Methods for isolating the alder Phytophthora

Phytophthora disease of alder (Alnus spp.) is now widespread in Europe. In France, difficulties were initially encountered in attempts to isolate the pathogen from necrotic bark tissue but, with experience, a high degree of success was achieved by direct plating onto agar media. Both corn meal agar and a selective medium derived from PARBHy were satisfactory. Success depended largely on the activity of the fungus in the bark tissue and some evidence was obtained that this varied from year to year. However, autumn was found to be a generally good period for isolation. It is possible to store collected samples at 7 +/- 4 degreesC for some days. The alder Phytophthora was isolated from the water of two rivers with a baiting method using alder twigs but the efficiency of the method was low.