ALS Gene Mutations in Apera Spica-Venti Confer Broad-Range Resistance to Herbicides Several biotypes of wind bentgrass in Poland have been identified as being resistant to acetolactate synthase (ALS) inhibitors. We screened these weeds with chlorsulfuron and performed a whole-plant bioassay with a range of doses based on these four herbicides: chlorsulfuron, sulfosulfuron, propoxycarbazone-sodium and mesosulfuron-methyl + iodosulfuron-methyl-sodium mixture. Ten biotypes, diverse in their levels of resistance, were submitted for molecular tests. PCR amplification and sequencing of als domains demonstrated numerous single nucleotide polymorphisms. Nine biotypes showed non-synonymous substitutions in codon Pro197, changing it to Ser or Thr. Mutation in Pro197 conferred a high level of resistance to the tested herbicides. Analysis of four biotypes also revealed a substitution in the Ala122 codon, changing it to Val. In one biotype this substitution was not accompanied by Pro197 mutation and this biotype was resistant to chlorsulfuron and mesosulfuron + iodosulfuron, but not to sulfosulfuron or propoxycarbazone-sodium. Correspondence between mutations and levels of resistan ce to ALS inhibitors may support management of resistant weeds with the existing palette of herbicides.

Cornflower (Centaurea cyanus L.), one of the main weeds found among winter crops in Poland, has developed herbicide resistance (HR) to acetolactate synthase (ALS) herbicides, a finding first reported in 2006, and in recent years, farmers have been complaining about inadequate chemical control of this weed. This study aimed to characterise the current state of cornflower HR to ALS inhibitors and synthetic auxins in Poland and the agricultural practices in fields with herbicide-resistant populations. From 2017 to 2020, 159 seed samples together with the field history were collected across the country and biological tests performed in glasshouses. This revealed that 47 populations of C. cyanus were cross-resistant to both tribenuron and florasulam, 28 and 8 populations were single resistant to tribenuron and florasulam, respectively, and 3 populations had developed multiple resistance to both ALS inhibitors and synthetic auxins, i.e., 2,4-D and dicamba. Resistant populations were found mostly frequent in northern Poland, but also in the eastern and western parts of the country. Based on a survey of farmers, the resistant populations were found in winter crops regardless of the tillage system (77% of fields with HR cornflower were mouldboard ploughed). Based on the proposed population treatment (PT) index showing the frequency of herbicide use during three consecutive seasons on farms with HR cornflower, the average PT for all the surveyed farms was 5.4. The highest PT of 7.4 was found in the province of Warmia-Masuria in northern Poland.

Abstract:Blackgrass biotype resistant to the mesosulfuron + iodosulfuron mixture has been found in Poland and was investigated in this study. Seedlings that survived double-dosed herbicide treatment were submitted to molecular analysis in order to explain the mechanism of resistance. Domains A and B of the acetolactate synthase gene were amplified by PCR and then sequenced. Biotypes which were both resistant and susceptible to mesosulfuron+iodosulfuron were analyzed. The comparison of the obtained sequences was made on a nucleotide and aminoacid level. The comparison revealed a substitution of proline codon to histidine codon in position 197 in each resistant plant. Mutation Pro197His is the basis of the target site resistance of A. myosuroides to sulfonylureas. There were no other mutations in als gene of the biotype that might modify the level of resistance to these herbicides.