The fact that the in vitro AHAS activity
(from R biotypes) to various AHAS herbicides is highly correlated
with the whole-plant response to these herbicides and the estimated Pearson’srvalues for HB08 and HB16 are 0.996 and 0.912
respectively. These strongly suggest that the altered sensitivity of
the target enzyme is mainly responsible for the cross resistance
and hypersensitivity observed for some of the AHAS herbicides.
Whereas, the non-target site based resistance mechanisms have
involved in the resistance and cross resistance of various weed species including rigid ryegrass, rigid brome (Bromus rigidus), large
crabgrass (Digitaria sanguinalis), and late watergrass (Echinochloa
phyllopogon)[27–29]. Progresses on the non-target site based herbicide resistance were reviewed by Yun (2007) and Powles (2012)
[8,30]. Therefore, the non-target based resistance mechanisms in
two R biotypes of flixweed also could not be ruled out