Electrical resistance properties of tree tissues in cankers incited by Endothiaparasitica and Nectriagalligena

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Abstract
Electrical resistance (ER) measurements were taken with a Shigometer across tree cankers found on Castaneadentata, Betulalenta, and B. populifolia. Cankers were incited by Endothiaparasitica and Nectriagalligena, respectively. Measurements taken along the vertical axis of the stem were at 2-cm intervals from 8 cm above the canker margin to 8 cm below the canker. Three zones of electrical character were distinguished. The canker margin exhibited decreased ER as compared with healthy tissue, whereas ER increased in the canker face. Moisture content, mobile cation concentration, and the path of current flow were all found to contribute to ER. Multiple regression analyses indicated fundamental changes in the variables contributing to ER in summer and winter samples. Strong inverse relationships were found between ER and total ash and between ER and potassium concentrations in September. February samples, however, exhibited an inverse correlation between ER and moisture content. These data indicated that moisture was the dominating factor in ER measurements of stem tissue in the winter.

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