New University of California, Riverside studies show native plants and crops grown side-by-side can share diseases that are detrimental to plant health and growth.
Despite pollination and biodiversity benefits, there are downsides to growing native plants alongside non-native crops. According to two new University of California, Riverside (UCR) studies, both the native and non-native plants attract and then share pests that spread diseases, negatively impacting each other.
“We have changed the landscape, and it’s created opportunities for pathogens to thrive,” UCR entomologist Kerry Mauck, co-author of the studies, said according to a UCR news release.
“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.”
One study, published in the journal Phytopathology, highlights the presence of a bacterial pathogen, Candidatus liberibacter solanacearum (CLso), in wild California plants. Transmitted via small flying insects called psyllids, this bacteria can negatively impact nightshade species like tomatoes, potatoes, and peppers. For example, it causes zebra chip disease in potato crops, which deforms tubers and can reduce crop yield up to 90 per cent. The disease sprang up suddenly in the 2000s and spread quickly.
“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 in the release.
To find an answer, Mauck and his team visited multiple UCR natural reserves and wildland areas. There, they took samples of plants in the nightshade family, as well as looking at preserved specimens that dated back 50 years.
They found that the pathogen existed in nearly 20% of the samples but not in the form known to infect agricultural crops. Further, the pathogen seemed not to harm the native plants that it inhabited, while the form that affects crops does cause disease in native plant species. With this understanding, the team concluded that the CLso variants found in native species are not the same variants found in crops, meaning that the pathogen has mutated to affect host plants differently.
The research team recently received funding from the U.S. Department of Agriculture, with the aim of understanding on a molecular level why and how the pathogen mutated to be able to affect crop plants.
In a related study published in Phytobiomes Journal, Mauck’s team studied the transfer of viral pathogens from crops like squash, melons, and potatoes to wild squash plants in UCR reserves.
“Crops such as squash, melons, and potatoes attract aphids and whiteflies that can spread viruses from crops to wild plants,” Mauck said. “A lot of the viruses in crops are very new to the area, being introduced only in the last couple of decades. If these viruses are moving out of crops and into wild areas, the native plants could be bombarded with new pathogens they’ve never encountered before.”
The researchers found that over 80% of wild squash they sampled, as well as Anza-Borrego Desert State Park, were infected with a virus not native to California. The virus targets the roots of the plants – a major problem for any plant growing in the hot, dry Southern Californian climate.
“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.”
Both studies underscore the importance of collaboration between land managers, growers, and plant enthusiasts to prevent the introduction of harmful pathogens to new environments.
“Plant pathogens can be anywhere. Whenever we move plants for trade, there is the potential for bringing in pathogen hitchhikers as well. We need to make sure we’re moving only plant material that doesn’t contain these unwanted guests,” Mauck said.
“Studying how plant pathogens move, live together in plants, and mutate over time can help us to achieve the goal of reducing unwanted pathogen problems both in crops and in wild plants.”
