Evidence for co-occurrence of resistance to ALS inhibitors and 2,4-D in corn poppy (Papaver rhoeas).

Corn poppy (Papaver rhoeas) has long been associated with target-site and more recently non-target site resistance to ALS inhibitors (HRAC group B). Amounting evidence suggests that this species may also develop resistance to synthetic auxins (HRAC group O). The present study aimed at screening three P. rhoeas populations (F3B, F1D and F4C) from central Greece fields with a known history of group B and O herbicides, to identify populations where resistance to both herbicide groups may be present. Plants of these populations and of a reference population (S, 100% sensitive plants) were sprayed with an ALS inhibitor (iodosulfuron+mesosulfuron) or a synthetic auxin (2,4-D ester). Iodosulfuron+mesosulfuron was applied at 0, N and 4N, where N=250g ha-1 (recommended field rate) with 0.2% surfactant (sodium alkyl ether sulphate). S population was treated with iodosulfuron+mesulfuron at 0 and N. 2,4-D was applied at 0, 0.5N, N, 2N and 4N where N=345g ha-1 (recommended field rate). S population was treated with 2,4-D at 0.25N, 0.5N, N, and 2N. The experiment was performed in a glasshouse during April-May 2015 (15-25°C, natural photoperiod). The herbicides were applied with a bench sprayer fitted with one even-distribution flat-spray nozzle delivering 350L ha-1. Visual phenotype rating (dead or alive) was performed four weeks after treatment. At 4N iodosulfuron+mesosulfuron no plant survived in any population, whereas at N all S plants died but 44% F3B, 4% F1D and 13% F4C plants survived. At N 2,4-D all S plants died, whereas 54% F3B, 51% F1D and 48% F4C plants survived. At 2N 2,4-D all S plants died, whereas 32% F3B, 17% F4C and 30% F1D plants survived. The results show that one P. rhoeas population (F3B) contains plants with resistance to both ALS inhibitors and synthetic auxins, which has implications for future management of this species.