bt hybrids and resistance management considerations...
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Bt Hybrids and Resistance Management Considerations –Experimental Evaluation of Multi-Gene
Insect Control Products
Illinois Corn Breeders’ SchoolMarch 1, 2010
Mike GrayDepartment of Crop SciencesUniversity of Illinois, Urbana-Champaign
We have a transgenic landscape in the corn and soybean production system.
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IllinoisUSA
USDA – Economic Research Service Estimates of Stacked Gene Varieties – IL and USA
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Average U.S. Corn Seed Costs – Projected for 2010 to be $82.50 per acre: NPK Fertilizer Advisory Service
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USDA – Economic Research Service Estimates of Genetically Engineered Corn Plantings – IL and USA
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Corn and Soybean Classic Springfield, IL January 11, 2010
Did you plant a Bt hybrid in 2009? Yes – 97.06% (n=132), No – 2.94% (n=4)
In 2009, did you plant a Bt hybrid for CRW or ECB control knowing that anticipated damage levels were low? Yes – 80.33% (n=98), No – 19.67% (n=24)
Did you have access to elite (high yield potential) non-Bt corn germplasm in 2009? Yes – 59.26% (n=80), No – 40.74% (n=55)
Would you be willing to use a seed blend (Bt and non-Bt) as a refuge? Yes – 79.14% (n=129), No – 20.86% (n=34)
If you answered “Yes,” would you be willing to use a seed blend that contains non-Bt seed in the 2 to 5% range? Yes – 88.41% (n=122), No – 11.59% (n = 16)
If you answered “Yes,” would you be willing to use a seed blend that contains non-Bt seed in the 6 to 10% range? Yes – 57.86% (n=81), No – 42.14% (n=59)
Transgenic Bt Corn Rootworm Products Agrisure RW – mCry3A Agrisure ECB/RW – Cry1Ab + mCry3A Herculex RW – Cry34Ab1/Cry35Ab1 Herculex XTRA – Cry1F + Cry34Ab1/Cry35Ab1 YieldGard RW – Cry3Bb1 YieldGard Plus – Cry1Ab + Cry3Bb1 YieldGard VT RW – Cry3Bb1 YieldGard VT Triple – Cry1Ab + Cry3Bb1 YieldGard VT Triple Pro – Cry3Bb1 + Cry1A.105 +
Cry2Ab2
SmartStax™ Hybrids Event MON88017 – Cry3Bb1 Event MON89034 – Cry1A.105 +
Cry2Ab2 Event DAS-59122-7 – Cry34/35Ab1 Event TC 1507 – Cry1F Glyphosate tolerance Glufosinate tolerance
Gene Pyramiding with Seed Mixtures – The Future of IRM Programs and Insect Management?
Nature Biotechnology 21, 1152 - 1154 (2003) doi:10.1038/nbt1003-1152
SmartStax (Monsanto Company) TrialUrbana, Illinois, 2008
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*Avg. node injury rating significantly greater than avg. node-injury ratings for all other treatments.
*
SmartStax (Monsanto Company) TrialUrbana, Illinois, 2008
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*Avg. node injury ratings with the same lower-case letter are not significantly different.
Gene Pyramiding: Will this Sustain Bt Durability?
Zhao et al. 2003. Transgenic plants expressing two Bacillus thuringiensis toxins delay insect resistance evolution. Nature Biotechnology. 21:12.
Greenhouse experiment with transgenic broccoli plants and diamondback moths with resistance genes to Cry1Ac and Cry1C proteins
After 24 generations of exposure to Bt broccoli, resistance to pyramided plants was delayed compared with plants expressing a single Cry protein
“Our experiments showed that allowing the concurrent release of cultivars with the two Bt genes in separate plants, each with one Bt gene, is not the best way to delay resistance. Even sequential release would result in control failure of at least one cultivar sooner than if pyramided varieties were used.”
Gene Pyramiding: Will this Sustain Bt Durability?
In 2002, pyramided cotton (Bollgard II®) that express Cry1Ac and Cry2Ab2 was approved in Australia and the United States. These “stacked” cotton plants have proven very
effective. The Cry proteins have different binding sites in the
insect midgut. Key to longterm durability of pyramided transgenic
plants is the absence of cross resistance.
Gene Pyramiding: Will this Sustain Bt Durability?
