The spring breeze is not just pollen. Just as some human viruses spread during reproduction, plant viruses can use pollen to move from flower to flower. Research y The nature of communication shows how many viruses are transmitted by pollen, and suggests that human activities may contribute to their spread.
Tia-Lynn Ashman, an evolutionary ecologist at the University of Pittsburgh, and her colleagues used genetic sequencing to catalog viruses on pollen of wild flowers from four different environments: California meadows, the California coast, agricultural territory in Pennsylvania, and the Appalachians. The team identified 22 known viruses, some of which have a serious impact on crops. They also found evidence of hundreds of viruses that scientists have never seen.
The results are consistent with those in microbiology, says University of Florida virologist Amit Levy, who was not involved in the study: “There are far more viruses everywhere than we expected.”
The team also found an interesting correlation. Flowers from the farm plot carried genome fragments from more than 100 different viruses, while flowers from California meadows (where human activity is lowest among the study areas) had only about a dozen. Other sites had an intermediate variety of viruses. Researchers believe that the uniformity of plants in the fields may encourage more viruses to inhabit these areas – once the virus develops to infect crops, it finds many compatible hosts.
Although this link is preliminary, Levy says it makes sense that industrial agriculture can breed plant pathogens. When plants are packed together, “there is no social distance between crops”.
Ashman wonders whether bees, which are often bred by farmers, can also worsen the spread of the plant virus in agricultural areas. Honey bees are less picky about which plants to visit than most local bees, potentially carrying viruses between wildflowers and crops.
Hernan Garcia-Ruiz, a virologist at the University of Nebraska-Lincoln who was not involved in the new study, says it caught his attention because the authors found many viruses even in plants that didn’t seem sick. But such microbes may not be as benign when transmitted from wild plants to crops. Garcia-Ruiz refers to the sugar cane mosaic virus – a serious causative agent of sugar cane and corn that lurks in wild grasses between crops. “As soon as corn becomes available, insects carry the virus back to corn,” he says.
Ashman agrees that it is important to understand the impact of viruses on a variety of plants, especially when people are encouraged to spread from natural habitats to agriculture and back. As a scientific hypothesis, she considers this prospect “scurvy” but “perhaps scary.”