Abstract
Ecological theory predicts that fitness costs of herbicide resistance should lead to the reduced relative abundance of resistant populations upon the cessation of herbicide use. This greenhouse research investigated the potential fitness costs of two multiple herbicide resistant (MHR) wild oat (Avena fatua) populations, an economically important weed that affects cereal and pulse crop production in the Northern Great Plains of North America. We compared the competitive ability of two MHR and two herbicide susceptible (HS) A. fatua populations along a gradient of biotic and abiotic stresses The biotic stress was imposed by three levels of wheat (Triticum aestivum) competition (0, 4, and 8 individuals pot−1) and an abiotic stress by three nitrogen (N) fertilization rates (0, 50 and 100 kg N ha−1). Data were analyzed with linear mixed-effects models and results showed that the biomass of all A. fatua populations decreased with increasing T. aestivum competition at all N rates. Similarly, A. fatua relative growth rate (RGR) decreased with increasing T. aestivum competition at the medium and high N rates but there was no response with 0 N. There were no differences between the levels of biomass or RGR of HS and MHR populations in response to T. aestivum competition. Overall, the results indicate that MHR does not confer growth-related fitness costs in these A. fatua populations, and that their relative abundance will not be diminished with respect to HS populations in the absence of herbicide treatment.
Highlights
The reliance on herbicides for weed control has posed strong selection pressure for resistant populations, and there are nearly 400 unique cases of herbicide resistance in 217 plant species [1]
The results indicate that multiple herbicide resistant (MHR) does not confer growthrelated fitness costs in these A. fatua populations, and that their relative abundance will not be diminished with respect to herbicide susceptible (HS) populations in the absence of herbicide treatment
At all N rates, the biomass of A. fatua decreased as T. aestivum biomass increased (P,0.05) (Figure 1) while the relative growth rate (RGR) of all A. fatua populations decreased with increasing T. aestivum biomass for the two higher N fertilization rates, but not at the zero N rate (P = 0.213) (Figure 2)
Summary
The reliance on herbicides for weed control has posed strong selection pressure for resistant populations, and there are nearly 400 unique cases (plant species 6site of action) of herbicide resistance in 217 plant species [1]. Herbicide resistant biotypes are predicted to experience a fitness cost as resources are shifted to resistance mechanism(s) rather than to growth and reproduction. Such fitness costs have been associated with a number of specific gene mutations conferring resistance to herbicides (see [9] for a review). Particular target site mutations may or may not be associated with fitness costs in resistant populations
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