Oxalic acid and calcium oxalate produced by Leucostoma cincta and L. persoonii in culture and in peach bark tissues

Oxalic acid and crystals of calcium oxalate were produced during growth of Leucostoma cincta and L. persoonii on potato dextrose agar and in peach bark tissues. The identification of calcium oxalate was based on solubility characteristics, the results of KMnO4 titration, positive staining with silver nitrate – dithiooxamide, and crystal morphology as observed with light and scanning electron microscopes. Oxalic acid was detected by gas chromatography. This is the first report of oxalic acid production by both Leucostoma species causing peach canker. Calcium oxalate crystals observed on or near hyphae in culture were similar to crystals in artificially inoculated peach bark tissues. Addition of oxalic acid solutions alone to inner bark tissues caused maceration and necrosis. These results indicate a role for oxalic acid in the early stages of pathogenesis by Leucostoma spp. Tetragonal (bipyramidal) and prismatic calcium oxalate crystals formed on bark wounds treated with oxalic acid solutions were similar to those observed in infected tissues and in culture media amended with oxalic acid.