APPLICATION OF BIOTECHNOLOGY IN AGRICULTURE- Bt CROPS
Biotechnology has also revolutionized research activities in the area of agiculture.
To increase food production there are three options;
1. use of chemical fertihzers and pesticides,
2. use of bio-pesticides and biofertilizers (organic farming) and
3. use of genetically engineered crop plants i.e. transgenic plants or Bt crops.
Transgenic plants carrying desirable traits like disease resistance, insect resistance, and herbicide resistance are produced.
Plants with better photosynthetic efficiency, nitrogen fixing ability, improved storage proteins, and higher vitamin content can be produced.
Most of the current commercial applications of modem biotechnology in agiculture aim at reducing the dependence of farmers on agrochemicals.
Therefore insect resistant crops/ Bt crops are produced
Bacillus thuingiensis (Bt)
It is a soil bacteium that produces a protein with insecticidal qualities.
Traditionally, an insecticidal spray, produced from these bacteria is used.
- Bt toxin proteins occur as inactive protoxins.
- When an insect ingests it, due to the alkaline pH of the gut, it gets converted into the active form.
- The activated toxin cause swelling in the gut and death of the insect.
There are several Bt toxins and each one is speciic to certain target insect.
Crop plants have now been engineered using rDNA technology, to contain and express the gene for Bt toxin.
The gene is called 'cry' gene. It produces inactive protoxins when an insect ingests the transgenic crop it dies.
Bt cotton is now commercially available in India to control the disease affecting the cotton bolls.
Bt toxin gene has been cloned and introduced in many plants to provide resistance to insects without the need of insecticides.
Other examples are Bt corn, rice, tomato, potato and soyabean.
Agrobacterium tumefaciens
It is is a soil bacterium which causes crown gall tumours in dicotyledonous plants.
A gall producing gene (T DNA) occurs in a large plasmid called tumour inducing plasmid or Ti plasmid.
Due to the ability of the bacterium to insert Ti plasmids into nuclear genome of the infected plant, gene transfer in higher plants through Ti-plasmids can be achieved.
Tumour producing gene becomes the marker gene.
Therefore A. tumefaciens is most widely used for gene transfer.
Cry gene from B.thuringiensis or Nif gene (N2 fixing gene) from Rhizobium is cloned inside A. tumefaciens and then transferred into other plant.
Many Bt crops, transgenic plants or genetically modified plants (GM plants) are produced using A. tumefaciens.
For example ;
Flavr savr tomato
developed by introducing an antisense gene that retards ripening.
It produces less cell wall degrading enzyme polygalactouranase.
Therefore these tomatoes have longer shelf life.
Flavour is saved, which is an additional advantage.
Golden rice
genetically engineered rice with greater pro-vitamin A (beta carotene) content.
