Distribution and frequency of little cherry virus 2 genotypes in both production and ornamental fruit trees in the Pacific Northwest

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 positives 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.