Inoculation of Pine Trees with Avirulent Pinewood Nematode Under Experimental Conditions: Risk-Benefit Analysis
Virulence of the pinewood nematode, Bursaphelenchus xylophilus, varies widely from highly virulent to avirulent, or less pathogenic. The inoculation of pine trees with avirulent B. xylophilus induces resistance to subsequently inoculated virulent B. xylophilus. This induced resistance may constitute a biological control strategy for pine wilt disease. The characteristics of induced resistance have been previously identified in short-term experiments. In this study, the long-term and yearly repeated experiments were conducted to further understand the nature of induced resistance and the potential for control measures. Induced resistance of pine trees by avirulent B. xylophilus was re-confirmed, although the effects were not as strong as trunk injection with nematicides. The avirulent B. xylophilus remained avirulent in the long term, but occasionally caused tree mortality. The results show that the benefit, i.e., the chance of tree survival, outweighed the risk of tree mortality by avirulent B. xylophilus when pine trees were subsequently inoculated with virulent B. xylophilus. Explorative use of this resistance-inducing method will be possible in areas where pine wilt disease occurs naturally. More study is necessary to determine the effect of induced resistance against natural infection with B. xylophilus from vector insects.
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