Bacteria Carried by the Pine Wood Nematode and Their Symbiotic Relationship with the Nematode
Although pine wilt disease was found in Japan in 1905 (Yano 1913), and has been studied for more than half a century, all the factors associated with the disease have not been clearly defined. For a long time it was thought that the pine wood nematode (PWN), Bursaphelenchus xylophilus was the only pathogenic agent causing the disease (Mamiya 1975d, 1983; Yang 2002). Subsequent studies found that toxins play an important role in the wilting process (Mamiya 1980; Bolla et al. 1982b; Oku 1988, 1990; Zhang et al. 1997) and that the PWN itself does not produce toxins (Cao 1997; Kawazu and Kaneko 1997). Oku et al. (1979) suggested that the production of toxins was associated with bacteria. It was also reported that bacteria exist in PWN-inoculated pine seedlings (Kusunoki 1987) and they were associated with the PWNs (Oku et al. 1979; Higgins et al. 1999). Using an electron microscope Zhao et al. (2000b) observed many bacteria adhering to the surface of the PWN’s body. The average number of bacteria carried by nematodes isolated from diseased trees was approximately 290 per adult nematode (Guo et al. 2002). Kawazu (1998) isolated three strains of bacteria that were toxic to both the callus and the seedlings of black pine. He also isolated the toxic substance and identified it as phenylacetic acid (Kawazu et al. 1996b; Kawazu 1998). Han isolated two species of bacteria from the nematode. Bioassay showed that the two species were strongly pathogenicity and possibly produced substances toxic to black pine seedlings and their callus (Han et al. 2003).
KeywordsSurface Coat Scanning Electron Micro Phenylacetic Acid Pine Wilt Disease Mutualistic Symbiosis
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