Dücker, Rebecka

English

This study aimed to elucidate the resistance mechanisms behind flufenacet resistance in
Alopecurus myosuroides and Lolium spp. field populations. In a first step field populations
of both species were screened in greenhouse bioassays and suitable biological material
was selected for the investigation of the further studies using analytical and biochemical
techniques as well as an RNA-Seq approach.
In a screening with 50 A. myosuroides populations shifts in efficacy with resistance factors
up to 7 were estimated and six populations from the Northern German Marshes were
controlled by less than 90% with the field rate registered in Europe. The efficacy of several
pre-emergence herbicides of different modes of action on sensitive populations and
Northern German A. myosuroides populations with shift in flufenacet sensitivity was
explored. While none of the herbicides registered in Europe were more effective on those
populations than flufenacet, it was shown that particularly three-way-mixtures including
flufenacet and the PDS inhibitor diflufenican increased the control of those populations
significantly. The observed shift in flufenacet efficacy in A. myosuroides populations was
comparably low, whereas resistance factors up to 61 were observed in a screening with 22
Lolium spp. field populations. For the first time, field relevant levels of flufenacet resistance
were described in Lolium populations from France and the United Kingdom, but also in
populations from the USA and the commercially available population VLR69 originating
from Australia.
The level of resistance correlated in case of both, A. myosuroides and Lolium populations
with flufenacet degradation rates determined by HPLC. Similar detoxification pathways with
glutathione conjugation as a first rate-limiting step were elaborated for both species based
on metabolites identified by LC-MS/MS. The pathways suggest enhanced glutathione
transferase activity as a main driver of the resistance observed in both species tested.
The large differences in flufenacet resistance observed in Lolium population allowed the
selection of biological material for an RNA-Seq study. By differential gene expression
analysis of the transcriptomes of three sensitive and three flufenacet resistant Lolium
populations, 11 differentially upregulated GSTs were identified. These findings were
validated with four recombinant GST isoforms in vitro. The ability to detoxify flufenacet was
confirmed with one tau class GST showing a high flufenacet turnover rate and one phi class
GST with high sequence similarity to LrGSTF1 and a lower flufenacet turnover rate. These
results suggest that flufenacet resistance in Lolium populations is caused by upregulation
of at least one GST with high substrate-specificity to flufenacet in combination with a
cumulative effect with at least one other GST with lower substrate-specificity to flufenacet.
84
Finally, none of the recombinant enzymes were able to degrade diflufenican and the ALS
inhibitor mesosulfuron-methyl, suggesting that these herbicides are suitable for a
combination with flufenacet in resistance management program, as no cross-resistance
between these herbicides is expected

Georg-August-University Göttingen

Molecular Mechanisms of Flufenacet Resistance in Grass Weeds

https://ediss.uni-goettingen.de/bitstream/21.11130/00-1735-0000-0005-12E5-4/2/Merged_Diss_2010_Duecker.pdf

Molecular Mechanisms of Flufenacet Resistance in Grass Weeds

Abstract

Similar works

Full text

Available Versions

Georg-August-University Göttingen