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Use of Magnetic Resonance Microscopy for the Nondestructive Observation of Xylem Cavitation Caused by Pine Wilt Disease

First author: Institute of Applied Physics, University of Tsukuba, Ibaraki, Japan and MR Technology, Inc., Tsukuba, Japan; second author: Laboratory of Biosphere Functions, Institute of Environmental Studies, Graduate School of Frontier Sciences, the University of Tokyo, 113-8657, Japan; and third author: Experimental Station at Tanashi, University Forests, the University of Tokyo, Japan

The development of xylem cavitation caused by pine wilt disease was visualized nondestructively with a compact magnetic resonance (MR) microscope system. A T₁-weighted spin-echo sequence clearly visualized the water-filled xylem of Japanese black pine (Pinus thunbergii) as white zones, whereas cavitated xylem was represented as dark areas. Cavitated areas in the xylem were first observed 6 to 9 days after inoculation with the pinewood nematode (Bursaphelenchus xylophilus), and enlarged gradually over several days. After 11 to 18 days, cavitated areas rapidly increased in size, fused, and reached the cambium. This drastic expansion in cavitation coincided with and appeared to explain the sudden wilting of the seedlings. The development of cavitation observed through MR microscopy corresponded well with previous descriptions of disease progression.

Additional keywords: embolism , magnetic resonance imaging , water transport .