Resistance Management Strategies in transgenic crops.pptx

Resistance Management Strategies in transgenic crops.pptx

1. DIVISION OF ENTOMOLOGY RAJASTHAN AGRICULTURAL RESEARCH INSTITUTE (SRI KARAN NARENDRA GRICULTURE UNIVERSITY, JOBNER) DURGAPURA – JAIPUR-302018 By : RAKESH KUMAR MEENA

2. Introduction to Bt toxins

3. Hofte and Whiteley (1989) B acillus thuringiensis ( bt ) genes S. No. Toxin Shape and Molecular waight Target pest 1. Cry I Bipyramidal , 130-140 KDa Lepidoptera 2. Cry II Cuboidal, 65-71 KDa Lepidoptera and Diptera 3. Cry III Rhomboidal, 73 KDa Coleoptera 4. Cry IV Polypeptides, 72-134 KDa Diptera 5. Cry V 80 KDa Coleoptera and Lepidoptera 6. Cry VI Nematodes

4. Principal pathotypes of Bt are -

5. Methods of producing transgenic crops 1. Indirect gene transfer method (Vector mediated)

6. 2. Direct gene transfer ( Vector less methods) Process of gene transfer through Microprojectile bombardment http ://www.agr.okstate.edu/ptf/chambergun.html

7. Mode of Action of Bt Toxins

8. Transgenic Plants Expressing Bt Toxins Bt toxins have been inserted into crop plants to provide protection against different groups of insect pests . Crop Gene Target pests Cotton cry1Ab/cry1Ac Bollworms Corn cry1Ab European corn borer Potato cry3a Colorado potato beetle Rice cry1Ab/cry1Ac Stem borers and leaf folders Tomato Cry1 Ac Fruit borer Brinjal cry1Ab/cry1B Shoot and fruit borer Canola cry1Ac Diamondback moth Soybean cry1Ac Soybean looper Corn cry1Ab/cry1A European corn borer Potato cry1Ab Tuber moth

9. Insect Resistance

10. Case or Field study The first study of a mechanism of resistance in a field-evolved Bt resistant strain was made by Ferre etal . (1991) using a colony of P. xylostella from the Philippines. In the resistant strain, a loss of specific binding to Cry lAb ( Ferre et aI ., 1991; Bravo et aI ., 1992) suggested that the resistance was due to a change in the Cry 1 Ab binding site. A field-collected strain of P. xylostella from Florida selected for resistance to HD-I was highly resistant to Cry l Aa , Cry l Ab , and Cry l Ac but not to Cry 1B, Cry 1C, and Cry 1D (Tang et al., 1996). Analysis of the binding characteristics of biotinylated toxins on brush border membrane vesicles showed a loss of binding to Cry 1 Ab in the resistant strain, whereas binding properties of Cry 1B and Cry 1 C remained unchanged (Tang et al., 1996).

11. Resistance of Insects against Bt Crops Pest Country Gene Crop Year (i) Year (r) Period Helicoverpazea USA Cry1Ac Cotton 1996 2002 6 Years Spodoptera frugiperda Puerto Rico Cry1F Maize 2003 2007 4 Years Busseolafusca South Africa Cry1Ab Maize 1998 2004 6 Years Pectinophora gossypiella India Cry1Ac Cotton 2002 2009 7 Years Dibarotica virgifera virgifera USA Cry3Bb1 Maize 2010 2013 3 Years

12. The practices aimed at reducing the potential for insect pests to become resistant to a pesticide. Bt IRM is of great importance because of the threat insect resistance poses to the future use of Bt plant-incorporated protectants .

13. 1. Planting refugia At least 5 rows or 20% of a farm’s corn acreage must be planted to non- Bt corn. R = resistant adult S = susceptible adult

14. Refuges of non- Bt host plants near Bt crops will promote survival of susceptible pests and Delay resistance substantially.

