Lecture 8: GM & crop protection: Herbicide tolerance Flashcards
Threats to crop productivity:
-Weeds
-Pests
-Disease
Adverse environmental conditions (drought, frost & salinity)
By far the majority of GM crops approved for use have been…
crop protection applications
method behind herbicide tolerance, why do we make them
- create transgenic crops resistant to common herbicides
- fields cane sprayed with herbicide when the crop is growing
- weeds killed but crop unaffected
benefits to HT (herbicide tolerance)
- easy for farmers to manage weed problems
- a great commercial opportunity for the Agro companies that can sell both the Ht and the herbicide as a package
Ht can be used alongside ____ to become ‘stacked’
alongside Bt - Bacillus thuringiensis toxin (insect tolerance)
Multiple Ht or Bt genes may be incorporated into on crop
-majority of GM maize and cotton are ‘stacked’
Uptake of Bt maize in the Eu (Spain)
- Bt farmers sprayed significantly less insecticide than conventional farmers
- profit per hectare was increased
- 5% of the total acreage in 1998 now 30%
uptake of adoption of genetically engineered crops in US is
HUGE
-to be adopted so quickly by farmers must get really quick & good response
EU vs USA uptake of Bt maize (& really general)
- Virtually no adoption in EU apart from Spain
- EU trials peaked in 1997 & now dropped - due to EU views
what plant processes do herbicides affect:
- light processes
- cell metabolism
- growth cell division
Are herbicide tolerant crops always GM?
NO, herbicide tolerant crops are not always GM - but the majority planted today are
-can be simply selected by conventional methods (& therefor not regulated)
Glyphosate is..
an excellent herbicide
why is glyphosate a good herbicide?
- non-toxic (Debatable)
- Breaks down quickly in the soil
- Acts systemically against plants (sprayed on top will kill underneath as well, kills rhizomes)
- Acitive agent of ‘Round up’ - out of patent protection
- INITIALLY little or no resistance to weeds
problems with glyphosate as a herbicide:
-use in non-GM application is limited to pre-emergence (field clearance)
‘round up’???
- commercial product, glyphosate key ingredient
- spray & kills weed growing, not seed bank (including weeds)
traditional weed control:
- Ploughing
- -buries weeds and crop residues which then decompose
positives to ploughing:
- aerates the soil
- brings nutrients to the surface
negatives to ploughing:
- can increase soil erosion
- formation of a plough pan –> this affects root development
- reduces earthworms
- affects drainage
- labour intensive for farmers
low-till/ no-till agriculture:
- -> NO PLOUGHING
- no disturbance of soil through tillage
low-till/ no-till agriculture positives:
- reduces soil erosion
- reduces fuel costs
- improves soil structure
low-till/ no-till agriculture negatives:
- previous crops & weeds must be controlled
- can lead to increased herbicide usage
Glyphosate mode of action:
- glyphosate inhibits EPSPS, essential for the shikimic acid pathway
- we don’t use this pathway so it doesnt affect us (not toxic)
- All plants EPSPs are inhibited by Roundup
- The EPSP enzyme form the soil bacterium Agrobacterium sp. C4 is NOT inhibited
engineering resistance to herbicides:
- Find an EPSPs enzyme which is not inhibited by glyphosate
- engineer plants to contain this enzyme
- plants become resistant to the herbicide
are there weeds resistant to glyphosate
resistant weeds very unlikely but is happening
application of resistance to herbicides:
- fields can be sprayed post-emergence
- ‘environmentally friendly’ herbicides can be used
- soil tillage reduced minimising soil losses & run-off
potential problems with application of resistance to herbicides:
- transfer of genes to weed species
- crops can themselves become weeds
- increased selection pressure leads to weed resistance
- more herbicide may be applied
- improved weed control may affect wildlife
- same company owns seed & herbicides
Round up ready crops: Commercialised by ____ in:
- Monsanto in..
- cotton
- maize
- soybean
- -monsanto sell the seed and the herbicide (discourage competitors)
timeline for bringing Roundup ready soybean to market:
14 years from first transgenic plant to US commercialisation (source Monsanto)
how weeds evolve resistance:
- Herbicide application is a powerful selection pressure
1) Herbicide sprayed
2) Resistant plant survives & sets seed
3) Herbicide is used on weeds with more resistant plants in population
4) eventually majority of plants are resistant - –Repeatedly applying the same herbicide exerts the same selection pressure over & over
resistance to glyphosate is
RISING e.g. Argentina in GM soybean
problem: same company owns seed & herbicides
GURTS complication–> companies want to make seed that produce crops that don’t produce viable offspring, so farmers can’t use their crops for future crops, company has full control
how do we solve the problem of weed resistance?
1) produce GM plants resistant to a range of herbicides
2) Stack resistance genes
how do we solve the problem of weed resistance? produce GM plants resistant to a range of herbicides:
- use can be rotated
- weeds may be less likely to form resistance
GM plants resistant to herbicides have been ___
DEVELOPED
how do we solve the problem of weed resistance? STACK RESISTANCE GENES
- if the probability of finding a resistant mutant is 10^10
- then the probability of finding a mutant resistant resistant to 2 herbicides will be 10^20
- but the maths is wrong if you already have population of weed resistant to one herbicide
- multiple resistance has been found some weeds
whats the way forward to solving the problem of Herbicide-resistant weeds
- new herbicide resistant crops
- integrated weed management
whats the way forward to solving the problem of Herbicide-resistant weeds: NEW HERBICIDE RESISTANT CROPS
SHORT TERM: -intensification of selection pressure increase in herbicide use -sole use of herbicides LONG TERM: -increase in resistant weeds -increase in non target effects -fewer control options
whats the way forward to solving the problem of Herbicide-resistant weeds: INTEGRATED WEED MANAGEMENT
SHORT TERM: -reduction in selection pressure -decrease in herbicide use -use of multiple practices LONG TERM: -reduction in the severity of resistant weeds -environmental quality increases -preservation quality increases -preservation of knowledge
integrated Weed management methods of action:
- crop rotation
- cover crops
- competitive crop cultivars
- appropriate use of tillage
- more targeted herbicide application to reduce weed populations
- combining crop rotation & appropriate herbicide use has additive benefits
