6533b7d0fe1ef96bd125a129

RESEARCH PRODUCT

False cleavers (Galium spurium L.) with target-site resistance to ALS inhibiting herbicides in Greece

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Galium spurium(Rubiaceae) is a frequent troublesome dicotyledonous weed species, usually controlled with ALS inhibitors, synthetic auxins and their mixtures. In 2016, florasulam+2,4-D failed to adequately control this species in cereal fields (Phthiotida, central Greece) prompting the current study. Seeds from three G. spurium populations (G2, G3, G4) with possible resistance and one from herbicide-free field borders (G1, reference) were collected. These were evaluated in a pot experiment for possible resistance to ALS inhibitors at 0, N and 4N (N= recommended field dose: florasulam+2,4-D 4.375+210 g/ha, florasulam 6.25 g/ha, mesosulfuron+iodosulfuron 7.5+7.5 g/ha) with four replicates (five plants/replicate). Mecoprop-p (N= 1050 g/ha) was included as a non-ALS chemical control. Herbicides were applied at the four-six whorl stage of foliar development. Six weeks after treatment, plants were visually scored (VS) on a ten-level scale (0=dead, 10=as unsprayed control) and cut at soil level for fresh weight (FW) measurement. Leaf samples from surviving plants with the highest VS at 4N were collected for ALS sequencing. Mecoprop-p provided 100% control of all populations. Mesosulfuron+iodosulfuron at N fully controlled population G1 (100% plants with VS=0-3) but failed even at 4N to control populations G2, G3 (0% dead plants, 15-16% FW reduction) and G4 (15% dead plants, 47% FW reduction). Florasulam+2,4-D at N moderately controlled population G1 (80% plants with VS=0-3, 69% FW reduction) but failed to control populations G2, G3 and G4, even at 4N (0% dead plants, 4-19% FW reduction). Control with florasulam was complete for G1 only at 4N (100% plants with VS=0-3) but failed for all other populations (0% dead plants at 4N). ALS sequencing revealed a Trp574Leu mutation in populations G2, G3 and G4, confirming target-site resistance to ALS inhibitors in G. spurium, for the first time in Europe. Further work is underway, with dose-response experiments and ALS enzyme activity assays.