15. Seed mixtures strategies Seed mixture strategy involves random mixing of 20% non- Bt plants among Bt plants. Poor compliance of the Indian farmers to grow refuge crop in Bt cotton fields . Commercial packets of Bt seeds will also contain non-transgenic seeds premixed . However , the strategy of seed mixtures can become ineffective and unproductive if the frequency of resistant insect pests has already become unmanageable.

16. 2. Multigene strategy (Pyramided plants) Pyramiding A special case of gene stacking where at least two modes of action against the same target pest(s) are provided by two or more genes combined in a single genotype. To engineer crops that express at least two toxic compounds that act independently, so that resistance to one does not confer resistance to the other. This approach, called gene pyramiding, became a commercial reality in 2003 with the introduction of Bollgard II. A transgenic cotton plant that expresses the original Bt protein, Cry1Ac, and a second Bt protein, Cry2Ab . The two proteins act independently in that they bind to different receptors in the insect’s midgut .

17. Insects homozygous for one resistance gene are rare, insects homozygous for multiple resistance genes are extremely rare. A species cannot easily evolve resistance to both toxins because that would require two simultaneous, independent mutations in genes encoding the receptors. The low percentage of resistant individuals after many years of extensive exposure to Bt cotton, exemplify successful resistance management. Products like Bollgard II cotton contain two Bt proteins – Cry1Ac and Cry2Ab2 - for the control of lepidopteran pests. Both proteins are highly effective against the target pests and they differ in their mode of action require less refuge than single- Bt products

18. Pest Crop Country Toxins in pyramid Resistance detected Proactive and separate from one-toxin plants H. armigera Cotton Australia Cry1Ac, Cry2 AB None H.punctigera Cotton Australia Cry1Ac, Cry2AB None Remedial and concurrent with one-toxin plans D. virgifera Corn USA Cry3Bb, Cry34/35Ab Cry3Bb H.zea Cotton USA Cry1Ac, Cry2Ab Cry1Ac H.zea Cotton USA Cry1AC, Cry1F Cry1Ac P.gossypiella Cotton India Cry1Ac, Cry2Ab Cry1Ac S.frugiperda Corn USA Cry1F, Cry1A.105b, Cry2Ab Cry1F Table :- Bt toxin pyramids used proactively and separately from one-toxin plants or remedially and concurrent with one-toxin plants.

19. Very high levels of expression can be achieved by transformation of cry gene in chloroplasts (Kota et al 1999) The high dose strategy assumes that resistance to transgenic plants is recessive & is conferred by a single locus with two alleles , resulting in three insect genotypes susceptible homozygotes (SS), heterozygotes (RS), and resistant and susceptible adults Only rare RR individuals will survive a high dose produced by the transgenic crop and both SS and RS individuals will be susceptible to the toxin ( Matten et al 2004) Transformed tobacco chloroplasts with Cry 11a5 accumulated upto 3% of the total soluble protein gives protection against H. armigera (Reddy et al, 2002) 3. High dose strategy

20. Fig 5: Schematic representation of the “high dose-refuge” (HDR) strategy. The success of the HDR strategy depends on resistance being a rare and recessive trait and the genetically modified plants producing a dose of toxin sufficient to kill all homozygous susceptible individuals ( SSgreen ) and all heterozygous individuals with for both resistance and susceptibility alleles (RS-blue ).

21. Other resistance management tools 4. Scouting and applying insecticides as needed – No transgenic crop ( Bt crop) is a complete solution to all pest problems. Any trait is only effective against a subset of pest species , and the level of control of the target species is often imperfect. G rowers of transgenic crop varieties must continue to scout their fields for damaging insect populations and use insecticides when economic damage thresholds are reached . Application of insecticides to a target pest population will help control any portion of that population that may be developing resistance to the insect control proteins in the crop.

22. 5. Release of sterile insect

23. 6. Natural enemies -

24. CONCLUSION