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Saturday, December 03, 2022

Study tracks plant pathogens from natural areas to leafhoppers

Phytoplasmas are bacteria that can invade the vascular tissues of plants, causing many different crop diseases. While most studies of phytoplasma begin with examining plants showing signs of disease, a new analysis focuses on tiny insects that carry infectious bacteria from plant to plant. By extracting and testing DNA from archival leafhopper samples collected in natural areas, the study identified new phytoplasma strains and found new associations between leafhoppers and phytoplasmas known to harm crop plants.

Reported in the journal Biology, the study is the first to look for phytoplasmas in insects from natural areas, said Valeria Trivelon, an Illinois Natural History Survey postdoctoral researcher who led the research with INHS State entomologist Christopher Dietrich. It is also the first to use a variety of molecular approaches to detect and identify phytoplasmas in leafhoppers.

“We compared traditional molecular techniques with next-generation sequencing approaches, and we found that the new techniques outperformed the conventional ones,” Trivelon said. He said these methods will allow researchers to target more regions of the phytoplasma genome to get a clearer picture of the different bacterial strains and how they harm plants.

“One thing that’s really novel about this study is that we focused on the vectors of the disease, the leafhoppers, and not the plants,” Dietrich said. The standard approach of looking for phytoplasmas in plants is too labor-intensive, requiring scientists to extract DNA from a plant that appears to be diseased and examine the phytoplasm, he said.

“But even when you identify the phytoplasma, you don’t know what leafhopper or other vector transmitted it to the plant,” Dietrich said. “So the researchers must go back to the field to collect all possible insect vectors. Then they do transmission experiments, where they let leafhoppers feed on an infected plant and then put them on an uninfected plant so it can be seen.” whether it catches the disease or not.”

Because this research is laborious and slow, “we still don’t have a good idea of ​​which pests are spreading the most phytoplasm among plants,” Dietrich said. “It really limits your ability to establish an effective management strategy.”

For the new study, the researchers turned to leafhopper specimens in the INHS insect collection. Dietrich collected several of these insects as part of his work to classify their genetic relationship and evolution over a period of 25 years. Researchers examined 407 leafhopper species collected around the world in areas less disturbed by human development. Specimens came from North and South America, Africa, Europe, Asia and Australia.

The team extracted total DNA from the samples and processed each using both conventional and new sequencing approaches. The latter are less expensive and more informative than traditional methods, the researchers report. Of the sampled insects, 41 tested positive for phytoplasma, and the researchers obtained usable phytoplasma sequence data from 23 leafhoppers. Phytoplasms include those that cause a disease called aster yellowing, which inhibits photosynthesis and reduces the productivity of many different crop plants. These phytoplasma were found in several new species of leafhoppers that had never been previously identified as vectors of disease.

“These leafhoppers can transmit phytoplasma to wild plants in natural areas,” Trivelon said.

The study found phytoplasmas in areas of the world where such diseases had not been reported and identified several new strains of bacteria. It also found previously unproven associations between some phytoplasma and leafhopper species.

Scientists have no tools to target bacteria in asymptomatic plants to prevent disease outbreaks, so controlling phytoplasmas involves the use of insecticides to kill insect vectors.

“Since insecticides are only partially specific to the targeted insects, they also kill a variety of beneficial insects, which is not sustainable,” Trivelon said.

“We are finding that there are a lot of new phytoplasmas in nature that no one has ever seen before,” Dietrich said. “They do not cause disease symptoms in native plants to which they have probably been associated for millions of years. They only begin to cause disease when they jump to a new host that has not been exposed to phytoplasma before. “

Dietrich said the new findings parallel those seen in emerging infectious diseases of humans originating in wildlife. “That’s why we need to look more broadly into nature and see what’s out there.”

The National Science Foundation supports this research.

INHS is a division of the Prairie Research Institute at the University of Illinois at Urbana-Champaign.

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