Pathogenesis of Pear Chlorotic Leaf Spot-Associated Virus and Its Transmissibility by an Eriophyid Mite Species

Pear chlorotic leaf spot-associated virus (PCLSaV) is a fimovirus infecting Asian and European pears that is endemic to China and Japan. Disease symptoms, including chlorotic leaf spot (CLS), leaf necrosis, and bark necrosis, can be observed on PCLSaV-infected pear trees and can result in considerable loss of quality and yield. However, the causal relationship between these symptoms and PCLSaV infection remains poorly understood. Furthermore, although some fimoviruses can be transmitted by mite species of the family Eriophyidae, to date no vector mite species for PCLSaV have yet been identified. Since PCLSaV disease frequently co-occurs with Japanese pear rust mite (JPRM; Eriophyes chibaensis Kadono; Acari: Eriophyidae) infestation, we performed transmission experiments that examined the spread of PCLSaV from infected to healthy pear seedlings via JPRMs. Inoculation with PCLSaV-viruliferous mites onto healthy pear seedlings resulted in infection of PCLSaV and the reproduction of CLS symptoms and bark necrosis, while inoculation by nonviruliferous mites did not. No evidence of transovarial transmission was observed. Finally, we propose renaming the virus as pear chlorotic leaf spot virus since Koch's postulates for the CLS symptoms/PCLSaV infection are fulfilled.