Abstract

In Britain the raspberry suffers from some viruses that are soil-borne, others that are insect-borne, and still others whose mode of spread is unknown.
The soil-borne viruses - arabis mosaic, raspberry ringspot and tomato black ring - have ectoparasitic nematodes as vectors and are widely though locally distributed. Some varieties of raspberry are susceptible to one or more of them and develop severe stunting diseases, whereas others are immune from infection. Current knowledge of these viruses is briefly surveyed.
The aphid-borne viruses are mostly transmitted by Amphorophora rubi Kalt., and these divide into two groups, (a) heat labile and (b) heat stable, according to their ability to multiply in infected raspberry plants kept at 37 C. Viruses of group (a) cause necrosis in Rubus occidentalis and R. henryi and are sap-transmissible from R. occidentalis to non-Rubus hosts: they cause characteristic leaf symptoms in some raspberry varieties but vague or no leaf symptoms in others. The group probably comprises a number of similar viruses or virus strains. Group (b) includes Rubus yellow net virus, which, in conjunction with viruses of group (a), causes raspberry mosaic disease, and a number of ill-characterized viruses which cause leaf-yellowing diseases of raspberry. The viruses of both groups are of the non-persistent type; aphids acquire them in 1-2 hr. feeding on infected plants but retain infectivity for only 4-5 hr. Little is known of the vector relationships of vein chlorosis, a heat-stable virus transmissible by Aphis idaei v.d.G. but not by A. rubi. Raspberry varieties differ greatly in susceptibility to infection by these various viruses and some resist colonization by A. rubi.
Rubus stunt, a dwarfing disease of raspberry and other Rubus spp., occurs in southern England and in the Netherlands, where a leafhopper vector, Macropsis fuscula Zett., has been found. The virus seems to have a long latent period and to persist in its vector.
Diseases of which the etiology and mode of spread are still unknown include bushy dwarf, curly dwarf and yellow blotch. The first of these is associated with a sap-transmissible virus, the properties of which are described and which resemble those of tomato spotted wilt virus.