Characterization and serological detection of four closterovirus-like particles associated with leafroll disease on grapevine

Four serologically unrelated closterovirus-like particles (GLRV-1, GLRV-2, GLRV-3 and GLRV-4) were isolated in our laboratory from leafroll diseased grapevines. Polyclonal antibodies raised against these particles were useful for their characterization and their detection in infected plants. The coat proteins of these four serotypes were characterized by a SDS-PAGE after denaturation, followed by a transfer on nitrocellulose sheet and immunoprinting using the specific polyclonal antibodies. The capsid of GLRV-1, GLRV-2, GLRV-3 and GLRV-4 contains a single protein species with molecular weight of about 39 Kd, 26 Kd, 43 Kd and 36 Kd respectively. No serological relation was found between these four filamentous particles either by ELISA, immuno electron microscopy or immunoblotting experiments. Serological analysis of many grapevines originating from the Middle East and Europe showed a very close association between the presence of GLRV-1, GLRV-2, GLRV-3 and GLRV-4 antigens, and leafroll symptoms on Vitis vinifera Pinot Noir. This association was confirmed by testing symptomless and diseased grapevines collected in the field, and by serological analysis of heat treated plants originally infected by GLRV-1 and GLRV-3, which are the most widespread antigens detected in leafroll infected grapevines.