No abstract

Leaf mesophyll protoplasts and cell suspension cultures obtained from resistant and susceptible cultivars of hop (Humulus lupulus) exhibited differential cell death responses when treated with sterile culture filtrates (CF) obtained from four isolates of Verticillium albo‐atrum showing a range of virulence towards hop. The extent of cytotoxicity was correlated with both the virulence of the isolates and the resistance of the cultivars. Cytotoxicity was attributed to a low‐molecular‐weight, heat‐labile, component of CF. Cell cultures from a susceptible and a resistant cultivar exhibited similar, growth‐related, patterns of sensitivity to CF. The extent of inhibition of callus growth caused by CF treatment was related to the level of the resistance of the cultivar.