lecture 18

Question 1

herbicide resistance definition

Answer 1

Inherited ability of a plant to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type

Question 2

herbicide tolerance definition

Answer 2

the inherent ability of a species to survive herbicide treatment

Question 3

evolutionary resistance definition

Answer 3

the process where rare resistant individuals become the majority

Question 4

needs for herbicide resistance

Answer 4

• a population of weeds (originally suspectable)
  -genetic change - heritable mutation
• time
  -dose dependance - dose must kill wild type normally

Question 5

two reasons resistance occurs

Answer 5

1) heritable variation (mutation)
2)selection

Question 6

unsatisfactory pesticide performance - not due to resistance

Answer 6

-misapplication
-hard/dirt water
-rainfall following application
-too hot/cold/wet/dry

Question 7

are resistant plants always easy to identify?

Answer 7

no, they may still look like they’re dying but the new growth point is not dying.

Question 8

3 genetic factors influencing evolution of resistance in weeds

Answer 8

1) initial mutation frequency
2)number of genes / mode of inheritance
3)relative fitness

Question 9

2 biological/ecological factors influencing evolution of resistance

Answer 9

1) weed mating system
2) soil seed reserve

(gene flow)

Question 10

2 operational factors influencing evolutionary of resistance

Answer 10

1) selection pressure
2) herbicide use patterns (rotations and mixtures)

Question 11

mutation rates influenced by:

Answer 11

numerous factors and vary considerably among gene loci

Question 12

cytoplasmic vs nuclear inheritance

Answer 12

• triazine resistance - cytoplasmic (chloroplast)

all others - nuclear

Question 13

single gene vs polygenic inheritance

Answer 13

alopecurus myosuroides - 2 additive genes

avena fatua - 2 recessive genes

most others (to date) single gene per MOA

Question 14

recessive vs dominant

Answer 14

most dominant or partially dominant

Question 15

outcrossing effect on resistance

Answer 15

increases spread of resistance through pollen flow

Question 16

low seedbank longevity increases or decreases rate of resistance

Answer 16

increases

Question 17

selection pressure

Answer 17

the more effective the herbicide the more intense the selection pressure

Question 18

4 herbicide attributes causing resistance

Answer 18

high efficacy
frequent, repeated application
soil residual activity
single target site

Question 19

3 main risk factors for evolution of herbicide resistant weeds

Answer 19

1) repeated application of highly efficacious herbicides with the same site of action

2) annual weed species that occur at high population densities, are widely distributed, are genetically variable, are prolific seed producers, have efficient gene dissemination.

3) simple cropping systems that favor a few dominant weed species

Question 20

mechanisms of resistance

Answer 20

altered target site

enhanced detoxification/metabolism

reduced translocation

altered target enzyme specific activity

sequestration

reduced entry

rapid necrosis

Question 21

3 classifications of resistance

Answer 21

1) Resistance -
2) cross resistant -
3) multiple resistant -

Question 22

Cross resistance

Answer 22

evolved mechanism to survive application of more than one class of herbicide

Question 23

multiple resistance

Answer 23

more than one evolved mechanism that provides a broad range of resistance or survival of more than one group of herbicide

Question 24

two ways to slow rate of resistance

Answer 24

1) reduce number of herbicide applications

2)alter MOA’s

Question 25

slowing resistance most effective when:

Answer 25

mechanism conferring resistance is target site based

weds are self pollinated

seed spread is restricted

Question 26

6 steps to identify resistance in a field

Answer 26

1) rule out adverse weather or application errors

2) field records indicate repeated use of the same herbicide

3) weed species now escaping control was well-controlled by the same herbicide

4)escapes cannot be attributed to emergence after application

5)escapes occur in irregular shaped patches

6) collect some mature, dry seed for testing