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

Resistance of barnyardgrass (Echinochloa crus-galli) to propanil, an i mportant herbicide for controlling weeds in rice, has been discovered in Arkansas. Laboratory studies were conducted using resistant and sus ceptible barnyardgrass biotypes and C-14-radiolabeled propanil to dete rmine if differential adsorption/translocation of propanil was respons ible for resistance and to determine if an altered propanil binding si te existed in the resistant biotype. Absorption and translocation of p ropanil were not significantly different in the resistant and suscepti ble barnyardgrass biotypes. Chlorophyll fluorescence data from leaf di sks exposed to propanil showed that the herbicide binding site in the electron transport chain of PS II was also not altered in the resistan t biotype. This biotype was not cross-resistant to other herbicides th at inhibit PS II(atrazine, diuron, fluometuron, or linuron) because bo th biotypes had equal mortality rates when treated with recommended co ncentrations 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 barnyardgra ss biotype is not due to differential absorption, translocation, or mo dification of the herbicidal site of action. (C) 1995 Academic Press. Inc.