Glyphosate-Resistant Kochia (Kochia scoparia) in Kansas: EPSPS Gene Copy Number in Relation to Resistance Levels

Abstract

Reports of kochia control failure with glyphosate in western Kansas increased dramatically in the years following confirmed presence of glyphosate-resistant (GR) populations in 2007. In this study, progeny from 8 of 16 geographically dispersed kochia populations in western Kansas (seed collected in 2010) were confirmed to be resistant to glyphosate by conducting whole-plant dose-response (in greenhouse and/or outdoor environments) and shikimate-accumulation assays. Additionally, the relationship between 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene copy number and glyphosate resistance levels was investigated. A known glyphosate-susceptible (GS) kochia population from Ellis County, Kansas was used for comparison in all studies. Based on the herbicide rate that caused 50% reduction in biomass compared to untreated control (GR50) values, the 8 GR kochia populations were 4 to 11 times more resistant to glyphosate compared to the GS population. The GR50values of kochia populations were 1.58 to 1.85 times higher under an outdoor environment compared to when grown in the greenhouse. Glyphosate-treated leaf discs of the GS kochia plants accumulated consistently higher amounts of shikimate than those of the GR plants. Additionally, the GR plants with higher levels of resistance to glyphosate had higher EPSPS : acetolactate synthase (ALS) relative gene copy number compared to those with low levels of resistance.

Field‐evolved resistance to four modes of action of herbicides in a single kochia (Kochia scoparia L. Schrad.) population

“…This mechanism of resistance has been reported in several other glyphosate-resistant kochia populations in the Central Great Plains of the United States. 9,13,21 In the present study, 90% of the GC population survived the labeled rate of dicamba. Recently, Crespo et al 22 found that greater than 560 g a.e.…”

“…Similar levels of resistance have been reported in other glyphosate-resistant kochia populations from the region. 9 The EPSPS gene copy number was measured relative to an ALS gene in five plants of GC kochia. Increased EPSPS gene copy numbers ranging from 5 to 9 were observed in GC plants, suggesting gene amplification as a contributing mechanism to glyphosate resistance (Fig.…”

“…Recently, several populations of kochia were also confirmed as being resistant to glyphosate. 9 Nonetheless, evolved resistance to these four herbicides in a single population has not been reported.…”

EPSPS Gene Copy Number and Whole-Plant Glyphosate Resistance Level in Kochia scoparia

“…Increased EPSPS gene copy number and expression has been shown to be a mechanism for glyphosate-resistance in K . scoparia collected from Kansas [14]; Colorado, North Dakota, and South Dakota [8]; and Montana [15]. Detection of EPSPS genes on distal ends of homologous chromosomes suggests that increase in EPSPS gene copies in GR K .…”

“…scoparia populations from Kansas, EPSPS gene copy number was correlated to resistance level, such that within a resistant K . scoparia population, individuals with higher EPSPS copy number displayed less injury symptoms compared to individuals with lower EPSPS copy number [14]. …”