Bio pesticide - Bacillus thuringiensis PPT.pptx

Bio pesticide - Bacillus thuringiensis

1. Bio pesticide - Bacillus thuringiensis Classification and Characteristics Domain Bacteria Phylum Firmicutes Class Bacilli Order Bacillales Family Bacillaceae Genus Bacillus Species thuringiensis Structure: It is a rod-shaped bacterium (bacilli), about 2-5 µm long and 1.0 µm wide. It is a Gram + ve bacterium and it has a thick cell wall. This cell wall is made up of peptidoglycan. In between the cell wall and a plasma membrane a periplasmic space is present. This space is a small section that is responsible for protection and biosynthesis.

2. It has a circular-shaped chromosome. It has many plasmids. It forms spores. The lifecycle of  Bacillus thuringiensis  comprises a vegetative stage and sporulation phase. Under favourable conditions, the vegetative cell divides by binary fission and reproduces two daughter cells. Spores also germinate to produce a vegetative cell under favourable conditions. When sufficient nutrients are not available or under adverse environmental conditions, the bacterium sporulates and forms spores. Bacillus thuringiensis  produces endotoxin or delta endotoxin at the sporulation stage. It is a crystalline protein (cry proteins) and has insecticidal properties .

3. It also produces cytolytic or Cyt proteins. Cyt proteins are mosquitocidal and are moderately toxic to some mosquito larvae. These proteins are encoded by cry genes. They are produced as protoxins that need to be activated in order to have a toxic effect. Most Cry proteins are effective against lepidopteran insects. Some are also effective against dipteran (flies), coleopteran (beetles) and also against nematodes. In most strains of  Bacillus thuringiensis , cry genes are present in the plasmid.

4. Mechanism of Action of Bt -toxin Bacillus thuringiensis   is used to kill certain insects such as lepidopterans (tobacco budworm), coleopterans (beetles) and also some flies and mosquitoes (dipterans). The Bt -toxin crystal protein is present as inactive protoxins in the bacteria. The protoxin gets activated inside the midgut of insect larvae. The alkaline pH present in the midgut solubilises the crystal and makes it active. The active Bt -toxin binds to the glycoprotein or glycolipid receptors present on the epithelial cells of the midgut . It creates pores and forms a cation -selective channel in the cells and destroys the epithelial cells. As a result, the alkaline midgut juices flow into the haemolymph and increase the blood pH, leading to paralysis, inhibition of feeding and eventually to death.

5. If the receptors for Cry-proteins are absent, then the activated Cry-proteins are ineffective and are not toxic. e.g. in many lepidopterans and chewing insects. Sucking insects, spiders and mites are not susceptible to the cry protein, because the ingestion of the endotoxin crystal is necessary for the toxic effect. Under the highly acidic pH, as present in the stomach of humans and other vertebrates, the crystals of Cry proteins and Cyt proteins are solubilised but later degraded by proteolytic enzymes present in the gastric juices. They convert it to non-toxic peptides within minutes.

6. Biopesticide The first commercial bioinsecticide based on  Bacillus thuringiensis , “ Sporine ”, was produced in France. It was used primarily to control flour moths. Bacillus thuringiensis  is sold as dried spores in the market for biocontrol . Vulnerable plants are sprayed by the spore mixture. When the insect larva eats the spores, they reach the gut. In the gut, the Bt -toxin gets activated leading to the death of the larvae. It kills only the caterpillars of the target insects and other insects and invertebrates are unharmed. This bioinsecticide is used in fruit trees and flowering plants such as the genus Brassica .

7. The environment protection agency approved a CRY 3A Bt toxin that was produced from potato plants in 1985. It is the first human-modified pesticide that produces crops.  The European corn borer was killed by Bt Cry protein produced from genetically modified maize in 1996. The Bt genes were introduced in the corn there and it killed the corn rootworm larvae. By 2014  in India more than seven million farmers have adopted the Bt cotton by occupying the 2 million hectares.

8. Pest-resistant Plant The Bt -toxin gene is cloned and inserted into the plant genome by recombinant DNA technology. These genetically modified (GM) plants express the Bt -toxin genes and become pest-resistant. These GM plants do not require the application of chemical insecticides. Some of the examples of crops are Bt cotton, Bt corn, soybean, potato, etc. The Bt -toxin is coded by Cry genes. There are several Cry proteins coded by different Cry genes. The Bt -toxin is specific to insects. The gene is chosen according to the crop and the target pest. E.g. cryIAc and cryIIAb genes are effective against the cotton bollworms and cryIAb controls corn borer .

9. Nuclear Polyhedrosis Virus Nucleopolyhedrosis viruses (NPVs) belong to family baculoviruses (BV), which comprises 600 viruses, including two genera NPVs and Granuloviruses (GV ) NPVs are rod-shaped, 0.2 to 15 m size with double-stranded DNA Highly host specific . NPV can persist for years in a protected environment such as the soil, but is killed by exposure to ultraviolet light in sunlight, and high temperatures.

10. Enters through injection of plant material into the insect gut through mouth or cuticle.

11. The polyhedral capsid from which the virus gets its name extremely stable protein crystal that products the virus in the external environment. It dissolves in the alkaline midgut of mouths and butterflies to release the virus particle and infect the larvae. Hosts Current commercially-available formulations of NPV are registered for use against helicoverpa species. These products are not toxic to beneficial insects in the crop, but may impact larval parasitoids indirectly (if there is insufficient time to complete development in infected larvae).

12. Symptoms. Discoloration (Brown and Yellow) Stress Decomposition Lethargic After ingesting NPV, infected larvae will eat normally for a couple of days before reducing feeding substantially. Diseased larvae typically climb to the top of the plant to die. Shortly after death, the body becomes flaccid and its skin ruptures, releasing millions of infectious virus particles. When many larvae are living close together, they can infect each other and create an outbreak.

13. Life cycle and ecology NPV particles are called polyhedral inclusion bodies (PIBs), and must be eaten by the larvae for infection to occur . Once the PIB is ingested, the virus infects the gut cells, spreading to the blood within 24 hours, and then to almost all the tissue in the body. Even a single PIB is usually enough to kill a caterpillar. NPV can kill young larvae within 4 days of ingestion, and older larvae within 7 days, depending on dose and temperature. Cooler temperatures can prolong the larva's survival to more than 10 days.

14. Factors that influence effectiveness Temperature has a major impact : Daytime temperatures of 25–35°C are ideal for NPV activity. NPV activity is slower under cooler conditions (do not apply below 18°C). Larvae may stop feeding below 15°C, and take a while to recover. Delay applying NPV until temperatures have warmed to above 20°C following a cold night. Larvae death may take longer in cooler weather, but this will not influence overall damage levels. Infection relies on the larva ingesting the virus. Larvae in sheltered positions are more difficult to reach. Levels of 40–90% (average 60%) larval infection are possible on young cotton; however, in flowering cotton, larvae can shelter in squares and flowers. NPV will not control larvae sheltering in maize cobs, but will affect larvae on the silks.