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Title: Concerted action of target-site mutations and high EPSPS activity in glyphosate-resistant junglerice (Echinochloa colona) from California

Author
item GARCIA, ALEJANDRO - University Of California
item ALARCON-REVERTE, ROCIO - University Of California
item Watson, Susan
item ABDALLAH, IBRAHIM - Cairo University
item Dayan, Franck
item FISCHER, ALBERT - University Of California

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2014
Publication Date: 7/1/2015
Citation: Garcia, A.M., Alarcon-Reverte, R., Watson, S.B., Abdallah, I., Dayan, F.E., Fischer, A. 2015. Concerted action of target-site mutations and high EPSPS activity in glyphosate-resistant junglerice (Echinochloa colona) from California. Pest Management Science. 71:996-1007.

Interpretive Summary: Glyphosate is the most widely used non-selective herbicide and Echinochloa colona is an annual weed affecting field crops and orchards in California. This work characterizes the mechanism of resistance to glyphosate in some population of this important weed species. There was no difference in uptake, translocation or metabolism of the herbicide. However, several molecular events have occurred independently, such as the selection of a proline106 to threonine and proline106 to serine substitutions, as well as a 5-fold increase in the activity of the enzyme targeted by glyphosate. We demonstrate that individuals with different glyphosate resistance mechanisms can coexist in the same population, individuals from different populations may carry different resistance mechanisms, and different mechanisms can act in concert in single E. colona plants.

Technical Abstract: Glyphosate is the most widely used non-selective herbicide and Echinochloa colona is an annual weed affecting field crops and orchards in California. A population carrying a glyphosate-resistance-endowing mutation in the EPSPS gene was found in the Northern Sacramento Valley. We used selfed lines derived from populations collected in glyphosate treated fields to describe additional mechanisms involved in glyphosate resistance. Based on the amount of glyphosate to kill 50% of the plants (LD50), glyphosate-resistant (GR) lines were 4 to 9-fold more resistant than susceptible (S) plants and accumulated less shikimate. GR and S lines did not differ in glyphosate absorption, translocation or metabolism (very limited). Mutations corresponding to Pro106Thr and Pro106Ser substitutions were found in different homologous EPSPS genes. Quantitative RT-PCR on cDNA revealed GR lines had similar or lower EPSPS expression than S plants. A non-mutant line with 1.4-fold greater EPSPS activity was 5-fold more GR than S plants. The effect on whole plant resistance was additive when the different mechanisms accumulated on single GR plants. We demonstrate that Individuals with different glyphosate resistance mechanisms can coexist in the same population, individuals from different populations may carry different resistance mechanisms, and different mechanisms can act in concert in single E. colona plants. However, other plant factors or resistance mechanisms appear to modulate plant expression of EPSPS sensitivity to glyphosate.