ABSENCE OF DIFFERENTIAL FITNESS BETWEEN GIANT FOXTAIL (SETARIA-FABERI) ACCESSIONS RESISTANT AND SUSCEPTIBLE TO ACETYL-COENZYME A CARBOXYLASE INHIBITORS

Experiments were conducted to determine the productivity, inter-, and intraspecific competitive ability of giant foxtail accessions resistan t (PCW1) and susceptible (AC1) to acetyl-coenzyme A carboxylase (ACCas e) inhibitors. Under noncompetitive conditions in the field, shoot dry biomass, plant height, and leaf area over time were similar between t he PCW1 and AC1 accessions. The instantaneous relative growth rate and instantaneous net assimilation rate did not differ between the access ions; however, the instantaneous leaf area ratio was slightly greater for the AC1 accession than the PCW1 accession. The seed yield was simi lar between the PCW1 and AC1 accessions. Addition series experiments w ere conducted in the field to determine the intraspecific competitive ability of the PCW1 and AC1 accessions. Regression surface analysis of reciprocal mean shoot dry biomass and seed yield indicated that the r elative competitive ability of the PCW1 and AC1 accessions was similar . Replacement series experiments were conducted in the greenhouse with or without corn to determine the interspecific competitive ability of the accessions. The relative growth rate, shoot dry biomass, and seed yield of the PCW1 and AC1 accessions were greater without than with c orn competition. The relative competitive ability of the PCW1 and AC1 accessions was similar with or without corn competition based on shoot dry biomass or seed yield. These results indicated that the intra- an d interspecific competitive ability of the PCW1 and AC1 giant foxtail accessions are similar and suggest that resistance to ACCase inhibitor s has not reduced the relative fitness of the PCW1 accession.