Resistance Mechanism of Propanil-Resistant Barnyardgrass: II. In-vivo Metabolism of the Propanil Molecule

Abstract

Propanil-resistant barnyardgrass populations, previously veriÐed in Arkansas rice Ðelds and in greenhouse tests, were examined in the laboratory to ascertain if the resistance mechanism in this weed biotype was herbicide metabolism. Propanil-resistant barnyardgrass was controlled [95% in the greenhouse when carbaryl (an aryl acylamidase inhibitor) was applied two days prior to propanil. Laboratory studies with 14C-radiolabelled propanil indicated that the herbicide was hydrolysed in propanil-resistant barnyardgrass and rice to form 3,4-dichloroaniline, but no detectable hydrolysis occurred in susceptible barnyardgrass. Two additional polar metabolites were detected in propanil-resistant barnyardgrass and rice and tentatively identiÐed by thin layer chromatography. Overall, metabolites in the resistant barnyardgrass had values similar to those R f in rice, indicating similar metabolism for both species. These data, coupled with data from a previous report on the resistant biotype showing no di †erential absorption/translocation or molecular modiÐcation of the herbicide binding site in the resistant biotype, indicate that the resistance mechanism is metabolic degradation of propanil.

Metabolism-Based Herbicide Resistance and Cross-Resistance in Crop Weeds: A Threat to Herbicide Sustainability and Global Crop Production

“…However, it is more likely that the expression of several existing P450s (and other genes) contributing to the basal level of herbicide metabolism in a weedy plant could be simultaneously upregulated through a regulatory cascade, endowing resistance to a wider range of herbicides. In addition, it has long been known that metabolic resistance to the rice-selective herbicide propanil in Echinochloa crus-galli and Echinochloa colona is due to rapid propanil hydrolysis catalyzed by the enzyme aryl acylamidase (Leah et al, 1995;Carey et al, 1997), similar to that occurring in tolerant rice. Several organophosphate insecticides/herbicides can be used as synergists to combat the aryl acylamidase-endowed resistance (for review, see Hoagland et al, 2004).…”

“…Metabolic resistance can be endowed by increased activity of endogenous cytochrome P450 monooxygenases (P450s), glucosyl transferases (GTs), glutathione S-transferases (GSTs), and/or other enzyme systems such as aryl acylamidase (Carey et al, 1997) that can metabolize herbicides. P450s, GTs, and GSTs belong to major enzyme superfamilies with many roles in primary and secondary metabolism, and, by chance, some of them achieve herbicide detoxification (Kreuz et al, 1996;Cole and Edwards, 2000;Edwards and Dixon, 2000;Werck-Reichhart et al, 2000;Morant et al, 2003;Siminszky, 2006;Yuan et al, 2007).…”

Herbicide resistance in weeds endowed by enhanced detoxification: complications for management

“…Studies on the mechanism of resistance determined that resistance was the result of increased propanil detoxification, catalyzed by AAA in both species (Carey et al 1997;Leah et al 1994). The resistant plants degraded propanil more rapidly and more completely than did susceptible plants (Leah et al 1995; Figure 1).…”

Herbicide resistance work in the United States Department of Agriculture—Agricultural Research Service

“…Because of its effectiveness, propanil has been used at least once a year on 98% of the rice acreage in the USA, which creates a considerable selection pressure for resistance to appear 47. Propanil‐resistant barnyardgrass ( Echinochloa crus‐galli Beauv) was found in about half of the rice‐producing counties of Arkansas in the early 1990s and also in the neighboring areas of Mississippi, Louisiana and Texas 48, 49. ARS scientist Robert Hoagland, together with University of Arkansas scientists Jason Norsworthy, Frank Carey and Ronald Talbert, investigated these putative resistant biotypes.…”