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Hamburg, Germany

Schmidt O.,University of Hamburg | Dujesiefken D.,Institute For Baumpflege | Stobbe H.,Institute For Baumpflege
Journal fur Kulturpflanzen | Year: 2014

Trees of about 5 years age of Aesculus hippocastanum L. were planted and infected with Pseudomonas syringae pv. aesculi, the causal agent of the Pseudomonas bark disease of horse chestnut trees. To get knowledge on the infection ways of the pathovar, trees were treated by complete spraying or by watering the root area with bacterial suspensions. In other trees bacteria from agar plate cultures were spread on the bark or the bacteria were brought in the wood through artificial bark wounds. One tree showed already after 3 months the typical dark bark leakages, confirming Koch's postulates. The other trees sampled after 3 years revealed that the pathovar could be re-isolated only from wound-infected trees and from two weakened or dead trees. Many of the wounds had been compartimentalized and/or totally over-walled, without a re-isolation of the bacterium. An infection via the leaves, the undamaged bark or the roots was not observed. It is assumed that P. syringae pv. aesculi infects A. hippocastanum through wounds.

Muller-Navarra A.,University of Hamburg | Gaiser O.,Institute For Baumpflege | Moreth U.,University of Hamburg | Dujesiefken D.,Institute For Baumpflege | Magel E.A.,University of Hamburg
Journal fur Kulturpflanzen | Year: 2014

A so far unknown disease which is found on red flowering horse chestnut (Aesculus × carnea Hayne) in the north-west of Germany has been investigated. It is characterized by the presence of fruiting bodies of Flammulina velutipes (Curtis) Singer and Pleurotus ostreatus (Jacq. ex Fr.) Kummer, able to cause breakage of branches and stems by white rot. Additional infection by Pseudomonas syringae pv. aesculi, and cracks of the bark are found.To get detailed knowledge of the disease, samples were taken from cross sections of four decayed red flowering horse chestnut stems. The investigation of individual tissues across the stem enables the assignment of the pathogens to the new disease. Sequencing of the rDNA-ITS identified F. velutipes and P. ostreatus, Bjerkandera adusta (Willd. ex Fr.) Karst. and Chondrostereum purpureum (Pers. ex Fr.) Pouzar, four white rot fungi, as main pathogens and some ascomycetes in the infected and decaying stem tissues.Our studies revealed the co-appearance of different basidiomycetes and ascomycetes in decaying tissue zones which emphasizes the complexity of the disease. It is also the first proof of involvement of F. velutipes as a parasite on red flowering horse chestnut. In addition, for the first time, Pseudomonas syringae pv. aesculi was detected in the inner bark and within the secondary xylem of natural infected red flowering horse chestnut. © 2014 Verlag Eugen Ulmer. All rights reserved.

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