Pollen Grains Carry Hundreds of Plant Viruses

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There is more to pollen than riding on a springtime breeze. Plant viruses can ride on pollen, just as human viruses spread when they reproduce. A study in Nature Communications shows how plentiful pollen-borne viruses are–and suggests that human activity may help them spread.

University of Pittsburgh evolutionary ecologist Tia-Lynn Ashman and her colleagues used genetic sequencing to catalog viruses on wildflower pollen from four different environments: California grasslands, the California coast, an agricultural area in Pennsylvania and the Appalachian Mountains. The team found 22 known viruses–some of which have serious effects on crops. They also discovered evidence of hundreds more viruses that scientists had never seen before.

The results match microbiology results, according to Amit Levy, University of Florida plant virusologist: “There are just way more viruses all around than we expected .”

The team also discovered a fascinating correlation. Flowers from the agricultural site carried genome snippets from more than 100 different viruses, whereas flowers from the California grasslands (where human activity is lowest among the areas studied) had only around a dozen. Other sites had intermediate viral diversity. Researchers believe that plant homogeneity in crop fields could encourage more viruses into these areas. Once a virus develops, it will find many compatible hosts.

Levy believes that industrial agriculture could breed plant pathogens. Although this is a preliminary link, Levy states that it makes sense. “There’s no social separation between the crops .”

because they are all packed together.”

Ashman wonders whether honeybees, which are often bred by farmers, might also contribute to plant virus spread in agricultural areas. Honeybees are less picky about which plants they visit than native bees and could carry viruses between wildflowers or crops.

Hernan Garca-Ruiz, a University of Nebraska-Lincoln virologist, said that the new study caught his attention because it revealed a multitude of viruses in plants that were not sick. These microbes could be transmitted from wild plants to crops, which may make them less benign. Garcia-Ruiz mentions the sugarcane mosaic virus, a serious pathogen of sugarcane and corn that hides in wild grasses between crop seasons. He says that insects can move the virus back into corn as soon as it is available.

Ashman agrees with the importance of understanding viruses’ effects on plants, especially if humans encourage spread from natural habitats to agriculture. As a scientific hypothesis, she finds this prospect “tantalizing”–but “possibly frightening.”

This article was originally published with the title “Pollen Passengers” in Scientific American 326, 5, 18 (May 2022)

doi: 10. 1038/scientificamerican0522-18b

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