Alternative hosts of ‘Candidatus Phytoplasma pruni’ identified through surveys and vector gut content analysis

Authors: SHIRES, MADALYN - South Dakota State University; MOLNAR, CODY - Washington State University; COWELL, SARAH J - Washington State University; BISHOP, GARRETT - Gs Long Company; VOELKER, JENNA - Gs Long Company; THOMPSON, ASHLEY - Oregon State University; NIKOLAEVA, EKATERINA - Pennsylvania Department Of Agriculture; COPP, CODY - Oregon State University; FLANDERMEYER, LAURA - Washington State University; MELTON, TAWNEE - Washington State University; NORTHFIELD, TOBIN - Washington State University; Marshall, Adrian; Cooper, William; HARPER, SCOTT - Washington State University

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2025
Publication Date: 1/14/2025
Citation: Shires, M.K., Molnar, C., Cowell, S., Bishop, G., Voelker, J., Thompson, A.T., Nikolaeva, E.V., Copp, C., Flandermeyer, L., Melton, T., Northfield, T.D., Marshall, A.T., Cooper, W.R., Harper, S.J. 2025. Alternative hosts of ‘Candidatus Phytoplasma pruni’ identified through surveys and vector gut content analysis. Plant Health Progress. https://doi.org/10.1094/PHP-09-24-0089-RS.
DOI: https://doi.org/10.1094/PHP-09-24-0089-RS

Interpretive Summary: X-disease causes substantial economic losses for cherry and stone fruit growers in the Pacific Northwest. This disease is caused by the bacterium Phytoplasma pruni spread by leafhopper vectors, but information about which plant species serve as sources of infected leafhoppers in orchards complicates X-disease management. Researchers at the USDA-ARS in Wapato, Washington collaborated with scientists at Washington State University to survey weeds in and around orchards for presence of Phytoplasma pruni. They detected the pathogen in 21 species of common broadleaf weeds. Using molecular gut content analysis, the researchers found that leafhoppers routinely fed upon the majority of the Phytoplasma hosts. These results show that broadleaf weeds are important sources of Phytoplasma-infected leafhoppers in cherry and stone fruits, and that management of these weeds in orchards can reduce the risk of X-disease outbreaks.

Technical Abstract: An ongoing outbreak of X-Disease, caused by ‘Candidatus Phytoplasma pruni’ has resulted in severe economic losses for cherry and stone fruit growers in the U.S. Pacific Northwest in the last decade. Given that this pathogen is transmitted by polyphagous leafhopper species, primarily Colladonus montanus reductus and C. geminatus in the PNW, alternative hosts present a significant management concern. Here we surveyed phytoplasma incidence in non-Prunus plants found in and around stone fruit orchard borders, and compared these results to the leafhopper feeding patterns through gut content analysis. We confirmed that ‘Ca. P. pruni’ infection in 21 plant species from 15 families. Of these, 15 species were commonly found in the diets of phytoplasma-carrying leafhoppers. Due to the abundance of common species, including Taraxacum, Malva, and Trifolium spp., alternative hosts were found across all growing seasons, although ‘Ca. P. pruni’ titer was low (<102 cells) in most of these hosts. No geographic patterns were identified, instead phytoplasma incidence and spread at individual orchards was related to the management of annual and biennial host species, thus removing preferred leafhopper feeding hosts. These data suggest alternative host removal, along with removal of infected trees, is an effective means of slowing disease spread.