Abstract
In a pear orchard located near a iodine refinery, severe damages were observed on the pear leaves. We have investigated the possible cause of the damages. The results of field surveys are as follows:
1) The leaf damages were interveinal or leaf-margin necrosis, the former symptom was found in the cultivars Kosui and Shinsui, while the latter was in Yagimi and Hakko. In the case of severe damages pear leaves fell down early.
2) The extents of leaf damages differed depending on the pear cultivars; Kosui and Hakko were sensitive, Chojuro was resistant, and Shinsui and Yagimi were intermediate.
3) The concentrations of iodine, chlorine, sulfur, bromine and fluorine were compared in apparently damaged and healthy leaves. Only iodine concentration was markedly high in the damaged leaves.
4) A field survey for the leaf damages in eight plant species was conducted near a iodine refinery. Some leaves showed the symptoms of chlorosis or necrosis, and in those damaged leaves the iodine concentration was high.
From these results it was considered that the damages of pear leaves was caused by the excessive accumulation of iodine, which was probably emitted from a iodine refinery. The threshold of iodine concentration in pear leaves was 20-50ppm in sensitive cultivars Kosui and Hakko.
