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Davis, California

Wednesday, October 20, 2021

Column: Worms in farms

Nematodes are some of the most important animals that we rarely ever see. They’re commonly called roundworms because, well, that’s what they look like. They’re much more diverse than you would expect, though, ranging from microscopic bacteria grazers and plant eaters to foot-long worms in the human intestine.

Howard Ferris, professor of nematology at UC Davis, focuses on the microscopic, though humans did discover the larger ones first.

“Humans have been aware of nematodes for a long time because they affected us directly,” Ferris said. “People would say, ‘What’s that wriggling in the fecal sample?'”

After people discovered nematodes in themselves, it wasn’t too long before they realized it was one of the causes of diseases in their crops, as well.

Ferris took me on a short tour of his specialty, the microscopic nematodes that live in soil. We looked through a microscope that had two separate viewers so I could watch as he showed me the worms.

The nematodes that are important to agriculture come in countless different varieties, but based on what they feed upon, the layperson can classify them: bacteria-eating, plant-eating and predatory. These differences are just as important to nematodes as the food web differences between plankton, fish and humans.

“Some [nematodes] are higher-level predators of nematodes that are plant pests; they can suppress their root-feeding prey, leading to less damage to the plant,” Ferris said.

In other words, the presence of predatory nematodes keeps the plant-eaters in check. Both the predatory and the plant-eating nematodes, though tiny, take on a complex and almost sinister appearance. In the mouth of the predatory nematode are sharp teeth; they are the lions of the nematode world.

The plant-eaters have an even stranger structure. They have what looks like a sharp pin inside of their head, called a stylet. When the nematode finds a plant cell or root that it wants, the pin ejects out of the mouth and stabs the cell, sucking in its contents. These are the plant pathogens that can cause disease in crops, from potato cyst nematodes to root-knot nematodes.

Unfortunately, the predatory nematodes that eat the plant-eaters have weaknesses in a farming environment.

“Predatory nematodes are sensitive to fertilizers and other agricultural chemicals; the chemicals dissolve water films around soil particles, which is where the nematodes live,” Ferris said. “Predatory nematodes are also intolerant to soil disturbances. Soil tillage abrades their bodies.”

According to Ferris, the plant-eaters are also stronger than their predators in the face of chemical pesticides. The pesticides negatively affect all nematodes, but the plant-eaters tend to rebound more quickly. The result is a less diverse microbial community in the soil and therefore fewer resources that the land can provide through microbial metabolism.

Ferris wants the agricultural world to change its thinking, from exterminating every living thing in the soil except the wanted crop to allowing a wide diversity of life to flourish.

“The scorched approach to agriculture results in nearly empty soil,” Ferris said. “Once you’ve annihilated the community in the soil, how do you recreate it? Once you’ve lost that soil food web, getting it back requires more effort and time than tearing it down.”

As we left his lab, we stopped by an adjacent room. It was fairly small, about twice as large as a walk-in closet, but filled nearly floor to ceiling with books and files. Ferris explained that this room was a result of farmers in Davis, years ago, wanting research on nematodes compiled for reference. The collection now contains about 15,000 reprints of research from the early 1900s to about 1990.

The room gives a glimpse of the pre-internet days before scientific journals had an effective way to gather all their research for easy access. Some of the research papers and references in here are old enough that journals didn’t bother archiving them online.

Growing up as I did on the cusp of the internet revolution, I only spent my elementary and middle school years needing to look through reference books and encyclopedias to research a topic, and I still felt nostalgic.

That feeling of nostalgia was clearly stronger for Ferris as he flipped through one of the many worn books.

“I’m forever finding stuff that I knew nothing about,” Ferris said.

AMY STEWART can be reached at science@theaggie.org.

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