A host range survey of the M strain of plum pox virus in native Asteraceae weeds in Japanese apricot orchards and a possible infection cycle

Plum pox virus (PPV, genus Potyvirus) is one of the most economically important plant viruses. The PPV M strain (PPV-M) was first isolated in Japan in 2016. While a broad host range of the PPV M strain from trees to weeds has been widely reported, host range and the contribution of weeds to the PPV infection cycle in Japan remained unknown. In this study, we examined the host range of PPV-M in Japan within the Asteraceae weeds and explored its potential role as an intermediate host. By mechanically inoculating twelve herbaceous species belonging to Asteraceae (alternatively Compositae) in orchards with PPV-M, we found that all were susceptible to the virus. Of those, Hemisteptia lyrata showed high infection rates on the upper leaves, typically favored by aphids. A subsequent survey of multiple aphid species feeding on H. lyrata showed a seasonal infection cycle in which the aphid Aphis fabae solanella likely transmitted PPV-M from Japanese apricot leaves to H. lyrata in the spring. Then, A. spiraecola, an efficient PPV vector known to shift between hosts in summer and autumn, transmitted the disease to healthy Japanese apricot seedlings from PPV-M infected H. lyrata in autumn. It is conceivable that PPV-M in Japanese apricot orchards follows a seasonal infection cycle, potentially involving an intermediate host (Asteraceae) and two aphid species.