VIEW ARTICLE

Physiology and Biochemistry

Induction of Polygalacturonase from Rhizoctonia solani by Cotton Seed and Hypocotyl Exudates. L. W. Brookhouser, Former graduate assistant, Department of Plant Pathology, University of California, Berkeley, CA 94720, Present address of senior author: Diamond Shamrock Corporation, Cleveland, OH; A. R. Weinhold, professor, Department of Plant Pathology, University of California, Berkeley, CA 94720. Phytopathology 69:599-602. Accepted for publication 18 December 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-599.

Endopolygalacturonase (EPG) first was detected in 0.5 M NaCl extracts collected from cotton seedling hypocotyls 18 hr after inoculation with Rhizoctonia solani. The units of EPG activity in extracts collected 12, 18, 24, 48, and 72 hr after inoculation were 0, 17.5, 36.0, 39.6, and 28.8, respectively. By 18 hr after inoculation, infection cushions had formed, and by 22–24 hr the hypocotyl tissue beneath the cushions was slightly discolored. Neither pectin lyase nor pectate lyase was detected in any of the extracts. The fungus produced extracellular EPG in 0.1% sodium polypectate, in nondialyzed seed exudates, and in dialyzed seed exudates. At 24 hr after seeding with R. solani, the units of EPG activity in the above preparations were 28, 4, and 256, respectively. The seed exudates (1 ml/four seeds) were obtained by incubating cotton seeds in water at 22 C for 3 hr. The dialyzed and nondialyzed cotton seed exudates contained about 20 μg of galacturonic acid polymers per milliliter. Solutions obtained by exposing cotton hypocotyls to a commercial pectinase solution for 4 hr or to 0.05 M HCl for 1 hr, induced the fungus to produce 5.6 and 0.4 units, respectively, of EPG activity 24 hr after seeding. This study provides evidence that R. solani produces EPG in response to host exudates.