The agent of raspberry yellows disease is transmitted by grafting but not by aphids and is resistant to thermotherapy. Further studies showed that it is transmitted by inoculation of sap through seed; it is probably transmitted to plants by pollination. RBDV shares all these attributes and is known to infect all yellows-sensitive raspberry cvs. except Puyallup and Sumner; however, neither of these cvs. has been tested by graft inoculation with RBDV. RBDV commonly infects plants symptomlessly, even those of yellows-sensitive cvs., but it induced yellows when inoculated either manually to Norfolk Giant raspberry or by grafting to a yellows-sensitive raspberry selection. The evidence suggests that RBDV causes yellows disease but that symptom expression is greatly dependent on genetic and environmental factors. Many red raspberry cvs. are resistant, probably immune, to the type culture of RBDV. This character was shown to be conferred by a single dominant gene designated Bu.