psbA mutation (valine(219) to isoleucine) in Poa annua resistant to metribuzin and diuron

The herbicide-binding region of the chloroplast psbA gene from a total of 2 0 biotypes of Poa annua L resistant and susceptible to metribuzin and diuro n was selectively amplified using PCR. Sequence analysis of the fragment fr om six herbicide-resistant biotypes of P annua exhibited a substitution fro m valine to isoleucine at position 219 of the D1 protein encoded by the psb A gene. This is the same mutation as reported for Chlamydomonas and Synecho coccus through site-directed mutagenesis and in cell cultures of Chenopodiu m rubrum L. To our knowledge this is the first report of a higher plant exh ibiting resistance in the field to photosystem II inhibitors due to a psbA mutation other than at position 264. The existence of additional biotypes o f P annua resistant to diuron or metribuzin but lacking mutation in the her bicide-binding region indicates that resistance to these herbicides can als o be attained by other mechanisms. (C) 2000 Society of Chemical Industry.