Abstract

An experiment is described in which an attempt was made to classify 10 seedling derivatives of the raspberry variety Malling Exploit, 17 seedling derivatives of Norfolk Giant, 8 named varieties and 3 other seedling selections for resistance to both mosaic disease and colonization by the aphid vector Amphorophora rubi Kalt. The Malling Exploit derivatives appeared to be segregating for resistance to the virus but showed little or no evidence of aphid resistance. On the other hand Norfolk Giant and its progeny all showed good disease resistance, of which weak to moderate aphid resistance appeared to be a component in the parent and some of the derivatives. Data are presented on the inheritance of this weak aphid resistance, but both its mode of inheritance and its significance as a factor influencing virus escape remain uncertain. It is concluded that the strong aphid resistance shown by Malling Landmark (gene A₁ provided good protection against virus spread, but that this protection could be enhanced by combining it with resistance to the viruses themselves. Virus resistance would provide additional protection against infection by itinerant aphids and also act as an insurance against the advent of new aphid strains. The form of virus resistance present in Norfolk Giant seems to be the one required, since it may be of a ‘general’ type. Present methods of testing for virus resistance are either laborious or inefficient, however, and it is suggested that improvements may be possible with greater understanding of host-virus interactions in infected plants of resistant and susceptible varieties.