|Mueller Warrant, George|
Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/1999
Publication Date: 1/31/2000
Interpretive Summary: Herbicide resistant mutants of the weed annual bluegrass were found in grass seed fields in western Oregon. We used polymerase chain reaction (PCR) techniques (DNA fingerprinting) to study genetic diversity of this weed. We also examined the DNA sequence of an important chloroplast gene, psbA. The protein made from psbA is involved in the flow of energy from sunlight to chemical energy. Plants from several different fields we found to have a specific mutation in this gene that would interfere with th binding of several commonly used herbicides, diuron and metribuzin. This mutation has never before been found out in the wild. Plants with this mutation were able to survive higher rates of these herbicides, and have proliferated in the field, causing problems for grass seed growers. Other plants were found that resisted these herbicides without having this psbA mutation, suggesting that they possess other mechanisms of resistance.
Technical Abstract: The herbicide-binding region of the chloroplast psbA gene from biotypes of Poa annua L. resistant and susceptible to metribuzin and diuron was selectively amplified using PCR. Sequence analysis of the fragment from six herbicide-resistant biotypes of P. annua exhibited a substitution from valine to isoleucine at position 219 of the D1 protein encoded by the psbA gene. This is the same mutation as reported for Chlamydomonas and Synechococcus through site-directed mutagenesis and in cell cultures of Chenopodium rubrum L. To our knowledge this is the first report of a higher plant exhibiting resistance in the field of photosystem II inhibitors due to psbA mutation other than position 264. The existence of additional bio- types of P. annua resistant to diuron or metribuzin but lacking mutation in the herbicide-binding region indicates that resistance to these herbicides can also be attained by other mechanisms.