PATHOGENICITY TESTS WITH BURSAPHELENCHUS- MUCRONATUS ON PINE AND SPRUCE SEEDLINGS IN GERMANY

Inoculation tests on Pinus sylvestris seedlings with a German, a Siber ian and a French isolate of Bursaphelenchus mucronatus and on Picea ab ies seedlings using only the German isolate have clearly shown, under German field conditions, that the nematode can cause wilt symptoms on the apex of about 60% of the inoculated P. sylvestris plants. The nema todes in all these tests mostly remained near the inoculation sire. Ho wever, further spread of the nematodes and wilt symptoms occured when a climate chamber, at 25 degrees C, was used or when the French isolat e was used outdoors. At 25 degrees C, 10% of the inoculated plants wit h at least 1000 nematodes per seedling died. Seedlings' apices wilted if more than 50 nematodes per trunk were present, whereas smaller numb ers of nematodes could cause partial wilting. Nevertheless, a few pine seedlings did tolerate high nematode-population densities, up to 966 per plant. No further progress of wilt of plants with symptoms was obs erved the following year. Inoculations of P. abies with a German isola te resulted in population development near the sire of inoculation. Sp ruces largely tolerated nematode infestations without any development of wilt symptoms.