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Postharvest Pathology and Mycotoxins

Identification of Pectinases Produced in Cotton Bolls Infected with Aspergillus flavus. Thomas E. Cleveland, USDA/ARS, Southern Regional Research Center, New Orleans, LA 70179; Susan P. McCormick, USDA/ARS, Southern Regional Research Center, New Orleans, LA 70179. Phytopathology 77:1498-1503. Accepted for publication 20 May 1987. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1987. DOI: 10.1094/Phyto-77-1498.

Pectinases from Aspergillus flavus liquid cultures or cotton bolls wound-inoculated at 30 days postanthesis (DPA) with the same fungus were analyzed by isoelectric focusing. The same three A. flavus pectinases (P1, P2c, and P3) were detected in both liquid cultures containing pectin and the immature lint of inoculated 30 DPA bolls. Pectinase activity was first detected in lint and seed extracts 2 days after inoculation and increased to maximum level in 3–5 days. The major pectinase (P2c) of the three activities examined in both liquid media and infected bolls was identified and partially characterized. Rates of pectolytic-induced viscosity loss and production of reducing sugars, the pattern of release of oligogalacturonide fragments, and the absence of transeliminative products in reactions indicated that P2c was an endopolygalacturonate hydrolase. Activities of P1 and P3 but not P2c were subject to catabolite repression in fungal cultures containing glucose. The early accumulation and continued presence of pectinases within infected tissues suggested that they were involved in establishment of this fungus in locular tissues.