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Physiology and Biochemistry

Effects of Organophosphorous Pesticides on Cutinase Activity and Infection of Papayas by Colletotrichum gloeosporioides. Martin B. Dickman, Graduate student, Department of Plant Pathology, University of Hawaii, Honolulu 96822; Suresh S. Patil(2), and P. E. Kolattukudy(3). (2)Professor, Department of Plant Pathology, University of Hawaii, Honolulu 96822; (3)Professor, Institute of Biological Chemistry, Washington State University, Pullman 99164. Phytopathology 73:1209-1214. Accepted for publication 15 February 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1209.

Thirteen pesticides, predominantly organophosphates, were shown to be potent inhibitors, in vitro, of purified cutinase of Colletotrichum gloeosporioides, the causal agent of papaya anthracnose. The I₅₀ values (concentration at which the enzyme activity is inhibited 50%) of these inhibitors ranged from 10^-3 to 10^-6 M. Four of these inhibitors were further studied to determine their K_i values for the cutinase. O, O-diethyl-O-(3,5,6-trichloro-2-pyridyl) phosphate. Hinosan, chlorpyrifos, and Inezin had K_i values of 10^-8 M, 2.3 x 10^-4 M, 2.6 x 10^-4 M, and 1.2 x 10^-4 M, respectively, which generally correlated with their I₅₀ values. The same four compounds and O,O-dimethyl-O-(2,4,5-trichlorophenyl)phosphate at micromolar or lower concentrations also effectively prevented infection of papaya in a laboratory fruit bioassay. None of the compounds was fungitoxic at these concentrations. An anionic detergent, sodium dodecyl sulfate (SDS), was shown to be a reversible inhibitor (K_i, 2.9 x 10^-4 M) of cutinase produced by C. gloeosporioides. SDS also prevented infection of papaya tissues; at 0.02, 0.2, and 2.0 mM SDS reduced infection by 53, 71, and 82%, respectively.