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Information and Results
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Kochia was introduced to North America from Europe and has become a troublesome weed in both cropland and non-cropland as well as in arid and semi-arid regions of the western United States and Canada. Kochia is highly adaptive and grows on many soils including saline and alkaline soils. No-till crop production systems favor infestation of kochia. Kochia infests about two-thirds of the crop fields in western Kansas and the infestation has increased by 50% in the past 5-6 years. Because of continuous use of glyphosate in no-till system, several populations of kochia evolved resistance to this herbicide. Glyphosate- resistant kochia populations survived multiple applications of glyphosate in an irrigated glyphosate-resistant soybean field near Colby, KS.
Herbicide resistance essentially is an inevitable consequence of the use of herbicides as a primary weed control strategy. Thus, the overall goal of the proposed research is to better predict and manage glyphosate resistance in kochia by understanding the genetic basis; specifically, the inheritance of glyphosate resistance in this weed.
As glyphosate is widely used in soybean production and kochia (K. scoparia) is a problem weed of Kansas, understanding the genetic basis of glyphosate resistance in kochia will help determine the rate of spread of this resistance in new populations; thereby, proactive management practices can be implemented to reduce the spread of the resistance. Towards this end, this research will determine the genetic basis of resistance using glyphosate-resistant and -susceptible kochia populations from Kansas.
1. Identify homozygous glyphosate-resistant and -susceptible accessions from individually self-pollinated kochia plants.
2. Perform reciprocal crosses between homozygous glyphosate-resistant and ?susceptible plants to generate F1 and F2 progeny.
3. Determine the response of these progeny to glyphosate.
4. Quantify shikimate levels and 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene copy number in parental, F1, and F2 progeny expressing glyphosate resistance or susceptibility.
Progress of Work
Final Project Results
The results suggest that the F1 plants from reciprocal crosses were all resistant to glyphosate suggesting that the glyphosate resistance is a nuclear trait in kochia. Furthermore, florescent in situ hybridization analysis was performed on glyphosate-resistant and –susceptible kochia chromosomes. The results indicate for the first time that the EPSPS copies are arranged in tandem and are located close to the telomere region of the chromosomes. These results suggest that the EPSPS amplification may have occurred as a result of unequal recombination. We have also tested kochia populations from Kansas for multiple herbicide resistance. The results suggest that these populations are at least resistant to more than 2 modes of action of herbicides. Multiple herbicide resistant kochia is a major challenge for kochia management.
Benefit to Soybean Farmers