environmental risks from transgenic crops
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Environmental Risks from Transgenic Crops
Jonathan GresselDepartment of Plant Sciences
Rehovot, Israel
Pontifical Academy of Sciences
May 18, 2009
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y
A newbook
(Johns Hopkins Univ. Press - 2008)
deals with further domesticating under-domesticated crops that lack genetic diversityAnalyze and proposes where to get the genes
Developing world has many such crops
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Transgenics allowrapid
domestication
Bring in genes
from whereever
Activate /suppress
specific geneswhenever
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HIVWitches
Problems in Africa
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These arebeautiful plants
Photo: Lytton Musselman
HIV=HighlyInvasiveVegetation
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that were nevercontrolled until they
emerged from thesoil, which is toolate.
Striga hermonthica(witchweed) onsorghum in Africa
Photo: Lytton Musselman
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Photo: Lytton Musselman
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Human population displacements facilitatedisease epidemics
- war- labor migration- land abandonment
Causes:- labor migration- land abandonment
HIV=Highly Invasive Vegetation
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Parasitic weedsgerminate afterstimulation by croproots, and growtowards the croproots, attach, and
suck nutrients
Strigaalso poisons
the crop.
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Sucks
Cant remove by hoeing!
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Cannot remove with a hoe
A
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A t eory was ormu ate -The herbicide should move un-metabolized from the leaf, through thestem into the parasite, underground
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14Orobanche spp similarly attack other crops
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It took some convincing to get industry toprovide the genetic
material for testing
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+chlorsulfuron + glyphosate
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How could this work for Striga?
farmers cant afford herbicidesto spray over whole fields
farmers cantafford sprayers
Approach:Treat crop seeds with herbicides instead of fieldNeed target-site resistant crops having a very
large margin of resistance.
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Joel Ransom FredKanampiu
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IR maize (homozygous)
ALS try552 leu
Pioneer AmCy (BASF)
A mutant obtained through biotech
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Photo: Dennis Friesen
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Technology for witchweed commercializedfor maize through local seed companies
But not sorghum - although at least threegroups now trying to get same mutant in
genetically - there is a good reason whytransgenic better than mutant selection
Better technologies coming on line:e.g.Dan Kiambi (Nairobi) RNAi in crop for Strigaspecific genes
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Jane Rissler:
Herbicide resistant crops are..a capitalist conspiracy..(and later).. a male chauvinist conspiracy
Florence Wambugo:A womens place is in the lab engineeringherbicide resistant crops so other women
should not have to weed by hand
E i t l Ri k f T i C
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Environmental Risks from Transgenic Crops
Jonathan GresselDepartment of Plant Sciences
Rehovot, Israel
Pontifical Academy of Sciences
May 18, 2009
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European Corn Borer Lep pests worldwide
16M ha infested in U.S. >60M infested ha
1-3 borer generations per year Yield losses often >30%
Mean 6% yield loss; up to 30% (Ostrinia, Spodoptera)
Non-Bt Corn
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What is environmental impact
Statistician compared to what?
Most studies do not compare to current agprocedures
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Some African farmers put insecticide in whorl- medicine dropper
- pinch of granules
Bt gene being put in maize - but not sorghum
torage o p osp orus n p ants
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torage o p osp orus n p ants
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these P groups bind Fe and Zn
Major crops produce ca 50 M tons phytate/yr
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Major crops produce ca. 50 M tons phytate/yr-binding 9 M tons phosphorus - not available tomono-gastric animals
Must add inorganic P to feeds of mono-gastricmammals, poultry and fish (not ruminates) -excrete the phytate, which releases pollutant
levels of PPeople zinc and iron deficientThree approaches:
1. add thermostable phytase to feed(transgenically over-produced by microbes)2. Lower phytate production by breeding ortransgenics3. Transform cro s with h tase enes
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Oilseed rape is favored for temperate climes
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Oilseed rape is favored for temperate climes
Is it nice to the environment?
