FURTHER INVESTIGATIONS OF THE BLACK-CURRANT REVERSION DISEASE IN NEW-ZEALAND

An evaluation of several black currant (Ribes nigrum L.) cultivars rec ommended or suggested as indicators for the reversion disease, showed 'Baldwin' to be the most sensitive. 'Kentish Hero' and 'Silvergieters Schwarze' were almost as sensitive as 'Baldwin', but 'Ojebyn' did not express definitive symptoms. A virulent strain of reversion found in t he cultivar 'Kentish Hero' appears similar to the V-1 strain reported in England. Moderate, and possibly mild, strains occurred in several o ther cultivars. However, the severe ''R'' form of the disease causing the split sepal symptom of black currants in Scandinavia and Eastern E urope does not appear to be present in New Zealand. Surveys in 1990, 1 991, and 1996 of commercial properties growing black currants in the S outh Island showed that reversion was present in several plantings in South Canterbury and Otago, and was widespread in Southland plantings. A low incidence of reversion in Nelson is thought to have been elimin ated by the removal of infected plants. North Canterbury plantings rem ain free from infection, but infection has appeared at two locations i n mid Canterbury. Spread of infection between properties was initially caused through the inadvertent use of infected propagation material, and further spread within properties by the gall mite (Cecidophyopis r ibis Westw.) vector. The use of gall mite resistant cultivars appears to be the only effective means for the control of reversion.