METABOLISM OF DICLOFOP-METHYL IN SUSCEPTIBLE AND RESISTANT BIOTYPES OF LOLIUM-RIGIDUM

Differential metabolism and detoxication of the postemergence graminicide diclofop-methyl (DM) [methyl 2-(4-(2′,4′-dichlorophenoxy)phenoxy)propanoate] is not the basis for selectivity between the DM resistant (R) and susceptible (S) biotypes of Lolium rigidum. Metabolism of DM did not differ significantly between the two biotypes. DM metabolism in Lolium sp. resembled that of susceptible oat and wild oat (Avena sp.) and not resistant wheat (Triticum aestivum). Metabolism of DM was assayed in excised shoots, roots and leaves (leaf surface-applied DM) of R and S Lolium biotypes. Higher concentrations of phytotoxic diclofop (acid) remained in shoots and roots of R and S Lolium biotypes (42 to 47% of absorbed DM after 72 hr in roots), than was found in susceptible oat. Conjugates of both diclofop (ester conjugate) and aryl hydroxylated diclofop (phenolic conjugate) were formed in Lolium sp. Aryl hydroxylation may be slightly higher in roots than in shoots of both biotypes but hydroxylation was less than in resistan wheat. The mode of action of DM in the S biotype of Lolium is probably similar to that in susceptible Avena sp. since the phytotoxicity of DM in both species is reversed by 2,4-dichlorophenoxyacetic acid. © 1991.