Worldwide, oilseed rape emits ca. 9000 Tons
Before the ban Europe consumed 18,000T ofmethyl bromide
Is natural MeBr ok and synthetic bad?Is it ok to double the area - for biofuel?*Gan, J., et al. (1998) Production of methyl bromide by terrestrialhigher plants. Geophysical Research Letters25, 3595-3598
Brassica has a bifunctional methyl
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Brassicahas a bifunctional methyl-transferase
methylates halides to methyl halides (MeBr)methylates bisulfides to methanethiol
(goes to H2SO 4 to acid rain)
TDNA disruptive insertion in relatedArabidopsis HOL (harmless to ozone layer)gene reduced MeBr >99%
To meet intent of methyl bromide ban andreduce acid rain, must cultivate onlytransgenic oilseed rape with this genesuppressed; non-transgenic should be banned
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30% oil seeds get US$140/ton (optimistic)
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30% oil - seeds get US$140/ton (optimistic)- fruits hand harvested- fruits dried in the shade
- seeds removed by handIs Jatropha a gimmick to keep the poor poor?
Processingreminiscent ofbackyard steel
mills in Chinaduring theculturalrevolution
Info not in sites promoting Jatropha curcas
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Info not in sites promoting Jatropha curcascommon plant names: Black vomit nut, Purge nut, etc.common oil names: hell oil, oleum infernale, etc.
Toxins: Curcin (a toxalbumin) - similar to ricinPhorbol esters - diterpenoids Alkaloidsskin tumor promoters
No antidote knownSee: http://www.inchem.org/documents/pims/plant/jcurc.htmAlso: A case of Jatropha poisoning resemblingorganophosphate intoxication Clin. Tox. 44 337,2006Could one release a transgenic crop with suchcomponents? What to do with toxicbyproducts?
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Websites claim curcin is heat degradableQuoted citation says degradable by prolongedautoclaving
What to do with toxic byproducts?
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What to do with toxic byproducts?
Websites suggest - Use residue as manure
no environmental impact studies
Could one release a transgenic crop with such
components? Jatrofraud! ?
Remember - with soybeans there is morevalue from meal than oil.Where are the economics of discardingcastropha meal?
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Are countries cultivating guinea pigs?
Where is precautionary approach?
If you want Castropha as an oil crop -
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If you want Castropha as an oil crop -engineer or breed:- dwarfing (increase harvest index)
- single stalk (high IAA?)- Antishattering - fruits dry on stems
-machine harvesting and threshing
- RNAi curcin genes- RNAi terpene synthase to rid of phorbols-better yield, oil content / quality
The engineered crop might then beenvironmentally/human safe to grow
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The press warnsabout
The implications are that natural ecosystems
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The implications are that natural ecosystemsare endangered
Peter Raven dispelled this
The newspapers tell us:
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The newspapers tell us:
Horizontal gene flow often implied
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Horizontal gene flow is rare in eukaryotes
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Good source ofinformation
Does notdifferentiate
between wild andweedy
Usually the problemis weedy
Two perceived problems from
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Two perceived problems from
transgenic crops
1. Can the crop become a volunteerweed?
2. Can the crop introgress transgenetrait into related wild species?
These problems are not unique to
transgenic crops; they are general toall crops.
The question usually asked is:
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The question usually asked is:Can transgenic trait introgress (cross intoand become established) in related wild
species?If the answer is yes Introgression Feversets in.
If the answer is yes,the question so what?should be asked
So what? means:
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So what? means:How likely is introgression? when? where?What are the consequences?
Can the related hybrid or its offspring becomeweeds?
Does gene have selective advantage?
Will there be over-riding benefits tillintrogression occurs?
Some crops have severe weed problems from
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Some crops have severe weed problems fromrelated weeds:
RiceSorghumWheat (limited areas - diagonal only)Oilseed rape
SunflowersSugarbeetCarrots
No problems in corn, soybean or potatoes
How did these weed problems evolve?
