Regional diversity of the ALS gene and hormesis due to tribenuron-methyl in Centaurea cyanus L.

Centaurea cyanus L. is a common field weed in Eastern Europe but only in Poland biotypes of this species with resistance to acetolactate synthase (ALS) inhibitors have been confirmed. This phenomenon is constantly developing and spreading to consecutive regions of Poland. This study aimed to assess the response of selected Polish C. cyanus populations to tribenuron-methyl and to analyse the genetic variability of the ALS gene of C. cyanus populations resistant to ALS inhibitors. Between 2017 and 2021, 13 seed samples were collected from eastern Poland and a dose-response study with tribenuron-methyl was performed. Eleven populations resistant to tribenuron-methyl were identified. All populations from this study as well as 6 additional resistant populations characterised in the previous dose-response studies were subjected to molecular analysis of the ALS gene. Target-site resistance due to mutations P197S, P197Q, P197T and P197A were identified in 8 populations from Warmia-Masuria and Podlaskie provinces. This is the first case of target-site resistance (TSR) in C. cyanus confirmed by sequencing of the ALS gene. Moreover in some resistant plants, ten changes in the amino acid ALS sequence were identified in comparison to those in the susceptible ones. In none of the populations were all mutations detected in the same individual. The highest frequency of mutations was detected in Warmia-Masuria province. Some C. cyanus populations resistant to ALS inhibitors showed hormesis effect concerning shoot fresh weight after tribenuron-methyl treatment. Stimulation due to half the recommended dose of tribenuron-methyl was the highest and the difference between untreated and treated plants was statistically significant in two populations from Warmia-Masuria and in one from Podlaskie province.