Researchers probe new means of controlling crop pest with bacterium

Researchers have discovered a bacterium in a plant-parasitic roundworm and hope it could lead to an environmentally friendly way of controlling the crop-damaging pest.

The bacterium is a strain in the genus Wolbachia, which, as one of the world' s most widespread endosymbionts, namely organisms that live within other organisms, is present in roughly 60 percent of the globe's arthropods, among them insects, spiders and crustaceans.

And the roundworm, Pratylenchus penetrans, is one of the "lesion nematodes," microscopic animals that deploy their mouths like syringes to extract nutrients from the roots of plants, damaging them in the process. This particular nematode uses more than 150 species as hosts, including mint, raspberry, lily and potato.

Depending on the host species, Wolbachia can be an obligate mutualist that the bacteria and the host need each other for survival, or a reproductive parasite that manipulates the host's reproductive outcomes in ways that harm the host and benefit the bacteria. Parasitic Wolbachia can cause its host populations to heavily skew toward female.

In the case of the crop-pest nematode that postdoctoral scholar Amanda Brown in the Oregon State University (OSU) Department of Integrative Biology and her colleagues studied, the bacteria-host relationship appears to not be one of obligate mutualism, as many examples of non-infected worms have been found, meaning the worm doesn't rely on Wolbachia to survive.

The discovery of Wolbachia in Pratylenchus penetrans, according to the researchers, opens up the potential for managing the roundworm's population via biocontrol rather than environment-damaging fumigants, such as methyl bromide, that are being phased out by the U.S. Environmental Protection Agency.

"We can use what's already infecting them against them," said Denver, the lead author on a study published in the journal Scientific Reports.

Nematode biocontrol would involve releasing Wolbachia-infected worms into farm fields whose worm populations weren't infected. From there, a couple of situations might arise: the bacterium could hinder the worms' ability to reproduce; or, it might force the worm to devote energy to dealing with the bacterium, effectively distracting it from being as damaging to the crops as it otherwise would be.

Wolbachia has been used as a biocontrol strategy in Colombia and Brazil, where infected mosquitoes were released to control the Zika, dengue and malaria viruses. Mosquitoes are a vector for those diseases, but Wolbachia-infected mosquitoes pass the bacteria to their offspring, who lose their ability to transmit the diseases. Wolbachia also can interfere with the mosquitoes' ability to reproduce at all.

"We can see where all of that goes and learn from it to help our decision making on how the strategy might get deployed to control the population of plant-parasitic nematodes," Denver was quoted as saying in a news release from OSU. "One big thing with nematodes is the load. Many crops have some, but once you get above certain thresholds, fields go down and there are economic losses." Endit