RESISTANCE MECHANISM OF PROPANIL-RESISTANT BARNYARDGRASS .1. ABSORPTION, TRANSLOCATION, AND SITE OF ACTION STUDIES

Resistance of barnyardgrass (Echinochloa crus-galli) to propanil, an important herbicide for controlling weeds in rice, has been discovered in Arkansas. Laboratory studies were conducted using resistant and susceptible barnyardgrass biotypes and C-14-radiolabeled propanil to determine if differential adsorption/translocation of propanil was responsible for resistance and to determine if an altered propanil binding site existed in the resistant biotype. Absorption and translocation of propanil were not significantly different in the resistant and susceptible barnyardgrass biotypes. Chlorophyll fluorescence data from leaf disks exposed to propanil showed that the herbicide binding site in the electron transport chain of PS II was also not altered in the resistant biotype. This biotype was not cross-resistant to other herbicides that inhibit PS II(atrazine, diuron, fluometuron, or linuron) because both biotypes had equal mortality rates when treated with recommended concentrations of these herbicides in the greenhouse, and low levels of atrazine (50 mu M) totally inhibited PS II in chlorophyll fluorescence tests of both biotypes. Thus, propanil resistance in this barnyardgrass biotype is not due to differential absorption, translocation, or modification of the herbicidal site of action. (C) 1995 Academic Press. Inc.