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Oxalic Acid Production by Sclerotinia sclerotiorum in Infected Bean and in Culture. Douglas P. Maxwell, Assistant Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706; R. D. Lumsden, Research Plant Pathologist, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 60:1395-1398. Accepted for publication 14 April 1970. DOI: 10.1094/Phyto-60-1395.

Sclerotinia sclerotiorum produced oxalic acid in a liquid-salts-yeast extract medium (initial pH 5.8) supplemented with either 110 mm d-glucose, 110 mm d-glucose, and 0.2 m potassium phosphate, or 73.7 mm d-glucose, and 56.0 mm sodium succinate. Oxalic acid concn in these media were 0, 17.8, and 70.8 mm, respectively, after 7 days' growth at 26 C. Growth was equivalent on these media. On the glucose-succinate medium, fungal growth rate was correlated positively with rate of oxalate accumulation. Oxalic acid accumulation by 17 isolates varied from 1.4 to 78.3 mm in the glucosesuccinate medium. In bean hypocotyls infected by S. sclerotiorum (isolate Ss-3), oxalate was detected at 1.1, 31.4, and 48.3 mg/g dry wt of tissue 0, 2, and 4 days after inoculation, respectively. The pH value of tissue extracts was 6.1 on day 0, decreased to 4.1 on day 2, and increased to 5.8 on day 6. During the first 2 days after inoculation, 2-4 cm of the bean hypocotyl were colonized, and polygalacturonase activity of tissue extracts increased significantly. This study suggests the possibility that oxalic acid plays an important role in pathogenesis of S. sclerotiorum infections.