Corn poppy (Papaver rhoeas) cross‐resistance to ALS‐inhibiting herbicides

BACKGROUND: Papaver rhoeas (L.) has evolved resistance to tribenuron in winter wheat fields in northern Greece owing to multiple Pro(197) substitutions. Therefore, the cross-resistance pattern to other sulfonylurea and non-sulfonylurea ALS-inhibiting herbicides of the tribenuron resistant (R) and susceptible (S) corn poppy populations was studied by using whole-plant trials and in vitro ALS catalytic activity assays. RESULTS: The whole-plant trials revealed that tribenuron R populations were also cross-resistant to sulfonylureas mesosulfuron + iodosulfuron, chlorsulfuron and triasulfuron. The whole-plant resistance factors (RFs) calculated for pyrithiobac, imazamox and florasulam ranged from 12.4 to > 88, from 1.5 to 28.3 and from 5.6 to 25.4, respectively, and were lower than the respective tribenuron RF values (137 to > 2400). The ALS activity assay showed higher resistance of the ALS enzyme to sulfonylurea herbicides (tribenuron > chlorsulfuron) and lower resistance to non-sulfonylurea ALS-inhibiting herbicides (pyrithiobac > florasulam ≈ imazamox). CONCLUSION: These findings indicate that Pro(197) substitution by Ala, Ser, Arg or Thr in corn poppy results in a less sensitive ALS enzyme to sulfonylurea herbicides than to other ALS-inhibiting herbicides. The continued use of sulfonylurea herbicides led to cross-resistance to all ALS-inhibiting herbicides, making their use impossible in corn poppy resistance management programmes.