Group 15 Pre-emergent Herbicides Differentially Effect Plant Growth, Cuticular Wax Composition, and Fatty Acid Metabolism in Herbicide-Resistant and Herbicide-naïve Blackgrass

Despite their long history of effective use in agroecosystems, the precise molecular mechanisms of many pre-emergent herbicides are not fully understood. This study investigates the effects of three Group 15 pre-emergent herbicides (Flufenacet, S-ethyl dipropylthiocarbamate (EPTC), and tri-allate) on two well-characterized blackgrass ( Alopecurus myosuroides ) biotypes. Blackgrass is the predominant weed threatening winter wheat production in North-West Europe and the effective use of pre-emergent herbicides is important for preventing otherwise difficult-to-control blackgrass from establishing in agricultural fields. Using a sterile, agar-based system, we quantified the effects of multiple doses of flufenacet, EPTC, or tri-allate on plant physiology, including germination and early seedling growth, as well as the effects of a single dose on key biochemical pathways, specifically cuticular wax composition and fatty acid metabolism in biotypes exhibiting either non-target site herbicide resistance or complete sensitivity to all tested herbicides. Our data demonstrate that the three Group 15 pre-emergent herbicides alter cuticular wax composition and fatty acid profiles differently and that the resistant and herbicide-naïve biotypes show distinct responses to each herbicide. The GC-FID and GC-MS data from the different Group 15 pre-emergent herbicides are consistent with the observed differences in physiology and identify potential differences in how and where these herbicides act in these biotypes. Our findings provide novel molecular insights into the mechanisms of action of and tolerance to flufenacet, EPTC, or tri-allate in blackgrass.