Distribution and Frequency of Little Cherry Virus 2 Genotypes in both Production and Ornamental Fruit Trees in the Pacific Northwest

Authors: SHIRES, MADALYN - South Dakota State University; MOLNAR, CODY - Washington State University; Wright, Alice; BISHOP, GARRETT - Gs Long Company; HARPER, SCOTT - Washington State University

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2023
Publication Date: 3/8/2024
Citation: Shires, M.K., Molnar, C., Wright, A.A., Bishop, G., Harper, S.J. 2024. Distribution and Frequency of Little Cherry Virus 2 Genotypes in both Production and Ornamental Fruit Trees in the Pacific Northwest. Plant Health Progress. https://doi.org/10.1094/PHP-09-23-0077-S.
DOI: https://doi.org/10.1094/PHP-09-23-0077-S

Interpretive Summary: Little cherry virus 2 (LChV2) causes little cherry disease, a problem in cherry orchards the U.S. Pacific Northwest (PNW). There are two genotypes (LC5 and Rube-74) of LChV2 in Washington. Here we used data and samples from 2017-2022 to determine the incidence of each genotype in the PNW, their distribution in cultivated vs. ornamental trees, and co-infection of both genotypes in trees. We found that there was no pattern in Washington as both genotypes are present throughout the state. In Oregon LChV2 positives were mostly in one region. In both states, LC5 was the most common and widespread. This suggests that the Rube-74-like isolates found are more recently introduced but are being actively spread. Both LC5 and Rube-74 were found in cultivated and ornamental trees. Co-infection of a single plant by both LC5 and Rube-74 was common in both states. LChV2 titer and frequency did decrease in the presence of ‘Candidatus Phytoplasma pruni’. These data will help us better understand the biology of this virus in the PNW.

Technical Abstract: Little cherry virus 2 (LChV2) is the causal agent of little cherry disease, a recurring problem affecting cherry production the U.S. Pacific Northwest. Previous research has shown that there are two genotypes (LC5 and Rube-74) of LChV2 present in Washington. Here we used data and samples from 2017-2022 to determine the incidence of each genotype in the PNW, their distribution in cultivated vs. ornamental host systems, and for evidence of co-infection of both genotypes in individual plants. We found that there was no geographic pattern in Washington, as both genotypes are distributed throughout the state, while in Oregon LChV2 postives were concentrated on one region. In both states, the LC5 genotype was the most common and widespread of the two genotypes, suggesting the Rube-74-like isolates found are more recently introduced, but are being actively transmitted. There were no host-specific patterns found as both genotypes were found in cultivated and ornamental cultivars. Co-infection of a single plant by both genotypes was common in both states, with no evidence of superinfection-exclusion, although interestingly, LChV2 titer and frequency decreased in the presence of ‘Candidatus Phytoplasma pruni’. Cumulatively, these data will help us better understand the epidemiology of this pathogen in the Pacific Northwest.