Characterization of wild oat (Avena fatua L.) populations and an inbred line with multiple herbicide resistance

Repeated use of the pre-emergence herbicide triallate has selected for wild oat populations that are resistant (R)³ to field use rates. Field collections and an inbred R line were shown in greenhouse and petri dish dose response experiments to be 6- to 20-fold more tolerant to triallate than susceptible (S)³ lines. R populations and the inbred line were also resistant (8-fold) to the related thiocarbamate herbicide diallate, as well as to the chemically unrelated postemergence herbicide difenzoquat (60- fold). ¹⁴C-triallate uptake and translocation patterns were similar between R and S lines for the first 24 h after application. However, translocation of radioactivity was more rapid in S lines than R lines from 24 through 60 h after application. ¹⁴C-difenzoquat uptake was the same in R and S lines 12 h after application, but was 10 to 20% higher in R lines than S lines by 24 through 96 h after application. Similarly, translocation of radioactivity after ¹⁴C-difenzoquat application was 7 to 14% greater in R than S lines after 12 h, although translocated radioactivity amounts were not significantly different between R and S lines. The relatively minor differences in triallate and difenzoquat uptake and translocation patterns between R and S lines are most likely not of sufficient magnitude to explain the observed resistance levels.