EFFECT OF MONOOXYGENASE INHIBITORS ON UPTAKE, METABOLISM AND PHYTOTOXICITY OF PROPANIL IN RESISTANT BIOTYPES OF JUNGLE-RICE, ECHINOCHLOA-COLONA

The effect of the mono-oxygenase inhibitors tridiphane, piperonyl buto xide and prochloraz on propanil uptake, metabolism and phytotoxicity w as measured in a resistant (R) biotype of Echinochloa colona. The upta ke of propanil was not significantly affected by any of the three mono -oxygenase inhibitors. The first metabolite of propanil metabolism, 3, 4-dichloroaniline, was found to accumulate to higher levels in E. colo na treated with each of the mono-oxygenase inhibitors mixed with formu lated propanil, compared to propanil applied alone. Accumulation of fu rther metabolites of propanil (glucosyl-3,4-dichloroaniline and bound products) was reduced in the presence of mono-oxygenase inhibitors, co mpared with propanil application alone. Leaf damage caused by a single drop of propanil compared to propanil + mono-oxygenase inhibitor was used to assess the degree of propanil tolerance in E. colona biotypes. Leaf damage was significantly greater in propanil + mono-oxygenase in hibitor treatments. No leaf damage was observed in mono-oxygenase inhi bitor treatments alone at the concentrations used. Peroxidase activity was measured in crude extracts of the R-biotype of E. colona using 3, 4-dichloroaniline as substrate, in the presence and absence of mono-ox ygenase inhibitors and the specific peroxidase inhibitor salicylhydrox amic acid. Peroxidase activity was inhibited by all three monooxygenas e inhibitors at 10 mu M and by salicylhydroxamic acid at 1 mu M. Gluco syl-3,4-dichloroaniline was found not to be a substrate for peroxidase activity. These results suggest that the incorporation of 3,4-dichlor oaniline into bound residues involves peroxidase activity which can be inhibited by mono-oxygenase inhibitors. When peroxidase activity is i nhibited, the precursor metabolite 3,4-dichloroaniline accumulates, an d propanil resistance in E. colona is reduced, possibly as a consequen ce of phytotoxicity of this metabolite and/or product inhibition of th e first step in propanil metabolism, responsible for the formation of 3,4-dichloroaniline. Glasshouse trials have demonstrated that the appl ication of mono-oxygenase inhibitors, (particularly tridiphane which i s also known to inhibit glutathione transferase activity) with propani l offers a promising approach to the control of propanil resistant bio types of Jungle-Rice.