Occurrence, resistance factors and cross-resistance patterns to herbicides inhibiting acetolactate synthase (ALS) of Echinochloa crus-galli (L.) Pal. Beauv. in Central Europe

Echinochloa crus-galli (L.) Pal. Beauv. is one of the most noxious weeds in maize cultivation and has evolved target-site resistance to ALS-inhibiting herbicides. Due to the hexaploid nature of E. crus-galli, resistance inducing mutations can be harbored by multiple gene copies, but up to now, studies did not include an analysis of the ALS gene copies conferring resistance. Investigations on E. crus-galli populations from different countries in Central Europe revealed the presence of several point mutations conferring resistance and occurring independently at the positions Ala-122, Pro-197 and Trp-574. Moreover, an Asp-376-Glu mutation in the ALS gene in E. crus-galli and a Ser-653-Tyr amino acid change in the ALS protein of a weed were detected for the first time. Additionally, the study revealed the first case of an ALS-resistant population (Trp-574-Leu) in the Czech Republic. The detection of mutations is relevant to the evolution and management of herbicide resistance. Dose–response experiments showed different effects depending on the population and the individual active ingredients and mixtures. Due to the genetic variability of E. crus-galli, results were highly variable. Overall, the populations showed a high level of resistance. For the prevailing mutated positions, i.e., Ala-122, Pro-197 and Trp-574, gene copies were examined separately using molecular genetic methods. A single mutation in at least one out of three ALS gene copies was sufficient to confer resistance at the positions Pro-197 and Trp-574. At Ala-122, point mutations co-occurring in the ALS 1, ALS 2 and ALS 3 gene copy were identified. The study provides a starting point for differentiation of the resistance mechanisms in polyploid E. crus-galli.