Title: Cross-resistance to three frequently used sulfonylurea herbicides in populations of Apera spica-venti from the Czech Republic
Abstract: Whole-plant glasshouse bioassays, enzyme assays and field experiments were conducted to examine the sulfonylurea herbicide resistance pattern in Apera spica-venti populations from the Czech Republic. Varying, but very high levels of resistance to chlorsulfuron, sulfosulfuron and iodosulfuron were found, and cross-resistance to all three herbicides was confirmed. In dose–response glasshouse studies, resistance factors (GR50 ratios relative to a susceptible standard) were above 230 for chlorsulfuron, 115–270 for sulfosulfuron and 27–148 for iodosulfuron. A biotype originating from Lomnice that was cross resistant to the three herbicides was also highly resistant to sulfometuron-methyl. Concentrations of herbicides required to inhibit acetolactate synthase (ALS) enzyme activity by 50% were substantially higher (up to 4000 times) for all three resistant populations, compared with the reference susceptible population, indicating that the A. spica-venti populations have ALS enzymes that are highly insensitive to the tested sulfonylureas. The differences in the spectra of resistance suggest that the sulfonylurea resistance mechanisms may differ among biotypes. The field experiment was designed to compare the control effect of selected sulfonylureas (chlorsulfuron and iodosulfuron), isoproturon and fenoxaprop-P-ethyl on ALS-resistant populations. Sulfonylurea herbicides failed to control resistant populations, but these were well controlled with alternative mode of action herbicides, thus demonstrating practical options for weed management. [Hamouzová K, Soukup J, Jursík M, Hamouz P, Venclová V & Tůmová P (2010). Cross-resistance to three frequently used sulfonylurea herbicides in populations of Apera spica-venti from the Czech Republic. Weed Research. on-line 11 Oct., DOI: 10.1111/j.1365-3180.2010.00828.x]