Mechanism of isoproturon resistance: the metabolism of isoproturon in susceptible and resistant biotypes of Phalaris minor

Possible mechanisms of resistance to the photosynthetic inhibiting herbicid e isoproturon were examined in a resistant biotype of Phalaris minor from I ndia. Experiments were conducted under controlled and field conditions to e valuate metabolic fate of isoproturon. The resistant biotype tolerated a th ree times higher dose than the susceptible biotype. In a field experiment, isoproturon was completely degraded in 8 days in the resistant biotype and wheat, but persisted up to 18 days in the susceptible biotype. The toxic mo nodesmethyl and didesmethyl analogues were found in the susceptible biotype for up to 18 days. In the resistant biotype and wheat, two additional nont oxic metabolites, p-isopropyl aniline and a hydroxy derivative, were detect ed from 8 days onward confirming that metabolism of isoproturon in resistan t P. minor was similar to that in wheat.