Discovery of Phytophthora ramorum on Rhododendron sp. in France and Experimental Symptoms on Quercus robur
Claude Delatour1, Carole Saurat2, Claude Husson3, Renaud Ioos4 and Nathalie Schenck2
The first evidence of Phytophthora ramorum in France was found in several garden centres on Rhododendron sp. in April 2002. Brown spots on leaves, buds and twigs necrosis were observed. During 2002, the unit of Mycology of the French Plant Protection Service carried on a national survey in nurseries. About 300 samples were analysed by isolation on a Phytophthora selective medium. Species identification was based on morphological characterisation. P. ramorum was detected in 68 samples (63 from Rhododendron and 5 from Viburnum spp.) originating from several geographical areas covering the entire french territory.
Concerning the experimental symptoms, saplings and seedlings of Quercus robur were inoculated with a French isolate. Two types of inoculation were performed : by inserting mycelium on bark wounds and by spraying sporocysts. All the inoculated cuttings produced bark necrosis with occasional dark bleeding. The length of necrosis on the stem ranged from 1.4 to 8.3 cm. These results are similar to those obtained on tanoak and coast live oaks (Rizzo et al, 2002) but we observed no girdling, no wilting and no death on Q. robur even 40 days after inoculation. With respect to the damage on leaves, necrosis was not frequent. Therefore, Q. robur seems to be less susceptible than Q. agrifolia and Lithocarpus densiflorus. In addition, our results suggest that bark necrosis, dark bleeding and occasionally leaf necrosis are good candidate symptoms of P. ramorum for future forest surveys.
1INRA, Unit of Forest Pathology, 54280 Champenoux, Nancy, France
2LNPV, Unit of Mycology, 54000 Nancy, France
3INRA, Unit of Forest Pathology, 54280 Champenoux, Nancy, France; claude.husson@nancy.inra.fr
4LNPV, Unit of Mycology, 54000 Nancy, France; renaud.ioos@agriculture.gouv.fr
|
