Verticillium dahliae is a major threat to the cultivation of lilac cut flowers in the Netherlands. To reduce losses due to Verticillium five less susceptible rootstocks to Verticillium were selected.
Three of the five could be succesfully propagated in tissue culture. Lilac shrubs were cultivated on these three rootstocks and forced to flower at high temperature in a greenhouse. One of the rootstocks gave very good results; shrubs cultivated on this rootstock were the most vigorous and production was higher than on traditional seedling rootstocks. No visible symptoms of Verticillium were detected during the cultivation. In adjacent plants on traditional seedling rootstock, wilting symptoms as a result of Verticillium were detected. This shows that plants grown on selected rootstocks are less susceptible to Verticillium than plants on traditional rootstocks. The selected rootstocks are not resistant, as Verticillium was detected in a poorly growing shrub grown on a selected rootstock. Wilting symptoms and Verticillium were also detected in young ugrafted rootstocks planted on a heavily infested field. This research is conducted by Wageningen UR Greenhouse Horticulture in close cooperation with lilac cut flower growers and financed by the Dutch Product Board of Horticulture.