Nematological Research (Japanese Journal of Nematology)

The phylogenetic relationships of ten Japanese steinernematid species and their symbiotic Xenorhabdus bacteria were analyzed. Based on the sequences of the ITS region of the rRNA gene, Japanese steinernematids were categorized into three clades: ‘affine-intermedium’ including Steinernema sp. MY7; “karii-glaseri” including Steinernema sp. MY8; and “monticolum-kushidai-feltiae-kraussei” including Steinernema sp. MY5, S. monticolum, S. kushidai, S. litorale, S. feltiae, Steinernema sp. MY3, Steinernema sp. MY6, and S. kraussei. In the phylogenetic analysis of the 16S rRNA gene of their symbiotic Xenorhabdus bacteria, six out of ten Xenorhabdus bacteria isolated from Japanese steinernematids formed a cluster with X. bovienii, but the other four bacteria isolated from Steinernema sp. MY8, S. kushidai, S. monticolum and Steinernema sp. MY5 did not. The phylogenies of the nematodes and their associating bacteria were partially related to each other, with a few exceptions.

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The seasonal changes in the number of free-living nematodes and the pinewood nematode (PWN), Bursaphelenchus xylophilus, in 15-year-old Japanese black pine (Pinus thunbergii) trees killed by the PWN were determined. Fifteen species of nematodes were isolated, i.e. one species, each of Mononchida and Plectidae, two species, each of Monhisterida, Rhabditida and Tylenchida, three species of Bursaphelenchus including the PWN, and four species of Diplogasterida. The PWN and one species of Diplogasterida were the most prevalent nematodes isolated. The numbers of PWNs decreased from August to December, 2004, but then increased in February, 2005, then decreased again until June, 2005. During the experimental period the population changes of the Diplogasterida nematode mimicked those of the PWN, however, correlations between the numbers of the two nematodes varied considerably both among trees and seasons. Both the PWN and the Diplogasterida nematode were more abundant around the pupal chambers of the vector beetle, Monochamus alternatus, than elsewhere in the tree wood.

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