Solanum ptycanthum resistance to acetolactate synthase inhibitors

Solanum ptycanthum plants putatively resistant to acetolactate synthase (AL S) inhibitors were identified in a Wisconsin Glycine max field in 1999. Thr ee- to four-leaf-stage S. ptycanthum plants in the greenhouse were 150, 120 , and 5.9-fold resistant to imazethapyr, imazamox, and primisulfuron, respe ctively, compared with susceptible plants. In vivo ALS was 170- and less th an 20-fold more resistant to imazethapyr and primisulfuron, respectively. T hese results suggested that the S. ptycanthum accession was highly resistan t to imazethapyr and imazamox, and that resistance was associated with inse nsitive ALS. This is the first confirmed occurrence worldwide of S. ptycant hum resistance to ALS inhibitors.