Cytochrome P450 metabolism-based herbicide resistance to imazamox and 2,4-D in Papaver rhoeas

Papaver rhoeas biotypes displaying multiple herbicide resistance to ALS inhibitors and synthetic auxin herbicides (SAH) are spreading across Europe. In Spain, enhanced metabolism to imazamox was confirmed in one population, while cytochrome-P450 (P450) based metabolism to 2,4-D in another two. The objectives of this research were to further confirm the presence of P450 mediated enhanced metabolism and, if so, to confirm whether a putative common P450 is responsible of metabolizing both 2,4-D and imazamox. Metabolism studies were undertaken in five P. rhoeas populations with contrasted HR profiles (herbicide susceptible, only HR to ALS inhibitors, only HR to SAH, or multiple HR to both), and moreover, three different P450 inhibitors were used. The presence of enhanced metabolism to these SoA was confirmed in three more HR P. rhoeas populations. This study provides the first direct evidence that imazamox metabolism in these biotypes is P450-mediated, also in one population without an altered target site. Additionally, it was further confirmed that enhanced metabolism of 2,4-D in biotypes only HR to SAH or multiple HR to ALS inhibitors and SAH involves P450 as well. No metabolism was detected using the three inhibitors in all the herbicide-metabolizing P. rhoeas biotypes, suggesting that a common metabolic system involving P450s is responsible of degrading herbicides affecting both SoAs. Thus, selection pressure with either SAH or imidazolinone ALS inhibitors can select not only for resistance to each of them, but it can also confer cross-resistance between them in P. rhoeas.