Galling and reversion disease incidence in a range of blackcurrant genotypes, differing in resistance to the blackcurrant gall mite (Cecidophyopsis ribis) and blackcurrant reversion disease

An assessment was made of the response of 10 blackcurrant genotypes, differing in resistance to the agent of blackcurrant reversion disease (BRD) and to its gall mite vector, in field trials in Scotland and Finland over 5 yr. At each location, the 10 genotypes were planted in plots containing infector plants with high inoculum levels of the two organisms. In Scotland, the infector plants contained large numbers of gall mites (Cecidophyopsis ribis) and were infected with the European (E) form of BRD; in Finland, infector plants contained a different species of gall mite (C. spicata) and the severe Russian form (R) of BRD. As expected, at both sites, almost all plants of cvs Ben Alder, Ben Lomond, Ben Tirran, Ojebyn and an SCRI selection F4/1/66, which are susceptible to gall mite and BRD, became infested with each of these organisms. However, in Scotland but not in Finland, 58% of cv. Ojebyn plants were affected by BRD. The cv. Foxendown, which contains gene Ce that confers apparent immunity to C. ribis, was free from galls and failed to develop distinctive BRD symptoms at both sites. The cvs Rus and Neosypajuscajaija, which contain gene P which is reported to confer resistance to C. ribis, were infested more slowly by mites than the mite-susceptible genotypes and showed a smaller number of galls per plant. Also, they were infected with BRD more slowly than some mite-susceptible genotypes although by the end of the experiment, most plants were affected by BRD. All plants of cvs Golubka and Ben Gairn, which are resistant to the agent of BRD, remained free from distinct BRD symptoms at both sites despite the fact that plants contained galls. These data indicate the superiority of gene Ce over gene P for resistance to gall mites with the added benefit that the virtual immunity to gall mites provided by gene Ce provides a high level of protection against infection with BRD. The relative merits of these different forms of resistance to gall mites and BRD in blackcurrant are discussed in relation to present control methods for these two organisms and in the light of recent findings of different species of eriophyid mites on Ribes species.