Glyphosate resistance reduces kochia fitness: Comparison of segregating resistant and susceptible F2 populations.

Citation

Martin, S.L., Benedict, L., Sauder, C.A., Wei, W., deCosta, L.O., Hall, L.M., and Beckie, H.J. (2016 to be submitted). "Glyphosate resistance reduces kochia fitness: Comparison of segregating resistant and susceptible F2 populations.", Planta.

Plain language summary

Glyphosate is considered the world’s most important herbicide, but widespread and continual use has resulted in the evolution of resistance. Kochia scoparia (kochia) has evolved resistance by duplicating the gene that produces the protein that is the target of glyphosate. This trait is inherited in a predictable Mendelian manner. Resistant populations have been reported for the Canadian Prairies. Here, we evaluated the whether glyphosate resistance has a cost to the plants – does it reduce the number of offspring the plant can produce - by comparing susceptible and resistant full siblings generated from within six populations. Under competitive greenhouse conditions, whether or not the maternal plants were glyphosate resistant showed persistent effects: delayed emergence, delayed flowering, and reductions in viable seed count and seed weight overall. Glyphosate resistance within a plant resulted in reduced seed count and weight, reduced competitive ability, reduced growth rate in mixed stands, but better germination of the F3. However, all characteristics were highly variable and fitness costs were not constant across all populations. In the absence of selection from glyphosate, kochia with glyphosate resistance will be at a competitive disadvantage in some populations.

Abstract

Glyphosate is considered the world’s most important herbicide, but widespread and continual use has resulted in the evolution of resistance. Kochia scoparia (kochia) evolved resistance via tandem gene amplification of glyphosate’s target, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) and resistant populations have been reported for the Canadian Prairies and the Northern Great Plains. Here, we evaluated the fitness costs of EPSPS amplification in kochia by comparing susceptible and resistant full siblings from segregating F2 populations generated from within six populations. Kochia was expected to be highly diverse because of strong gene flow; however, six of the seven field-collected parents with higher EPSPS copy number were homozygous. Under competitive greenhouse conditions, the EPSPS type of the line’s maternal plant showed persistent effects: delayed emergence, delayed flowering, and reductions in viable seed count and seed weight overall. High EPSPS copy number individuals had reduced seed count and weight, reduced competitive ability, reduced growth rate in mixed stands, but better germination of the F3. However, all characteristics were highly variable and fitness costs were not constant across different genetic backgrounds. In the absence of selection from glyphosate, kochia with increased EPSPS copy number will be at a competitive disadvantage in some genetic backgrounds.

Publication date

2017-05-13

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