Biotechnological Applications in Agriculture

• Food production can be increased by applying biotechnology by the following ways:

1. Agrochemical-based agriculture.

2. Organic agriculture; and

3. Genetically engineered crop-based agriculture.

• The Green Revolution succeeded in increasing food supply because of

1. use of improved crop varieties.

2. use of agrochemicals (fertilisers and pesticides).

3. use of better management practices.

• Agrochemicals are expensive for farmers in developing countries and also have harmful effects on environment. Therefore, genetically modified crops were developed.

• Genetically modified organisms (GMOs) are plants, bacteria, fungi and animals whose genes have been altered by manipulation.

• Genetic modification of crops has resulted in

1. increased tolerance against abiotic stresses (cold, drought, salt, heat).

2. reduced reliance on chemical pesticides (pest-resistant crops).

3. Helped to reduce post-harvest losses.

4. increased efficiency of minerals used by plants (this prevents early exhaustion of fertility of soil).

5. enhanced nutritional value of food, e.g., vitamin 'A' enriched rice (golden rice).

6. creation of tailor-made plants to supply alternative resources such as starches, fuels and pharmaceuticals to industries.

Bt cotton

• Some strains of Bacillus thuringiensis produce proteins that kill some insects like lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes).

• B. thuringiensis forms protein crystals which contain a toxic insecticidal protein.

• Bt toxins are initially inactive protoxins but after ingestion by the insect their inactive toxin becomes active due to the alkaline pH of the gut, which solublises the crystals.

• The activated toxin binds to the surface of midgut epithelial cells thus creating pores which causes cell swelling and lysis, further leading to death of the insects.

• Specific Bt toxin genes obtained from Bacillus thuringiensis are used in several crop plants like cotton.

• The toxin is coded by a gene called cry which is of various types. For example, proteins encoded by the genes cryIAc and cryIIAb control the cotton bollworms and that of cryIAb control corn borer.

• Bt tobacco was first cultured to kill hornworm (Manduca sexta).

Pest resistant plants

• A nematode Meloidegyne incognitia infects the roots of tobacco plants which reduces the production of tobacco.

• It can be prevented by using RNA interference (RNAi) process which is checked by silencing of specific mRNA due to a complementary dsRNA.

• dsRNA binds and prevents translation of the mRNA (silencing).

• By using Agrobacterium vectors, nematode-specific genes were introduced into the host plants which produce both sense and anti-sense RNA in the host cells.

• These two RNAs are complementary to each other and form a double-stranded RNA (dsRNA) that initiates RNAi and hence silence the specific mRNA of the nematode.

• The parasite cannot survive in the transgenic host, so protects the plants from pests.