Effects of Organophosphorous Pesticides on Cutinase Activity and Infection of Papayas byColletotrichum gloeosporioides

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Abstract
Thirteen pesticides, predominantly organophosphates, are potent inhibitors in vitro of purified cutinase of C. gloeosporioides, the causal agent of papaya anthracnose. The I50 values (concentration at which the enzyme activity is inhibited 50%) of these inhibitors ranged from 10-3-10-9 M. Four of these inhibitors were further studied to determine their Ki values for the cutinase. O,O-Diethyl-O-(3,5,6-trichloro-2-pyridyl)phosphate, Hinosan, chlorpyrifos and Inezin had Ki values of 10-8 2.3 .times. 10-4 2.6 .times. 10-4 and 1.2 .times. 10-4 M, respectively, which generally correlated with their I50 values. The same 4 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), is a reversible inhibitor (Ki 2.9 .times. 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.