Patterns of resistance to ALS-inhibitors in Cyperus difformis and Schoenoplectus mucronatus at whole plant level

Populations of Cyperus difformis L. (smallflower umbrella sedge) and Schoenoplectus mucronatus (L.) Palla (rice bulrush) resistant to ALS-inhibitor herbicides have been reported in several rice areas of the world. To investigate the common traits of C. difformis and S. mucronatus resistant to ALS-inhibitors in Italy, California and Spain, a joined research program has been developed. This contribution reports the preliminary results of a study carried out in the greenhouse at the whole-plant level on 7 populations of C. difformis and 4 of S. mucronatus collected in Italian, Spanish and California rice fields. The following ALS-inhibitors were tested: bensulfuron-methyl, halosulfuron, cinosulfuron, imazamox, and bispyribac-sodium. The study indicated the presence of both simple and cross resistance in the two species. On the basis of GR50, GR90 and Resistance Index (RI) values, complex resistance patterns among the tested populations were observed. Further laboratory studies on enzymatic activity and molecular traits of ALS of tested populations have to be completed to explain the observed resistance patterns.