Investigating the presence of compensatory evolution in dicamba resistant IAA16 mutated kochia (Bassia scoparia)^†

Abstract

BACKGROUND Lack of fitness costs has been reported for multiple herbicide resistance traits, but the underlying evolutionary mechanisms are not well understood. Compensatory evolution that ameliorates resistance costs, has been documented in bacteria and insects but rarely studied in weeds. Dicamba resistant IAA16 (G73N) mutated kochia was previously found to have high fecundity in the absence of competition, regardless of significant vegetative growth defects. To understand if costs of dicamba resistance can be compensated through traits promoting reproductive success in kochia, we thoroughly characterized the reproductive growth and development of different G73N kochia biotypes. Flowering phenology, seed production and reproductive allocation were quantified through greenhouse studies, floral (stigma‐anthers distance) and seed morphology, as well as resulting mating and seed dispersal systems were studied through time‐course microcopy images. RESULTS G73N covaried with multiple phenological, morphological and ecological traits that improve reproductive fitness: (i) 16–60% higher reproductive allocation; (ii) longer reproduction phase through early flowering (2–7 days); (iii) smaller stigma‐anthers separation (up to 60% reduction of herkogamy and dichogamy) that can potentially promote selfing and reproductive assurance; (iv) ‘winged’ seeds with 30–70% longer sepals that facilitate long‐distance seed dispersal. CONCLUSION The current study demonstrates that costs of herbicide resistance can be ameliorated through coevolution of other fitness penalty alleviating traits. As illustrated in a hypothetical model, the evolution of herbicide resistance is an ongoing fitness maximization process, which poses challenges to contain the spread of resistance. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Herbicide diagnostics reveal multiple patterns of synthetic auxin resistance in kochia (Bassia scoparia)

“…Subsequent research identified significant impairment of vegetative growth in segregating lines of the Nebraska G73N accession, which manifest as reduced plant height, thicker leaf blades with lower photosynthetic efficiency, reduced stem diameter with less developed vascular bundle systems, impaired plant competitiveness, and lower biomass (LeClere et al 2018;Wu et al 2021b). Despite these vegetative defects, the G73N mutation was associated with higher reproductive allocation, an earlier yet extended flowering window, reduced stigma-anther distance potentially aiding in self-pollination and reproductive assurance, and winged seeds that could facilitate long-distance dispersal (Wu et al 2021a). It is yet unclear whether these fitness penalties and resulting compensatory evolution of traits aiding in reproductive assurance are associated with other mechanisms that confer synthetic auxin resistance in kochia.…”