IUFRO Working Party 7.02.02  FOLIAGE, SHOOT & STEM DISEASES
June 13-19, 2004, Oregon, USA
P.16

Magnetic Resonance imaging of xylem dysfunction in Quercus crispula infected with a wilt pathogen, Raffaelea quercivora

by K. KURODA1, Y. ICHIHARA2, Y. KANBARA3, T. INOUE4, and A. OGAWA4


1: Kansai Research Center, Forestry and Forest Products Research Institute
  Momoyama, Fushimi, Kyoto 612-0855, Japan
2: Tohoku Research Center, Forestry and Forest Products Research Institute
3: High Field Magnetic Resonance Imaging Research Institute, Iwate Medical University
4: Department of Neurosurgery, Iwate Medical University School of Medicine

Email: keiko@affrc.go.jp
http://cse.ffpri.affrc.go.jp/keiko/hp/kuroda-e.html

Summary

The large mortality rate of deciduous oaks, Quercus serrata and Q. crispula, has been a serious problem for the past two decades in Japan.  The pathogen of this wilt disease, Raffaelea quercivora, enters the trunks by mass attacks by an ambrosia beetle, Platypus quercivorus.  Physiological and cytological investigations of infected trees revealed that widespread discoloration and serious dysfunction had occurred in sapwood prior to the wilt.  The present report discusses the mechanism of wilting based on the non-destructive observation of xylem dysfunction using the MR imaging technique after the inoculation of three-year-old Q. crispula trees with the pathogen.  The MR imaging shows water-containing tissues as high intensity as a result of the behavior of proton.  Conductive vessels in healthy oak trees were recognized as whitish areas on the MR images.  By one week after the inoculation with R. quercivora, the area ca. 1cm above and below the inoculated sites showed low intensity and was looked darker.  Eight weeks after the inoculation, the area of low intensity had reached about 2cm above and below the infection site.  Anatomical observations after the MR imaging revealed that water conduction had stopped and there was desiccation in the darker areas.  T1 weighted images, which is used to detect the presence of fat or protein for medical purposes, showed the necrotic and discolored xylem area as high intensity.  Some substances produced by the activity of the pathogenic fungus might be detected on T1 weighted images.