Abstract
The alleles responsible for herbicide resistance in weeds can result in a fitness cost within affected plants. Over 200 cases of resistance to triazine herbicides have been confirmed in a wide range of weed species globally. In New Zealand, Chenopodium album L. was the first species reported as resistant to triazines. Several studies have already shown that triazine resistance in weeds is associated with fitness costs. Our current study provides further information about fitness penalties caused by triazine resistance during the vegetative growth phase of C. album. Triazine-resistant phenotypes produced less biomass and were shorter than susceptible ones prior to the onset of flowering. At an early stage of growth, triazine-resistant plants had lower photosynthetic efficacy and growth rates than susceptible plants, indicated by lower net assimilation rate (NAR) and relative growth rate (RGR), respectively. However, at a later stage of growth, the resistant plants had greater RGR values than susceptible phenotypes, though there were no significant differences in NAR between triazine-resistant and susceptible plants at this later stage. The triazine-resistant plants had less capacity for vegetative growth than susceptible plants during competition with wheat, indicating less ability to capture resources by triazine-resistant plants under competition. Overall, this study has revealed that the triazine resistance allele caused a substantial fitness cost to C. album only at the early phase of vegetative growth stage; thus, the use of crop competition to try managing triazine-resistant C. album plants should occur during this early phase.
Highlights
Triazines are broad-spectrum herbicides that target the plastoquinone B (PQB) binding site located on the photosystem II D1 protein [1]
The fitness penalty associated with pesticide resistance can influence the process of resistance allele stabilization and the dynamics of the pesticide resistance evolution in a population [12]
This research showed that triazine-resistance in C. album results in some fitness costs which cause lower vegetative growth rates, reductions in leaf area and smaller plant size at the early vegetative phase
Summary
Triazines are broad-spectrum herbicides that target the plastoquinone B (PQB) binding site located on the photosystem II D1 protein [1]. The first case of resistance to triazines in weeds was reported in the early 1970s in Senecio vulgaris L. [3], and far, over 200 cases of resistance to triazines in a wide range of weed species have been reported globally [4]. An altered target site owing to a mutation in the photosystem II protein D1 (psbA) gene is the most typical triazine-resistance mechanism in weed species studied to date [5]. There are a few cases of resistance in which a non-target site resistance mechanism, enhanced herbicide detoxification [6], has been reported as the mechanism of resistance to triazines in Abutilon theophrasti. The cost associated with the resistance mutation(s) in the absence of a Agronomy 2019, 9, 523; doi:10.3390/agronomy9090523 www.mdpi.com/journal/agronomy
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