Possible involvement of herbicide sequestration in the resistance to diclofop-methyl in Italian biotypes of Lolium spp.

susceptible) was investigated. The major proportion of R-1 (Tuscania 1997) and R-2 (Roma 1994) plants (approximately 80%) survived after herbicide treatment by emitting new tillers from the crown. Both resistant (R-I and R-2) and susceptible (Vetralla 1994) Lolium spp. populations were target-site sensitive. No difference in diclofop-methyl absorption by shoots of resistant and susceptible biotypes was observed. At the dose corresponding to 1x the recommended field rate, a relatively higher metabolism was found in R-2 biotype. In contrast. at the doses 2x and 10x the field rate no difference in herbicide metabolism between susceptible and resistant biotypes was observed. At all the three herbicide doses (1x, 2x, and 10x the field rate) 48 It after the treatment (HAT). the total amount of metabolites produced by wheat was more than three times higher than that produced by resistant and susceptible ryegrass biotypes. At the doses 1x and 2x the field rate, the herbicide translocation was different in the susceptible biotypes compared to resistant biotypes. The total amount of the radiolabel found 48 HAT in culm and root was approximately twice in susceptible biotype than in resistant biotypes. Susceptible and resistant ryegrass biotypes differed in the capability of their roots to acidify the external medium. Susceptible biotype acidified the external solution at approximately 6 times the rates of the resistant biotypes. In the present study, the mechanism responsible for resistance in the investigated resistant biot,pes was not univocally identified, Indirect evidence support, he possible involvement of herbicide sequestration or immobilization. (C) 2004 Elsevier Inc. All rights reserved.