Most instances of resistance to Cry proteins is related to changes in receptor binding sites within the midgut of insects
Resistance also can potentially develop if rare individuals are able to alter the metabolism of Cry proteins
An integration of resistance management tactics (mosaic of refuges in the landscape) with pyramided plants is necessary
Implementation of IPM tactics along with Bt hybrids is recommended (use of scouting and economic thresholds to influence the temporal and spatial deployment of Bt hybrids)
Corn and soybean producers in the North Central Region of the United States are increasingly relying upon the use of two neonicotinoid insecticides applied as seed treatments: thiamethoxam (Cruiser ®) and clothianidin (Poncho®).
thiamethoxam clothianidin
All Bt (transgenic corn hybrids) have seed treated with a low rate (0.25 mg a.i./seed) of a neonicotinoid product (clothianidin or thiamethoxam). The refuge (non-Bt hybrid) may be planted to seed treated with the higher rate (1.25 mg a.i./seed) of the same neonicotinoid insecticide.
Percentage of Plants Infested in Farmers’ Fields Over a 10-Year Period
Perc
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Years Bigger and Petty (1965)
Corn Rootworm Control TrialPerry, Illinois, 2009
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Corn Rootworm Control TrialPerry, Illinois, 2009
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Corn Rootworm Control TrialUrbana, Illinois, 2009
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Are Bt hybrids for corn rootworm control bullet proof?
What does resistance look like?
YieldGard RW, August 2004
Significant rootworm injury to the roots of a YieldGard VT hybrid from the DeKalb site in 2008. (University of Illinois)
Significant rootworm injury to the roots of an HxXTRA hybrid from the DeKalb site in 2008. (University of Illinois)
Vaughn, T. et al. (2005). A method of controlling corn rootworm feeding using a Bacillus thuringiensis protein expressed in transgenic maize. Crop Sci. 45: 931-938.
Hybrid 1 – V4 (60.21 ppm); V9 (49.34 ppm) Hybrid 2 – V4 (61.98 ppm); V9 (40.5 ppm) Hybrid 3 – V4 (69.67 ppm); V9 (42.88 ppm) Hybrid 4 – V4 (75.17 ppm); V9 (42.33 ppm) Hybrid 5 – V4 (80.67 ppm); V9 (45.81 ppm)
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Planting Date (May 5, 2006) Urbana, IL 2006Av
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atin
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Evaluation Dates
Gray et al. 2007. J. Appl. Entomol. 131: 386-390
controlFailed to meet commercial standards
Field Evolved Resistance to Bt Crops
Resistance to Cry1Ac – some field populations of cotton bollworms (Helicoverpa zea) in Arkansas and Mississippi
Bt cotton producing the Cry1Ac protein did not meet the high-dose standard for H. zea.
“ … dominant inheritance of resistance to Cry1Ac appears to have hastened the evolution of resistance in H. zea.”
“ The hybrid progeny produced by matings between a laboratory-selected resistant strain and a susceptible strain of H. zea were resistant to Cry1Ac ..”
Tabashnik, et al. Nature Biotechnology, 26:2, February 2008
Field Evolved Resistance to Bt Corn Maize stalk borer (Busseola fusca) resistance
to the Cry1Ab protein in transgenic corn grown in South Africa
Fall armyworm (Spodoptera frugiperda) resistance to the Cry1F protein in transgenic corn produced in Puerto Rico
“Although published data are limited for these instances, failure to achieve the high-dose standard and to implement adequate refuges may have hastened resistance. To maximize knowledge gained from these and other cases, it is important for scientists in academia, industry, and government to make publicly available the relevant information on the efficacy of transgenic crops and refuge abundance.”
Tabashnik. 2008. Delaying insect resistance to transgenic crops. PNAS. 105: 49.
Meihls et al. 2008. Increased Survival of Western Corn Rootworm on Transgenic Corn within Three Generations of On-Plant Greenhouse Selection – PNAS, Vol. 105, No. 49.
Evolution of resistance to Cry3Bb1 reported within three generations of greenhouse selection – larval survival of 25%
After three generations, LC50 of constant-exposure colony was 22-fold greater than LC50 of control colony.
After six generations – percent survival on Bt corn compared with isoline was 11.7-fold greater in the field experiment for constant-exposure colony vs. control colony.
Summary Comments The use of neonicotinoids will continue to escalate in the corn
and soybean agroecosystem as the demand for transgenic crops increases.
At present no IRM plan is in place for the use of neonicotinoids in corn or soybeans – no plan is anticipated.
Resistance to this class of chemistry has been documented previously.
The prospects for resistance development to neonicotinoids and/or Bt, particularly by western corn rootworms, seems likely.
Producers will increasingly manage insect pests of corn using an “insurance” based approach (use of Bt hybrids) rather than rely on traditional (scouting and use of economic thresholds) IPM approaches.
Summary Comments Integration will increasingly come to mean use of
multiple pyramided genes in transgenic plants that express unique Cry proteins (or other novel proteins) with different binding sites within the insect gut.
Ultimately it is very likely that seed blends (transgenic and non-transgenic seed) will form the foundation of resistance management programs. This will ensure some baseline level of compliance.
Based upon current trends – seed costs will very likely continue to increase.