Jm. Leah et al., EFFECT OF MONOOXYGENASE INHIBITORS ON UPTAKE, METABOLISM AND PHYTOTOXICITY OF PROPANIL IN RESISTANT BIOTYPES OF JUNGLE-RICE, ECHINOCHLOA-COLONA, Pesticide science, 49(2), 1997, pp. 141-147
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.