|Park, Kee Wong - OREGON STATE UNIVERSITY|
|Mallory-Smith, Carol - OREGON STATE UNIVERSITY|
|Ball, Daniel - OREGON STATE UNIVERSITY|
|Mueller Warrant, George|
Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 15, 2004
Publication Date: October 31, 2004
Citation: Park, K., Mallory-Smith, C.A., Ball, D.A., Mueller Warrant, G.W. 2004. Ecological fitness of acetolactate synthase inhibitor–resistant and –susceptible downy brome (bromus tectorum) biotypes. Weed Science.52(5):768-773. Interpretive Summary: When herbicide-resistant and –susceptible biotypes differ in their ecological fitness it is possible to develop herbicide resistance management strategies to either decrease the prevalence of the resistant biotype in the environment or slow its spread into new areas. In the case of an ALS-resistant biotype of downy brome found in eastern Oregon, differences in ecological fitness between it and a susceptible biotype were minimal, suggesting that slowing the spread of this resistant biotype will be difficult to achieve.
Technical Abstract: Studies were conducted to determine the relative fitness and competitive ability of an acetolactate synthase (ALS) inhibitor–resistant (R) downy brome biotype compared with a susceptible (S) biotype. In previous research, the mechanism of resistance was determined to be an altered ALS enzyme. Seed germination of the R biotype was compared with that of the S biotype at 5, 15, and 25 C. There were no different germination characteristics between R and S biotypes at 15 and 25 C. However, the R biotype germinated 27 h earlier than the S biotype and had reached over 60% germination when the S biotype initially germinated at 5 C. Under noncompetitive greenhouse conditions, growth of the R biotype was similar to that of the S biotype on the basis of shoot dry weight, leaf area, and plant height. Seed production of the R biotype was 83%, when compared with the S biotype, but seeds of the R biotype were larger than those of the S biotype. Replacement series experiments were conducted in the greenhouse to determine the relative competitive ability of R and S biotypes. No difference in competitive ability was observed between R and S biotypes on the basis of shoot dry weight, leaf area, or plant height. Thus, it appears that ALS-resistance trait is not associated with growth penalty in either noncompetitive or competitive conditions. In the absence of ALS inhibitors, these results suggest that the R biotype would remain at a similar frequency in a population of R and S biotypes.