Beet soil-borne virus (BSBV) is a Pomovirus transmitted to Chenopodiaceae by the protist Polymyxa betae , which is also the vector of the etiological agent of the rhizomania syndrome of sugar beet, the Beet necrotic yellow vein virus (BNYVV). Originally reported in Italy, rhizomania disease is now widespread in most countries where sugar be et is grown and BSBV is often found in beet infected by BNYVV. However, the pathogenicity of BSBV and its contribution to the rhizomania syndrome remain unclear, with opinions still divi ded on the matter. For a better understanding of the functionality and pathogen icity of BSBV, full-length cDNA clones have been constructed for the three genomic RNAs. With the aim of assessing thei r effectiveness and relative contribution to the virus house-keeping functions, transcripts were inoculated on Chenopodium quinoa and Beta macrocarpa leaves using five genome combinations. Both RNAs-1 (putative replicase) and -3 (putative movement proteins) proved to be essential for virus replication in planta and symptom production on C. quinoa , whereas RNA-2 (putative coat protein, CP, and a read-through domain, RT) was not. No symptoms were recorded on B. macrocarpa , but viral RNAs were detected. In both host plants, the 19 kDa CP was detected by western blotting as well as a 115 kDa protein corresponding to the CP-RT. Our study describing the first infec tious full-length cDNA clone available for a beet Pomovirus provides therefore a useful tool for further investigating the pathogenicity of BSBV in the complex rhizomania syndrome, as well as its replic ation and infection mechanisms, and the potential viral interactions with other beny- and pomovi ruses on both susceptible and rhizomania-resistant beets.

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