Monitoring of xylem embolism and dysfunction by the acoustic emission technique in Pinus thunbergii inoculated with the pine wood nematode Bursaphelenchus xylophilus |
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Authors: | Keiko Kuroda |
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Institution: | (1) Kansai Research Center, Forestry and Forest Products Research Institute, Momoyama, Fushimi Kyoto, 612-0855, Japan;(2) Present address: Laboratory of Forest Resources, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe 657-8501, Japan |
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Abstract: | Xylem dysfunction progresses rapidly in Pinus thunbergii infected with pine wilt disease. The present report deals with the timing and process of the extensive dehydration of tracheids
by embolism and the subsequent desiccation of the xylem with disease development. An ultrasonic acoustic emission (AE) technique
was used to detect embolisms in the xylem of pine trunks. In most of the P. thunbergii saplings inoculated with the pathogen Bursaphelenchus xylophilus, the AE frequency suddenly increased in the second week after inoculation. The high-frequency AE continued for about 3 days
and into the nights. Harvesting of specimens at this time revealed that white air-filled patches, representing the dehydrated
and dysfunctional areas, had just emerged in the sapwood. The AE events in the night must be due to something other than embolisms
in healthy trees. Frequent embolism of tracheids, which was suggested by the elevation of the AE frequency, might occur due
to the decrease in the tensile strength of xylem sap. This hypothesis is supported by previously reported data. Host cells
that had reacted to infection with B. xylophilus produce and release chemicals which can lower the surface tension of xylem sap. During the second increase of AEs, most of
which occurred in the third week, xylem desiccation and needle yellowing progressed. Needle fading then became distinct, and
the tree was close to death when the AE frequency dropped during the fourth week. By monitoring the AE, the first physiological
abnormality that took place very early after infection was detected. |
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