Black raspberry necrosis (BRNV), raspberry leaf mottle (RLMV) and raspberry leaf spot (RLSV) are heat-labile viruses transmitted, probably in a semi-persistent manner, by species of Amphorophora. They are common in Europe and USSR and all Rubus species and hybrids tested can be infected by each of these viruses. Most plants are symptomlessly infected but each virus causes apical tip necrosis in R. henryi and R. occidentalis. Despite these similarities, the following features suggest that the viruses are distinct, though possibly related: (1) all red raspberry cvs experimentally infected with BRNV alone show no symptoms or only very faint chlorotic spotting, whereas pronounced angular chlorotic spotting of the leaves, and stunting, degeneration in vigour and sometimes death of plants occur in a few cvs that are sensitive to infection either with RLMV or with RLSV; (2) all three viruses frequently occur together in the same naturally infected plant; (3) BRNV but not RLMV or RLSV is mechanically transmissible to herbaceous test plants; (4) BRNV has particles c. 30 nm in diameter that can often be detected by electron microscopy of thin sections of infected leaves, whereas no such particles have been detected in sections of leaves infected with RLMV or RLSV; (5) the genetic bases for the reaction of red raspberry to infection with each of the three viruses are different.
Methods for detecting each of these viruses, the threat they pose to some red raspberry cultivars, and methods of preventing crop losses are discussed.