2,4-D resistance due to a deletion in IAA2 in Sisymbrium orientale L. carries no apparent fitness penalty.

Background: A deletion mutation in the degron tail of auxin coreceptor IAA2 was found to confer resistance to the herbicide 2,4-D in Sisymbrium orientale. Given the importance of auxin signalling in plant development, this study was conducted to investigate whether this deletion mutation may affect plant fitness.

Results: The F progeny of crosses with two resistant populations P2 (P2♂ × S♀) and P13 (P13♂ × S♀) were used in this study. The F plants were grown under competition with wheat in pot-trials and evaluated for biomass and total seed production. Progeny of the F plants were phenotyped by application of 250 g a.e. ha 2,4-D and genotyped for the 27 bp deletion in IAA2. In a separate experiment, F and F recombinant inbred lines (RILs) with resistant and susceptible phenotypes were grown in monoculture and phenotyped over time for biomass and seed production. Wheat competition reduced biomass and seed production for all genotypes in each population and in each year. A density of 400 plants m of wheat reduced Sisymbrium orientale biomass by 76-78% in 2016 and by 59-63% in 2017 and total seed production by 80-83% and 60-64% by respective year. For the experiment involving resistant and susceptible RILs, biomass accumulation and seed production were the same between resistant and susceptible for both populations.

Conclusions: The 27 bp deletion in IAA2 in Sisymbrium orientale does not carry a measurable fitness penalty, as determined by biomass reduction or seed production, either in monoculture or in competition with wheat. As a result, this mutation is unlikely to decrease over time in weed populations if 2,4-D selection pressure were removed. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.