Migration of the pinewood nematode, Bursaphelenchus xylophilus, to the mycelia of wood-decay fungi was investigated on water agar plates. A very strong ability to attract nematodes was shown by Pleurotus ostreatus, P. pulmonarius, P. eryngi, Lentinula edodes and Lampteromyces japonicus, all of which had been demonstrated to be nematophagous in previous studies. Other wood-decay fungi, Neolentinus lepideus, Trichaptum abietinum, Cryptoporus volvatus and Pholiota nameko, having less or no ability of killing nematodes, did not attract nematodes. Botrytis cinerea attracted nematodes although not as strongly as the nemtophagous wood-decay fungi. Based on the experimental results it could be concluded that nematophagous wood-decay fungi were attractive to the pinewood nematode.

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DNA sequences of the internal transcribed spacer (ITS) region of the nuclear rRNA gene and mitochondrial cytochrome oxidase I (COI) gene were used to analyze intraspecific variations and infer phylogenetic relationships of steinernematids isolated from Japan. DNA fragment lengths of the amplified ITS region obtained from 19 Japanese steinernematid isolates ranged from 914-1,067 bp and varied considerably among the species. A few intraspecific variations were detected in Steinernema litorale, Steinernema spp. MY6 and MY8, and no variation was observed in S. monticolum and Steinernema sp. MY5 in the sequences of the ITS region. The fragment length of the amplified partial COI gene was 397 bp for all species. The intraspecific variations of the sequences ranged from 0.3%-7.8% (0-42 nucleotide differences) for S. monticolum, S. litorale, Steinernema spp. MY5, MY6, and MY8. Sequence comparisons and phylogenetic analyses reveal that the sequence of the COI region can distinguish the isolates within a species but is not as effective as the ITS region in elucidating the relationship among species.

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The native Japanese pines Pinus thunbergii and P. densiflora are susceptible to pine wilt disease caused by the pinewood nematode, Bursaphelenchus xylophilus, while P. taeda is more resistant than these native Japanese species. We studied symptom development in these three pines after inoculation with a virulent isolate of the pinewood nematode. Nematode populations increased throughout seedlings of both P. thunbergii and P. densiflora soon after ray parenchyma cells showed drastic histochemical changes, i.e. accumulation of catechol tannin, spread of lipids over the whole cell, and leakage of cell contents. However, in P. taeda seedlings, nematode populations remained low and histological changes occurred only near the inoculation site. These results suggest that drastic cytological changes in ray parenchyma cells may promote symptom development from an early to an advanced stage.

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