VERTICILLIUM DISEASE OF STRAWBERRIES

Abstract

An intensive study was made of the morphology, cultural characters, and infection capabilities of 18 isolates of Verticillium. These were in part isolated from different Verticillium hosts occurring in the Niagara Peninsula and the balance were obtained as named stock cultures from different herbaria. In terms of their pathogenicity to strawberries, resistant and susceptible tomatoes, and eggplants, the isolates comprised a number of races whose virulence ranged from lethal to very mildly pathogenic. Under the experimental conditions, current-year runner plants of strawberries proved to be virtually immune from infection, in contrast to normal overwintered plants. The symptoms on the strawberry are variable and diagnosis should be confirmed by isolation of the pathogen, for which a technique was evolved. Morphologically the isolates varied considerably and in culture the color ranged from white through gradually deepening gray to black. At the extremes the differences were conspicuous but were so intergrading in the group as a whole that the isolates are regarded as belonging to one variable species which, because of priority, must be called Verticillium albo-atrum R. and B.