Ecological fitness cost associated with the AHAS Trp574Leu mutation in feral Raphanus sativus

Abstract

Gene mutations endowing herbicide resistance may have negative pleiotropic effects on plant fitness. Quantifying these effects is critical for predicting the evolution of herbicide resistance and developing management strategies for herbicide-resistant weeds. This study reports the effects of the acetohydroxyacid synthase (AHAS) Trp574Leu mutation throughout the life cycle of feral radish (Raphanus sativus L.). Resistant and susceptible phenotypes responded differently to light and water treatments in relation to germination and emergence. Under light exposure, the resistant phenotype showed higher germination and emergence, but no differences were found in seed dormancy, germination in darkness and emergence from buried seeds or pods. The resistant phenotype showed delayed and reduced seedling emergence relative to the susceptible phenotype under rainfed conditions, but these differences between the phenotypes were not detected in irrigated soil. The phenotypes showed similar relative growth rates and vegetative biomass. However, under wheat competition, resistant plants had 36%–46% less total above-ground biomass, 26%–47% less seeds per plant and 36%–53% less plant yield than susceptible ones, and these differences were more evident at higher plant density. This study provides a better understanding of the ecological fitness cost associated with the AHAS Trp574Leu mutation in feral R. sativus. The fitness costs could reduce the frequency of the resistant allele in areas untreated with AHAS-inhibiting herbicides. Our results suggest that incorporating non-AHAS herbicidal approaches into integrated weed-management programmes and maintaining fence lines and fields margin as refuges of susceptible plants provides an opportunity to minimize or reverse herbicide resistance evolution.