Selectivity of Clomazone for rice plants increases when seeds are treated with the safener dietholate. Considering that dietholate acts on the activity of the cytochrome P450 monooxigenase, and that this enzyme also activates the herbicide clomazone, other chemicals capable of acting as safeners should also be sought. Thus, a trial was conducted aiming to evaluate the protective effect of dietholate and phorate against increasing clomazone rates. The trial was carried out in a completely randomized block design, with four replicates in a factorial scheme. Factor A included seeds untreated and treated with dietholate or with phorate. Factor B included eight clomazone rates (0, 156, 312, 625, 1,250, 2,500, 5,000 and 10,000 g a.i. ha-1). Plant injury, plant height reduction percentage, fresh mass and dry mass weight were evaluated 18 days after sowing. Data were submitted to analysis of variance by non-linear regression of the logistic type. Significant differences were observed between the control without safener and the treatments with dietholate or phorate. The dose-response curves showed that when rice seeds were treated with either dietholate or phorate, the rice plants were able to tolerate higher rates of clomazone, compared to the untreated control. Thus, this study shows that dietholate and phorate inhibit the enzyme cytochrome P-450, blocking the activation of clomazone in the rice plants.
cytochrome P-450; phytotoxicity; safener
