AN ASSESSMENT OF THE PATHOGENICITY OF THE PINE WOOD NEMATODE, BURSAPHELENCHUS XYLOPHILUS, IN THE NORTH CENTRAL UNITED STATES (APHELENCHOIDIDAE, PINUS SYLVESTRIS, PINUS RESINOSA)

The pathogenicity of Bursaphelenchus xylophilus was examined through inoculation studies of established trees in the field. Wounds produced on four branches in single whorls on Scots, jack, and red pine trees were inoculated with 10,000 nematodes each. After 14 weeks, 34 and 27 percent of the inoculated branches on the Scots and jack pines were dead or dying above the inoculation sites, respectively. No symptoms occurred on inoculated red pine trees or on any of the controls. Nematodes inhibited wound closure and branch death was attributed to the formation of girdling cankers at the inoculation sites.;Scots pine trees were inoculated with B. xylophilus using two techniques in southeastern Iowa to determine if results from previous studies in Minnesota and Wisconsin could be extrapolated over a broader geographic area. Four months after inoculation 50 percent of the inoculated trees were dead or dying. None of the control trees had symptoms. An average of 393.1 nematodes per gram of wood were extracted from inoculated branches. Nine of 10 inoculated trees sampled at 4 months contained nematodes in the main stems. An average of 329.9 nematodes per gram of wood were extracted from samples collected from the trees which had been inoculated through drill wounds to the main stems.;Results presented document B. xylophilus as a primary cause of tree death under certain conditions. Further investigations are needed to explain the observed differences between the pathogenicity studies presented and to elucidate the conditions necessary for disease development.;To determine the effects of inoculation date on nematode infection and to further document the formation of branch cankers, Scots pine trees were inoculated with B. xylophilus on different dates. Inoculation date had no significant effect (P < 0.05) on wound closure or the average number of nematodes extracted from inoculated branches. The average differences in length and width of wound closure between treatments for the three inoculation dates were -6.6 cm and -1.9 cm, respectively. An average of 68.7 nematodes per gram of wood were extracted from inoculated branches. No nematodes were extracted from samples collected from the main stems of inoculated trees.