Blackberry Leaf Blotch Virus, a Novel Emaravirus Infecting Cultivated and Wild Blackberry Plants in Europe

A novel emaravirus provisionally named blackberry leaf blotch virus (BLBV), was identified from cultivated and wild blackberry plants ( Rubus sp.) exhibiting leaf blotch and vein banding/feathering symptoms. BLBV has been detected in Belgium, France, the Netherlands and Slovenia. The virus is most closely related to raspberry leaf blotch virus (RLBV, Emaravirus idaeobati ) infecting raspberry ( Rubus idaeus ) in Europe, and is distant from blackberry leaf mottle-associated virus (BLMaV, Emaravirus rubi ), infecting blackberry in the USA. Up to eight RNA segments were identified in BLBV isolates, including the four core RNA segments present in all emaraviruses and up to four additional non-core RNA segments. Spherical virus-like particles (70-90 nm), morphologically similar to emaravirus virions, were observed in sap from symptomatic blackberry tissue by transmission electron microscopy. The proteins encoded by the core RNA segments were all more than 20% divergent from their closest known emaravirus homologues, supporting the classification of BLBV as a new species. Genetic diversity was found among isolates even at the country level, with some additional RNA segments only detected for some isolates. Eriophyoid mites, known vectors of emaraviruses, were found on several infected plants and molecular barcoding identified the them as Epitrimerus gibbosus , an eriophyoid species previously reported on Rubus spp. in Europe. Transmission bioassays performed with these mites in a greenhouse supported E. gibbosus as a putative vector of BLBV. This discovery raises questions about the impact of BLBV on blackberry crops and the need for virus surveillance in plant propagation material.