VIEW ARTICLE

Physiology and Biochemistry

Role of Pectolytic Enzymes and Galacturonic Acid in Citrus Fruit Decay Caused by Penicillium digitatum. Charles R. Barmore, Associate professor, University of Florida, Institute of Food and Agricultural Sciences, Agricultural Research and Education Center, P.O. Box 1088, Lake Alfred, 33850; G. Eldon Brown, research scientist III, Florida Department of Citrus, Agricultural Research and Education Center, P.O. Box 1088, Lake Alfred, 33850. Phytopathology 69:675-678. Accepted for publication 18 January 1979 . Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-675.

Decay of citrus fruit by Penicillium digitatum was associated with content or activity of galacturonic acid, pectinmethylesterase (PME), and exopolygalacturonase (exo-PG). The pectolytic enzymes endopolygalacturonase or pectin transeliminase were not associated with the disease. The hydrolysis of pectic acid by exo-PG resulted in an accumulation of galacturonic acid up to 12 mg/g fr wt within the lesion. Treatment of thin citrus peel sections with galacturonic acid, PME, or exo-PG did not induce cell separation. However, reduction in tissue strength was apparent with serial treatments of galacturonic acid, PME, and exo-PG. Each of these three constituents caused specific cellular changes which collectively resulted in a weakening of the cell wall. A possible role for each of these constituents in decay of citrus fruit by P. digitatum is discussed.