaks and pandemics. As nature-lovers and responsible stewards of the earth, it’s vital we understand how we are unintentionally facilitating the spread of pathogens that cause “plant pandemics.”

Two recent studies from UC Riverside have revealed that native plants and non-native crops don’t play well when they’re neighbors. Both being attractive hangouts for pests, they’re unwittingly spreading diseases to each other.

Pathogen and plant health

“We have changed the landscape, and it’s created opportunities for pathogens to thrive,” said UCR entomologist Kerry Mauck, who co-authored the studies. “We have introduced pathogens that damage native plants, and on the other side of the coin we have endemic pathogens that mutate to infect crops.”

The research has shed light on a worrying development: the presence of a bacterial pathogen affecting nightshade plants in the wilderness of California.

This pathogen, Candidatus liberibacter solanacearum or CLso, is a close relative of the one causing citrus greening disease, a deadly disease for citrus plants with no known cure.

CLso, transmitted by a small flying insect called a psyllid, is the culprit behind the zebra chip disease in potatoes. It deforms the tubers, rendering them unmarketable and reducing crop yields by a staggering 90%.

“We wanted to know, why did this thing show up so suddenly in the U.S.? The psyllid vector has been here. It’s native. We wondered if maybe the pathogen has also been here longer than we realized,” Mauck said. 

Through their exploration of various UC natural reserves and inspection of preserved herbarium specimens dating back to the 1970s, they made a startling discovery.

CLso was present in 15-20% of the plants they examined. But here’s the twist: the variants don’t harm the plants they inhabit and are not of the infectious type impacting crops.

Pathogen mutation

Having unveiled the difference between the wild and crop-infecting pathogen, the researchers have earned funding from the U.S. Department of Agriculture to dive deeper into this disturbing mutation.

They’re keen on decoding how this pathogen evolved from being benign to problematic and what lies at the crux of pathogen-plant interaction.

A second, related study published in the Phytobiomes Journal focused on the viral pathogens’ movement from crop fields to wild plants.

“Crops such as squash, melons, and potatoes attract aphids and whiteflies that can spread viruses from crops to wild plants,” said Mauck.

Pathogen spreading in plants

A big worry is that a lot of these viruses were introduced in the last few decades. These native plants may be coming face-to-face with pathogens they’ve never met before. It’s like getting an unexpected and unwelcome guest at your door.

A stunning 80% of wild squash plants sampled were found infected with a non-native virus, cucurbit aphid-borne yellows virus, or CABYV. These viral infections stunt the growth of roots – a critical issue in Southern California’s arid and hot summer conditions.

“If the plants can’t make roots, they can’t access groundwater or store water in their roots. And wild squash are among the few plant species growing and providing resources in summer, so they’re relied on a lot by other organisms,” Mauck said.

“They’re highways for ants. They provide nectar and pollen. The seeds are eaten by endangered mammals. They’re critical.”

Preventing plant pandemics

These studies emphasize the pressing need for land managers, growers, and plant enthusiasts to join forces in curbing the introduction of plant pathogens into new areas.

When we consider plant trade, there’s more at stake than just the plants themselves. We unknowingly transport unwelcome ‘plant-demic’ instigators along with them. Mauck stresses, “We need to make sure we’re moving only plant material that doesn’t contain these unwanted guests.”

Knowledge truly is power. By understanding how plant pathogens move and mutate, we can work towards reducing unwanted pathogen problems, safeguarding both our crops and wild plants.

The study is published in the journal Phytopathology.

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