EPSPS duplication and mutation involved in glyphosate resistance in the allotetraploid weed species Poa annua L.

Abstract

BACKGROUND Poa annua is a widespread winter annual weed species in California. Recently, poor control of this species with glyphosate was reported by growers in an almond orchard in California with a history of repetitive glyphosate use. The objectives of this research were to evaluate the level of glyphosate resistance in a developed S4 P. annua line (R) and identify the mechanisms of resistance involved. RESULTS Whole‐plant dose–response experiments confirmed glyphosate resistance in R, which required 18‐fold more glyphosate to achieve a 50% growth reduction compared with a susceptible line (S), results that were supported by the lower shikimate accumulation observed in R compared with S. No differences in glyphosate absorption, translocation, or metabolism were observed, suggesting that non‐target‐site mechanisms of resistance are not involved in the resistance phenotype. A missense single nucleotide polymorphism was observed in EPSPS coding position 106 in R, resulting in a leucine to proline substitution. This polymorphism was observed exclusively in P. supina EPSPS homeologs. A seven‐fold increase in the number of copies of EPSPS alleles was observed in R compared with S. CONCLUSIONS We report the first case of glyphosate resistance associated with both EPSPS duplication and target‐site mutation at position 106, leading to high levels of glyphosate resistance in the allotetraploid weed species Poa annua L. Data obtained in this research will be useful for the development of diagnostic tools for rapid glyphosate resistance identification, monitoring and containment. © 2018 Society of Chemical Industry

Mechanisms of evolved herbicide resistance

“…More recently, an allotetraploid P. annua population was identified with resistance to glyphosate via a Pro106Leu mutation in EPSPS and 7-fold increased EPSPS copy number (185). Interestingly, both the target site mutation and duplicated EPSPS genes were present in homoeologs only from the supine bluegrass (Poa supina) progenitor sub-genome.…”

Evidence of multiple origins of glyphosate resistance evolution in Lolium multiflorum

“…In addition, resistant Kochia scoparia plants had up to 10 copies of the gene (Gaines et al, 2016), likely mediated by a mobile genetic element (Patterson et al, 2019). Lastly, EPSPS duplication associated with a nonsense mutation in the EPSPS gene has been observed in the allotetraploid grass species Poa annua (Brunharo et al, 2018).…”

A holistic approach in herbicide resistance research and management: from resistance detection to sustainable weed control

“…In another population of A. palmeri from Cordoba province, resistance to glyphosate was exclusively endowed by NTSR of reduced absorption and impaired translocation 21 . Examples in other weed species include a glyphosate-resistant Poa annua population from the USA [resistance index (RI) = 17.9], where a sevenfold EPSPS gene copy number and a weak P106L mutation coexist, with dominant contribution from gene duplication 22 ; and more recently, a glyphosate-resistant Eleusine indica population from China (RI = 13.4), where a P106A mutation and a low level of gene duplication/overexpression coexist, with dominant contribution from the TS mutation 23 . In some occasions of resistance to herbicides of other modes of action, such as diclofop-methyl (acetyl-CoA carboxylase inhibitor) and metribuzin (photosystem II inhibitor), TS mutation and NTSR mechanisms had concurrently strong contributions 24 , 25 .…”