Ancient man has domesticated many crops
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Ancient man has domesticated many crops
Stages of Domestication
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Cropprogenitor
Wildspeciesnear home
Stages of Domestication
millennia
Gathering Planting/selection more selection
Crop
Wildspecies
Bettercrop
Modern breeding Transgene technology
centuryBetter yetcrop2 decades
millennia
Wildspecies Weeds
At the same time:
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CropWild SpeciesDomestication
Crop
centuries/millennia(recessive traits)
Volunteerweed
Shattering De-domestication
annuallyFeral weed
cumulative(dominant traits)shatteringsecondary dormancyheight, branching, etc.
Ferality is thus an evolutionary problem
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Move from transplanting to direct seeding
Transplanted field
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Feral
p f- ca. 10% yield loss predicted
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Taller than crop and matures earlier- shatters
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Found in one Malaysian paddy
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y p y
cultivated
Another case: Sorghum bicolor
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Another case: Sorghum bicolor
Feral/weedy type(shattercane)
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Few selective herbicides can control
feral/weedy sorghum in sorghum or maize
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Sorghum crosses with a native wild species
X =
Sorghum halepense
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g p
johnsongrass
Stupidlyspread byman
Evolved resistance toALS, ACCase and
glyphosate
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We must learn about
the feral weedyenemy, and make surethat the right things
get done to keep itunder our control!
For more information
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For more information- see the book
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A non-transgenic herbicide resistant rice
Gave excellent control of weedy ricefor 2-3 yearsResistant gene introgressed into weedy rice
technology lost
Must prevent gene flow- by not making transgenic rice/sorghum
At places where
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At places where
stupidities flourish
Wisdom is considered aweed
Can wisdom be used to delay / precludeintrogression?
Two types of transgenic strategies proposed:
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yp g g p p
- Containment
- keeping the gene in the crop
- Mitigation
- preventing establishment and spread ofescaped transgenes
How do they work?
Containment Strategies
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Terminator or similar GURT(genetic
use restriction technology)
Chemically induced promotersInsert gene(s) of choice into plastome
Plastids maternally inherited-no pollen transmissionRepressible seed-lethal system.Schernthaner et al PNAS100, 6855-9, 2003Single generation transformationUse of attenuated viruses
to transientlytransform crops
g
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Mitigator technology
A primary (e.g. Bt, herbicide resistance)transgene is coupled in tandem with
mitigator genes that are positive or
neutral to a crop but deleterious to
offspring
Need genes that are carriers of incompetencel k
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in volunteers and offspring, ok in crop
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Two types of mitigators
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- Eco/morphological
Unfitness of hybrids/offspring is due toecological or morphological traits
- Eco/biochemicalUnfitness due to super-susceptibility torotational herbicides
Both can be transgenically stacked with eachother
Lets think about some TM genes by looking atth diff b t i d d i
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the differences between rice and red rice
Genes for dwarfing, anti-shattering orno secondary dormancy would turn a
weed into a non-competitive entity
Eco-morphological differences
TM genes that would be neutral or useful for theb t d l t i t th l t d d
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crop but deleterious to the related weedDwarfing has been transgenically achieved with:
antisensing many genes for GA biosynthesis introducing truncated GA receptor gene (GAI)- antisensing brassinosteroid biosynthesis genes introducing antisensed phytochrome genes
- prevents shading response in a crop(no perception of end of day FR) PHYPapophytochromes (PHYA, PHYB, PHYE)
PHYB- Robson et al. Nature Biotech14: 99, 1992
PHYD Aukerman et al. Plant Cell9: 1317, 1997PHYE Devlin et al. Plant Cell10: 1479, 1998
Antiweediness Transgenic Mitigation Traits
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Antiweediness Transgenic Mitigation Traits(Anti) Seed Shattering Prevents weed replenishing seedbank Prevents crop from being volunteer Prevents crop lossGenes:
Determinacy (uniform ripening/harvest) Shatterproof (no dehiscence layer)
A ti di ss T s i Miti ti T its
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Antiweediness Transgenic Mitigation Traits(Lack) of secondary dormancy
Genes: Arabidopsis abscissic acid insensitive
Steber et al. Genetics 149: 509, 1998
enhance gibberellin biosynthesis Abolish light requirement (phytochrome) (Anti) wall thickening
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Will studying a model of Beethoven teachh h d f?
