Defense Mechanism. Linda Hall

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1 Defense Mechanism s Linda Hall University o f Alberta

2 Weed defend themselves from control measures in many ways

3 Natural selection to avoid control measures Avoidance Tolerance Delay of emergence Plasticity Winter annual cleavers

4 Stork s Bill Erodium cicutarium

5 Two types of defense mechanisms against herbicides TSR Target Site Resistance NTSR Non- Target Site Resistance

6 What is a target site? SpeciEic place in the plant where the herbicide binds and eventually kills the plant Herbicides are grouped by target site Products by the number ACCase ALS Auxinic Herbicides with the same target site interact with the same process, the same enzyme in plants Symptoms look the same Similar timing for activity Similar toxicology Similar application parameters

7 Two types of defense mechanisms against chemicals TSR Target Site Resistance NTSR Non- Target Site Resistance

8 TSR Target Site Resistance

9 TSR Target Site Resistance Only is effective on herbicides that Eit into the same target site (same site of action) Relatively quick to select for NTSR Non- Target Site Resistance Common for some herbicide groups

10 Examples of TSR Point mutations are common and enough to change herbicide binding to target site Changes to the Group 2 ALS enzyme that confer resistance in Kochia Spiny annual sowthistle Cleavers Chickweed Stinkweed Wild oat

11 Seven different mutations of Group 1 ACCase to confer resistance in wild oat Population Individual Position Kelvington 1-6 X Lethbridge 1, 3-6 X 2 X Birch Hills X Beckie, H.J., Warwick, S.I. and Sauder, C.A., Basis for herbicide resistance in Canadian populations of wild oat (Avena fatua). Weed science 6:10-18.

12 Position = resistance and cross resistance Population Individual Position FOP H L H H L FEN L DIm H L H H H H H DEN H H L L L L L Kelvington 1-6 X Lethbridge 1, 3-6 X 2 X Birch Hills X

13 TSR Target Site Resistance Relatively quick to select and common for some herbicides Not universal can vary between herbicides in the same mode of action Cross resistant is predictable with DNA testing Changing herbicide groups is a common solution High or low rates of herbicide select for TSR quizalofop NTSR Non- Target Site Resistance Group 1 ACCase inhibitors FOPs DIMS clodinafop DENs

14 Target Site AmpliEication

15 Kochia resistance to glyphosate Target site of glyphosate is an enzyme EPSPS During pollen and ovule production genes are duplicated and crossing over occurs Sometimes crossing over is not even Genes at the end of the chromosome are duplicated EPSPS copy number increases Susceptible has 2 copies of EPSPS Resistant has three copies

16 Resistant increases with increased copy number

17 TSR Target Site Resistance Only is effective on herbicides that Eit into the same target site (same mode of action) Gene amplieication is rarer NTSR Non- Target Site Resistance Creeping resistance First (lower #) copies can be controlled but Lower copy number may reproduce if sprayed late, at low rates, in windy conditions Low herbicide rates may select for gene amplieication

18 Non- Target Site Resistance GST Enhanced growth Phoenix Cytochrome P450

19 Endogenous super families of enzymes sugar GST P450 Cytochrome P450 Vacuole R- X GST R- GT

20 Enhanced herbicide metabolism GST Cytochrome P450 Group 1, 2 clodinafop quizalofop Crops use the same endogenous enzymes as crops to metabolize herbicides Several herbicide groups are degraded using the same mechanism resistance to herbicides in several different groups Only effective on selective herbicides that can be metabolized No simple genetic test imazamox

21 TSR Target Site Resistance NTSR Non- Target Site Resistance Enhanced metabolism Resistance to herbicides in multiple groups More than one genetic change Additive Super families difeicult to formulate a rapid screen Low herbicide rates select for NTSR

22 Enhanced seedling growth Enhanced growth Wild oat resistant to triallate and difenzoquat soil applied herbicides Seedlings growth through the herbicide Groups 8 resistance is still present in much of western Canada

23 Resistance to soil applied herbicides in wild oat Pre- existing cross- resistance Triallate resistant wild oat are resistant to pyroxasulfone (Group 15) and sulfentrazone (Group 14) Resistance to herbicides that were never applied to these populations Amy Mangin, Linda M. Hall, Hugh J. Beckie,

24 NTSR The phoenix resistance to glyphosate in The Phoenix

25 GR resistant giant ragweed At the earliest assessment, giant ragweed injury due to glyphosate treatment was rapid necrosis of the mature leaf tissue, as well as slight chlorosis of the newest leaves.

26 TSR Target Site Resistance Resistance to a single group Variable cross resistance NTSR Non- Target Site Resistance Resistance to herbicides in multiple groups

27 Pollination Defence

28 TSR Target Site Resistance Non- Target Site Resistance Stacking of resistance gene (multiple herbicide resistance) TSR AND NTSR are the norm in many species including wild oat and kochia Several mutations for one target site A mutation at more than one target site TSR and NTSR Resistance testing now becomes very difdicult

29 Dispersal Defense

30 You may not get the weeds you deserve Short distance movement Pollen from plant to plant 1 to 100 s meters Short distance seed dispersal Long distance movement Kochia Spiny annual sowthistle Conyza,

31 Canada fleabane Conyza canadensis

32 Shields, Elson J., Joseph T. Dauer, Mark J. VanGessel, and Gabor Neumann.

33 IWM Incredible IWM Waste of Mytime Incredible Waste of Mytime

34 Playbook for herbicide resistance Spray only one herbicide group or (even better) Spray one herbicide Grow the same monoculture year after year Spray a lot of weeds to increase your odds Residual herbicides are great! Save money! Cut your seeding rates and say yes to brown bag seed Invite the neighbors for a combine party To increase your changes for TSR Do not use herbicide mixtures To increase your changes of gene amplieication TSR or metabolic NTSR, Spray at low rates Spray big, healthy weeds Spray late Use low water volumes

35 Fast as a speeding bullet? All kochia is resistant to ALS inhibitors Eirst identieied in 1988? When will it all be glyphosate resistant? Most wild oat resistant to Group 1 and 2 (ALS and ACCase inhibitors) > 50% of samples Susceptible spiny annual sowthisle - Anyone see one lately? Resistant surveys are critical to track changes Better, faster diagnostic services

36 Waiting for a super hero? The next glyphosate is not coming to save you Sorry

37 More research focus on non- herbicidal controls