Serological and molecular evidences that croton vein yellowing nucleorhabdovirus is an isolate of eggplant mottled dwarf virus

In the Spring of 1990, Croton vein yellowing nucleorhabdovirus (CVYV) was found for the first time in some dwarfed plants of croton (Codiaeum variegatum L.) “Fred Sander” showing malformation and yellow or pink veins. CVYV was mechanically transmitted to Nicotiana glutinosa and Chenopodium amaranticolor and, by leaf-graft, to healthy croton plants in which it induced the same original disease. After about twenty years from the first finding, CVYV has been serologically identified and molecularly characterized as an isolate of Eggplant mottled dwarf virus (EMDV). In electron microscopy of negatively stained crude extracts from croton, fixed in gluteraldeid solution, typical bacilliform virus particles were observed; by applying immunoelectron microscopy tests, using an antiserum to an EMDV Iranian potato isolate, all these particles were clearly decorated. EMDV was also detected in original croton by DAS-ELISA (Bioreba kit; Switzerland) and by RT-PCR using a virus-specific primer pair designed to amplify ca. 900 bp fragment of the P1 polymerase gene. The amplicon was cloned and sequenced at MWG (Ebersberg, Germany) on both strands. Sequence obtained showed 86.5% identity with EMDV eggplant isolate from Greece, confirming the identity of rhabdovirus infecting symptomatic croton. From this serological and molecular study, it appears evident that CVYV can be definitively considered an isolate of EMDV. In the last decade, EMDV has been frequently detected infecting two common ornamental species in Mediterranean area, Hibiscus rosa-sinensis and Pittosporum tobira. From this study croton, typical pot-houseplant appreciated for its large and glossy leaves, can be considered a new natural host of EMDV.