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Plant virus to help farmers better manage pests

Researchers have discovered that a biological nanoparticle – a plant virus – is capable of delivering pesticide molecules deeper below the ground, to places that are normally beyond their reach. The work could help farmers better manage difficult pests.

The discovery was made by researchers at the American University of California San Diego and Case Western Reserve University. They discovered that a biological nanoparticle – a plant virus – is capable of delivering pesticide molecules deeper below the ground, to places that are normally beyond their reach.

The work could help farmers better manage difficult pests, like parasitic nematodes that wreak havoc on plant roots deep in the soil, with less pesticide.

Pesticides are sticky molecules

Pesticides are very sticky molecules when applied in the field, Nicole Steinmetz, a professor of nanoengineering at the UC San Diego Jacobs School of Engineering explained. They bind strongly to organic matter in the soil, making it difficult to get enough to penetrate deep down into the root level where pests like nematodes reside and cause damage.

To compensate, farmers end up applying large amounts of pesticides, which cause harmful residues to build up in the soil and leach into groundwater.

Tobacco mild green mosaic virus

Steinmetz and her team are working to address this problem. In a new study, they discovered that a particular plant virus, Tobacco mild green mosaic virus, can transport small amounts of pesticide deep through the soil with ease.

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A potato field is being sprayed. Pesticides are very sticky molecules when applied in the field. To compensate, farmers end up applying large amounts of pesticides. - Photo: Hans Prinsen
A potato field is being sprayed. Pesticides are very sticky molecules when applied in the field. To compensate, farmers end up applying large amounts of pesticides. - Photo: Hans Prinsen

In lab tests, the researchers attached a model insecticide to different types of nanoparticles and watered them through columns of soil.

Tobacco mild green mosaic virus outperformed most of the other nanoparticles tested in the study. It carried its cargo down to 30 centimeters below the surface. PLGA and mesoporous silica nanoparticles, which researchers have studied for pesticide and fertiliser delivery, carried their payloads 8 and 12 centimeters deep, respectively.

Cowpea mosaic virus

Other plant viruses were also tested. Cowpea mosaic virus also carried its payload 30 centimeters deep below the surface, but it can only carry a fraction of the payload that Tobacco mild green mosaic virus can carry. Interestingly, Physalis mosaic virus only reached 4 centimeters below the surface.

Tomatoes, potatoes and eggplants

In terms of safety, Tobacco mild green mosaic virus can infect plants of the Solanaceae (or nightshade) family like tomatoes, potatoes and eggplants, but is benign to thousands of other plant species. Also, the virus is only transmitted by mechanical contact between two plants, not through the air. That means if one field is being treated with this virus, nearby fields would not be at risk for contamination, researchers said.

Computational model

The team also developed a computational model that can be used to predict how different pesticide nanocarriers behave in the soil -- how deep they can travel; how much of them need to be applied to the soil; and how long they will take to release their load of pesticide.

As a next step, Steinmetz and her team are testing Tobacco mild green mosaic virus nanoparticles with pesticide loads. The goal is to test them in the field in the near future.

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