BRNV induces a severe apical necrosis in black raspberry (Rubus occidentalis) but shows no diagnostic symptoms in red raspberry. However, infection of F1, F2 and F3 hybrids from the cross black raspberry X red raspberry induced mosaic symptoms of varying intensity but no typical apical necrosis.
In a survey of 28 red raspberry cvs. a few developed severe angular chlorotic leaf spots when infected with RLMV, and a few others did so when infected with RLSV. These reactions were determined by single dominant genes designated Lm and Ls, respectively.
The value of the different host reactions for controlling the effects and spread of these viruses is discussed.