TABLE CONTENTS

Asymptomatic Carrier Trees in Pine Wilt Disease: From an Ecological
Viewpoint
Takeuchi, Y. & Futai, K.
Graduate School of Agriculture, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502,
Japan
The pine wood nematode (PWN; Bursaphelenchus xylophilus), the causal pathogen of pine
wilt disease, does not always kill the host pine due to the host-pathogen compatibility and
several biotic/abiotic factors including environmental conditions. The present study focused
on the asymptomatic host trees which show few, if any, symptoms even after infection with
the PWN, to enlighten their ecological importance.
Inoculation tests using susceptible host pine seedlings and an avirulent isolate of PWN
demonstrated that PWN could survive inside asymptomatic host seedlings without causing
any symptoms for long time. Secondly, as a possible positive effect of such latent infections,
it was investigated whether or not induced resistance due to PWN-infection could efficiently
protect the host. As a result induced resistance seemed to be effective only in delaying the
disease progress, but not in protecting the host for long periods.
To detect PWN inside host plant, a new method using molecular techniques was developed
and applied to intensive diagnosis in natural field sites. The results showed that many pine
trees in the field had been already infected even though some of them completely lacked any
typical symptoms such as dysfunction in resin secretion. Also, a mass emission of volatile
compounds, which should attract the vector beetles, from an asymptomatically infected pine
tree was detected in the natural pine stands. Thus, asymptomatic trees should be of ecological
importance since they may play a role as attractant of the beetles, PWN reservoir, and are
therefore an important factor in recurrence of pine wilt.
5 th International Congress of Nematology, 2008 59