Mechanism of resistance to mesotrione in an Amaranthus rudis population from Nebraska

Transcription

1 Mechanism of resistance to mesotrione in an Amaranthus rudis population from Nebraska Shiv Shankhar (Deepak) Kaundun EWRS, Montpellier, June 215

2 Importance of HPPD herbicides in corn agro-systems HPPD herbicides: latest successful herbicide mode of action introduced with market value of over 1.5 billion USD/year Sales dominated by mesotrione, tembotrione, topramezone and isoxaflutole for grass and broad-leaf weed control in US corn agro-systems Compounds efficacious on driver weeds and can be used in mixtures with other herbicides, e.g. photosystem II (synergism) Extensive use has resulted in resistance in a few Amaranthus rudis and Amaranthus palmeri populations from Iowa, Illinois, Kansas and Nebraska 2

3 Evolution of resistance to mesotrione in an Amaranthus rudis population from Platte County, Nebraska, USA Untreated control Mesotrione 15 g ai/ha Field history: soybean (pendimethalin followed by glyphosate) / seed corn (S-MC + atrazine pre-emergence followed by mesotrione + atrazine post-emergence) rotation from

4 bjectives Confirm resistance to mesotrione in a suspected resistant Amaranthus rudis population from Nebraska Establish the cross resistance profiles to other cornselective HPPD herbicides Determine the mechanism(s) of resistance to mesotrione in the Nebraska population 4

5 Materials and methods Plant materials - Suspected resistant A. rudis population from Nebraska (: 21 seed collection) - Standard sensitive population (: Herbiseed, Twyford, UK ) Methods - Glasshouse-based herbicide pot tests - Molecular assays HPPD gene analysis via Sanger sequencing HPPD gene duplication via Q-PCR analyses - Biokinetics assays uptake and translocation - 14 C mesotrione metabolism - non-labelled mesotrione 5

6 % control % control Comparative responses of and to mesotrione Pre-emergence (Rf = 2.4) Post-emergence (Rf = 45.5) Field rate mesotrione g ai/ha Field rate mesotrione g ai/ha Low and high levels of resistance (p<.5) to mesotrione applied pre- and post-emergence respectively in 6

7 % control % control % control % control Resistance profiles to four corn-selective HPPD herbicides 1 Post-emergence - tembotrione 1 Post-emergence - topramezone g ai/ha g ai/ha 1 Post-emergence - sulcotrione 1 Pre-emergence - Isoxaflutole g ai/ha g ai/ha is cross resistant to other corn selective HPPD herbicides 7

8 Target-site-resistance HPPD sequence comparison between and 12 each of survivors and untreated plants sequenced for the whole HPPD gene HPPD gene is 135 bp in length consistent with previously published Amaranthus rudis sequence (GenBank: JX259255) 52 nucleotide changes identified of which 15 were non-synonymous Non-synonymous mutations were evenly distributed between sensitive and resistant plants A target gene mutation is not associated with resistance to mesotrione in 8

9 Relative number of HPPD gene copies Target-site-resistance Relative HPPD gene copy number in and 3 CPS gene used for normalization ALS gene used for normalization 2 1 HPPD gene duplication is not associated with resistance to mesotrione in 9

10 Uptake - % of applied Non-target-site-resistance Mesotrione uptake in and Total 14 C radiochemical recoveries in whole plants Time (h) after treatment 14 C label N + S - No evidence of a difference (p =.689) in uptake between and 1

11 Translocation - % of absorbed Non-target-site-resistance Mesotrione translocation in and 35 Total 14 C radiochemical recoveries outside treated area N C label S Time (h) after treatment Evidence (P=.142) of differential translocation between sensitive and resistant populations 11

12 Mesotrione - % of absorbed Mesotrione - % of absorbed Non-target-site-resistance - metabolism Levels of parent mesotrione (LC-MS) in and Treated area utside treated area Time (h) after treatment Time (h) after treatment Significantly lower levels of parent mesotrione recovered from for at 48 and 72 hours (P<.5) 12

13 4-H mesotrione - % absorbed Non-target-site-resistance - metabolism Levels of 4-hydroxy mesotrione (LC-MS) in and Treated area N H S Time (h) after treatment 4-hydroxymesotrione Significantly higher levels of 4-hydroxy mesotrione recovered from treated area for at 48 and 72 hours (p<.5) 13

14 Conclusions Resistance to a range of corn-selective HPPD herbicides especially applied post-emergence is confirmed in A target gene mutation/duplication or differential uptake is not associated with mesotrione resistance in Resistance in is (in part ) due to higher levels of mesotrione metabolism via 4-hydroxylation Relatively lower levels of translocation observed could be due to higher levels of mesotrione metabolism in 14

15 Acknowledgements Sarah Jane Hutchings Richard Dale Anushka Howell Timea Kokeny Vance Kramer Vinod Shivrain Aaron Franssen Les Glasgow Gordon Vail Eddie Mcindoe 15

16 16 Thank you for your attention.