Response of Herbicide-Resistant Palmer Amaranth (Amaranthus palmeri) Accessions to Drought Stress

Palmer amaranth is a very problematic weed in several crops in the southern USA due to its competitive ability and resistance to herbicides representing different mechanisms of action. Variation in growth and subsequent interference of North Carolina Palmer amaranth accessions has not been examined. A greenhouse experiment determined response of 15 North Carolina Palmer amaranth accessions to drought stress beginning 15 days after seedling emergence (DAE) for a duration of 3, 5, 7, and 9 days. Following exposure to drought, plants were grown under optimal moisture conditions until harvest at 30 DAE. Five accessions each of glyphosate-resistant (GR), acetolactate synthase inhibitor-resistant (ALSR), and acetolactate synthase inhibitor-susceptible and glyphosate-susceptible (ALSS/GS) were compared. Variation in response to drought stress, based on height and dry weight reduction relative to nonstressed controls, was noted among accessions. Stress for 3 or more days affected height and dry weight. Height and dry weight of GR and ALSR accession groups were reduced less by drought than the ALSS/GS accession group. Results suggest a possible relationship between herbicide resistance and ability of Palmer amaranth to withstand drought stress and thus a possible competitive advantage for resistant accessions under limited moisture availability.