Zu den Ausbreitungswegen von Phytophthora ramorum an Rhododendron und Viburnum auf Container-Stellflächen

In Europe, Phytophthora ramorum basically infects Rhododendron and Viburnum. To prevent the spread of the new quarantine organism in nurseries more knowledge about the transmission biology of this pathogen is necessary. For this reason the pathways of spread for P. ramorum on the two main host plants have been studied for the first time. Under practical field conditions inoculated plants were placed as sources of infections in a larger stock. Over 3?months the development of infestation was recorded. The pathogen showed a poor potential of spread. At the end of the trial only 1.0% of Rhododendron and 0.3% of Viburnum were infested with P. ramorum. Typical symptoms could be observed. On Rhododendron the pathogen caused a branch dieback. Stems showed a brown discoloration, which starts usually at the tip of the twig and moved towards the base. Infected Viburnum showed a stem base rot with wilting symptoms. Additionally rhododendrons were natural infested with Phytophthora citricola. This pathogen caused the same symptoms like P. ramorum and spread much faster. Investigations of leaf litter showed that both Phytophthora species had colonized the ground. This observation and the pattern of spread indicate that inoculum on the ground has been transmitted to arial plant parts via rainsplash. There is little evidence that P. ramorum has been transmitted directly from plant to plant via splashwater or air.