Bt maize technologies: Insect pest control Anani Bruce Training course on identification and management of biotic stresses in maize 8-10 December 2015, Islamabad
1. What is Bt? Outline 2. How does Bt work in nature? 3. How have Bt crystal proteins been used in agriculture? Bt sprays 4. How have Bt crystal proteins been used in agriculture? Bt transgenes 5. How to create transgenic or Genetically Engineered crops
What is Bt? "Bt" stands for Bacillus thuringiensis a) Naturally occurring soil bacterium, discovered in 1901. b) Gram positive bacterium c) Produces Bt insect* crystal proteins (delta endotoxins) d) Stores the proteins in crystalline structures as a means of attacking insects that serve as a food source e) Biodegradable and not persistent in the environment
How does Bt work in nature?
How have Bt crystal proteins been used in agriculture 1. Bt Sprays a) Isolated and purified Bt crystal proteins b) Mixture of 3-7 different toxins Disadvantages a) Breakdown in sunlight b) Requires several applications c) Controls surface feeding insects only d) Does not control burrowed insects e) Expensive for high value crops only
How have Bt crystal proteins been used in agriculture? Bt delta-endotoxins a) Engineered into crops maize, tomato, potato, and cotton b) The genes are modified to ensure stable expression within the plant Advantages a) No need for sprays b) Can control burrowed insects c) Cheaper and easier to handle
Creating GE crops
Bt Maize The Success 1. Biotech maize (51.00 million hectares at 32%), 2. Insect resistant varieties occupied 23.9 million hectares or 15% of global area
GM in maize The cultivated area grown to genetically modified (GM) crops is in the increase and reached 148 million hectares in 2010 (James, 2010). The largest producer of GMO crops are the United States (67 million hectares), followed by Brazil and Argentina (25 and 23 million hectares, respectively), India, Canada, China, Paraguay, Pakistan, South Africa (2 9 million hectares). In European Union (EU) countries, insect-resistant maize has been cultivated since 1998, and genetically engineered potato with modified starch production has been grown since 2010 on a total of 245 hectares. Within the next 5 years, the number of transformation events for herbicide tolerance and insect resistance is predicted to increase, and new traits will be commercialised, such as optimised product composition for biofuel or industrial inputs, improved nutrient profiles and abiotic stress tolerance, e.g. against drought or salt.
GM in maize South Africa, is the only African country were white Bt maize is grown (James, 2007). Bt proteins have been used as a safe but expensive biopesticide for over 40 years. In contrast to Bt technologies, synthetic pesticides often kill non-target pests including their beneficial, in addition to the target pest. Bt crops are also particularly suitable for small-scale farmers since no equipment and pesticide knowledge are needed and these crops reduce exposure of farmers to insecticides, especially for those using hand sprayers (Heldt, 2006; Qaim and Janvry, 2005). The cultivation of Bt maize has reduced yield losses due to root worms and stem borers substantially without resorting to the more toxic organophosphate insecticides. It is estimated that Bt maize can substitute 40-50% of the insecticides currently in use (Heldt, 2006).
GM in maize Another benefit of Bt maize is the accumulation of less mycotoxins from opportunistic fungi that infect damaged kernels (Munkvold et al., 1999). Healthier cobs without insect damage are less likely to be infected by fungi, which produce mycotoxins that are harmful, and often lethal, to humans and livestock (Miller et al., 2006) Since 2005. indications of field resistance have been observed and documented. Fall armyworm, S. frugiperda, showed resistance to Cry1F in maize in Puerto Rico and was voluntarily discontinued (Matten et al., 2008) and resistance of the stem borer Busseola fusca to Bt transgenic maize was reported by Van Rensberg (2007), only 6 years after Bt maize was introduced in South Africa.
Major Insect Pests controlled by Bt Expression of Bt genes in tobacco and tomato provided the first example of genetically engineered plants for insect resistance (Barton et al., 1987; Vaeck et al., 1987). Subsequently, several Bt genes have been expressed in transgenic plants, including tobacco, potato, tomato, cotton, rice, etc In Africa, all events tested by CIMMYT in the laboratory produced high mortalities in the invasive stemborer Chilo partellus, but emergence holes noted in field plots raise concerns about the durability of those events (Mugo et al., 2008) For example in Kenya, differences between the yield on Bt trait and the isoline range from 0.46 to 1.89 t/ha (11 to 60%) for two seasons trails.
Challenges and opportunities for Bt Potential benefits, including reduced insecticide use and increased ability to invest in crop production and protection for growers in developing nations are considerable This is most important for resource-limited growers in places such as Africa, who currently rely on a diversity of tactics to manage insect pests. Of course, the worst scenario for the future would include the abandonment of IPM tactics followed by misuse and failure of GM maize due to evolution of pest resistance.
Challenges and opportunities for Bt potential impact on non-target species increase in toxin levels in the soil may affect soil microflora exchange of genetic material between the transgenic crop and related plant species leading to the development of so called Super weed and evolution of new and more virulent biotypes of the pests (Kumar, 2002).
Mortality (%) Leaf damage from Bt maize event MON810 on B. fusca and C. partellus 120 Bt Event 1 Bt Event 1 100 Non-Bt 1 Non-Bt 2 80 60 40 20 0 Busseola fusca Chilo partellus Eldana saccharina Sesamia calamistis Stem Borer Species
Insect Resistance Management Bt maize has revolutionized pest control in a number of countries and may allow growers to expand maize production into regions where high pest populations have made growing maize unprofitable (Hellmich and Hellmich, 2012). Compared to other IPM practices growing Bt maize, it is not knowledge intensive because the technology is in the seed. This should be attractive to growers in developing countries where poor infrastructure and inadequate extension services sometimes limit the use of conventional IPM (Shelton, 2007).
Conclusion 1. Bt is a naturally occurring bacteria discovered 100 years ago that produce crystal toxins it uses to kill specific insects for its food. 2. Purified Bt crystals proteins have been used as sprays for 50 years for protection of high value crops against insect pests. 3. Genetic engineering technology enabled transformation of maize cells with modified Bt genes for self defense against insect pests. 4. Bt maize has been safely used for 20 years in 29 countries to benefit many farmers and consumers globally.
Thank you for your interest!