Rapid metabolic inactivation is the basis for cross-resistance to chlorsulfuron in diclofop-methyl-resistant rigid ryegrass (Lolium rigidum) biotype

Herbicide Metabolism in Weeds — Selectivity and Herbicide Resistance

“…Metabolism of chlorsulfuron in wheat took place at a higher rate than any ryegrass biotype having half-life of 2 h. Major metabolite of chlorsulfuron metabolism was identical in wheat and ryegrass biotypes, the glycosylated derivative of chlorsulfuron hydroxylated in the phenyl ring [51]. The metabolic detoxication of chlorsulfuron was faster in both roots and shoots of the resistant rigid rygrass biotype SR4/84 than in susceptible biotype SRS2, and the chlorsulfuron sensitivity between these biotypes could be explained by differential rate of metabolism [59]. Despite the correlation between enhanced metabolism and reduced plant sensitivity, no quantitative agreement can be described.…”

HRAC Classification of Herbicides and Resistance Development

“…ACCase resistance was subsequently also confirmed for L. multiflorum biotypes from other countries. In a resistant biotype selected by diclofop in Normandy, the resistance factor (ratio of the IC 50 for ACCase from the resistant to the IC 50 for ACCase from the susceptible biotype) was 19 for diclofop and 5 for haloxyfop, but only 2 for the CHDs clethodim and sethoxydim [33]. Interestingly, a different ACCase resistance pattern was found for the resistant L. multiflorum biotype Yorks A2, though field selection was apparently also mainly by diclofop.…”

“…The half-life of chlorsulfuron in susceptible plants was longer in the roots (13 h) than in the shoots (4 h) and was reduced in the resistant biotype to 3 and 1 h, respectively. Detoxification of the herbicide by ring hydroxylation, likely catalyzed by a cytochrome-P450 monooxygenase with subsequent glucose conjugation was enhanced in the resistant biotype [50].…”

“…While resistance of Lolium rigidum to ALS-inhibitors was attributed to enhanced herbicide metabolism [50] it was shown, for Lolium perenne and dicotyledonous species like Stellaria media, Kochia scoparia, Salsola iberica and Lactuca serriola, that resistant biotypes had a mutated ALS with reduced susceptibility to ALS-inhibiting herbicides [51][52][53]. The IC 50 s for sulfonylureas, which were determined in vitro with ALS isolated from Stellaria media, Salsola iberica and Lolium perenne, increased 4-to 50-fold in the resistant biotypes.…”

Differential Induction of Cytochrome P450-Mediated Triasulfuron Metabolism by Naphthalic Anhydride and Triasulfuron

“…For a number of herbicides, resistance in tolerant plants is known to be mediated by the rapid conversion of the herbicide into hydroxylated, inactive products (Frear et al, 1991) * Corresponding author; e-mail maryschu8uiuc.edu; fax 1-21 7-244-1336, subsequently conjugated to carbohydrate moieties in the plant cell wall (Lamoureux and Rusness, 1986). In many of these cases, the involvement of P450s in the initial steps of herbicide detoxification was originally inferred from in vivo analysis of tolerant versus susceptible biotype plants (Christopher et al, 1991;Cotterman and Saari, 1992). More recently, definitive in vitro P450-mediated metabolism of herbicides has been demonstrated for the N-demethylation and ring methyl hydroxylations of chlortoluron (a phenylurea herbicide) in wheat (Mougin et al, 1990) and maize , the aryl hydroxylations of diclofop in wheat (McFadden et al, 1989;Zimmerlin and Durst, 1990, 19921, the aryl hydroxylation of triasulfuron and chlorsulfuron (sulfonylurea herbicides) in wheat (Frear et al, 1991;Thalacker et al, 1994) and maize (Moreland et al, 1993a), and the aryl-and pyrimidine-ring hydroxylations of primisulfuron (a sulfonylurea herbicide) in maize .…”