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ywhy he was stone deaf?
Any evidence Transgenic Mitigation works?
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Hani al-Ahmad exPhD student
ype
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Generated
transgenicTobacco
120
2 5
WT Alone TM Alone Measure
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0
40
80
120
60 80 100 120 140
12.5
5
cm
60 80 100 120 140
1/ 2.5
5cm
Mixed SegregantsWT TM
0
40
80
cm
12.5cm
2.5
1
Time (d)
height ofWT andTM grownseparately
and mixed1:1
Al-Ahmad, Galili & Gressel Mol. Ecol 13:697-710, 2004
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Similar results with dwarf TM oilseed rape
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Al-Ahmad et al. Plant Biotech J. 4:23-33, 2006
Oilseed rape (B. napus)
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Non-transgenic
Alone
Mixed (1:1)
TM
5-cm spacing
yield/plant
Transgenic mitigated oilseed rape has highproductivity and low competitive fitness
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productivity and low competitive fitness
Biotype Productivity
grown alone(mg/plant)
Reproductive
fitness incompetitionwith B. napus
B. napusNT 320B. napusTM 503 0.20B. rapa 119
Al-Ahmad and Gressel, Plant Biotech J 2006).-increased yield when grown by itself- unfit in competition with wild type- unfit when crossed into B. rapa
T d BThus
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-increased yield when grown by itself- unfit in competition with wild type
- unfit when crossed into B. rapaWorks in the field Neal Stewarts group
Transgenic mitigated B. napus:
Similar mitigation strategies to preventestablishment of weedy rice/sorghum -many useful genes already cloned for
dwarfing and anti-shattering Eco-biochemical gene flow mitigation
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PloS One 3(3):e1818.Doi:10.1371/journal.pone.0001818
(Despite title not containment)
1. Use cv A and glyphosate2. Use cv B and glufosinate
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g fvolunteers and hybrids are super-sensitive toglufosinate - killed
3. Use cv A and glyphosatevolunteers and hybrids super-sensitive toglyphosate - dead
4. Use cv B and glufosinatevolunteers and hybrids super-sensitive toglufosinate - deceased
5. Use cv A and glyphosate
volunteers and hybrids killed by glyphosate6. Use bentazon + selective graminicidebentazon kills super-sensitive volunteers /hybrids
Such a rotation would:kill weedy rice 5 of 6 seasons
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- kill weedy rice 5 of 6 seasons- prevent establishment of hybrids with
weedy rice - all seasons- kill herbicide resistant Echinochloa5
of 6 seasons (or 6 of 6)
- extremely delay evolution of all weedresistances to all herbicides used
Will work even better if eco-biochemicalmitigation coupled with morphologicalmitigation
In summary - earn rom:- Non-transgenic herbicide resistance rapidly
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Non transgenic herbicide resistance rapidlyappears in weedy rice -Cibus Genetics
- Transgenic herbicide resistance could allowselective control of weedy rice / otherweeds - but genes could flow
- Two types of strategy to deal with gene flow:1. Containment
probably always leaky - escapes canpropagate
2. Mitigationintrogressed progeny always less fit -stay at low frequency unless selection
pressure - Transgene flow can be mitigated
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- Evolution of herbicide resistance delayed
Best strategy:Stack containment with mitigation
get unfit escapes
There are severe regulatory problems to beovercome - multigene constructs
Industry must collaborate to compete withweeds
Otherwise herbicides lost!
Biotechnology can prevent / mitigate transgeneintrogression regulators should ensure it is done
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g gwhere needed - and prevent unacceptable levels ofgene flow
Only with hand me down genes
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The developing world needs new genes
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We must decide:
Use biotech to helporSit and do nothing
The world needs solutions
- must consider transgenics to supply them e n t e west nee more mo esty
We should beware of cultural imperialism
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p
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