Kuroda, Keiko

Anatomical and noninvasive techniques to detect the first internal symptom in diseased trees

Anatomy is a fundamental procedure to reveal the mechanism of symptom development in the trees infected with pathogens. Anatomical data, however, had been an appendix for long years in the forest pathology in which mycological investigation has priority. To find internal phenomena that induce symptoms, it is very important to observe the plant tissue from the very early period of infection when the external symptoms have not initiated, and periodical sampling thereafter is necessary to follow the changes. Anatomy in the later period when tissues were dead and degraded by microorganisms does not provide useful information. The concept of functional anatomy is especially important in the pathological researches. The defense reaction in the host tissue against the pathogen decides the fate of the tree, that is, the mortality or survival. In the pathological anatomy, there is a strong interest in achieving noninvasive investigations on living trees. Repeated analysis on the same tree has been difficult due to the requirement of destructive observations. As a noninvasive technique, magnetic resonance imaging is increasingly used on plants. Detectable incidences by MR imaging and the image qualities vary with the combination of parameters during scanning. The parameters to obtain images suitable for physiological and pathological studies of trees have been improved. The distribution of water is detectable in the tissue by proton density spin-echo sequences, and anomalies in diseased tissue are detectable by the T1 weighted sequences. MR images clearly showed the enlargement of dysfunctional area in the sapwood of Quercus crispula that was inoculated with a wilt pathogen, Raffaelea quercivora. The acoustic emission technique that detects embolism in water conduits of trees also is a noninvasive technique helpful to find abrupt xylem dysfunction in some wilt diseases. These noninvasive techniques are providing new information and helping the development of tree pathology.