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Different ways in which biotechnology can contribute to sustainable agriculture are: 1. Biofertilizers 2. Biopesticides 3. Disease and Insect Resistant Varieties 4. Single Cell Protein.
Way # 1. Biofertiliser:
There are certain microorganisms which have the capacity to enhance the availability of nutrients, e.g. nitrogen, phosphorous, etc. in soil for utilisation by crop. When such microorganisms are used in fields to reduce the amount of chemical fertilisers, they are known as biofertilisers. Plants are not capable of using nitrogen directly.
It can only be absorbed in the form of nitrates. There are certain organisms that directly utilise atmospheric nitrogen and are called as diazotrophs.
Certain important biofertilisers used in agriculture are:
i. Free Living Nitrogen Fixing Bacteria:
There are a number of free living bacteria which can convert free nitrogen into nitrogenous compounds. Clostridium plasturnum was the first bacteria in which this property was discovered. Some other free living bacteria are — Azotobacter, Chlorobium, Rhodospirillum and Micrococcus.
ii. Cynobacterial Biofertilizers:
Nostoc and Anabaena have the ability to fix soil nitrogen. Bacteria which fix soil nitrogen in rice fields are – Aulosira and Calathrix. Free living cyanobacteria are the largest contributors of biological nitrogen fixation.
Studies done in IARI, New Delhi have shown that cyanobacteria can fix 20- 30 kg of nitrogen per hectare of land. Using cyanobacteria as biofertiliser is more beneficial as it has low cost and is simple to use. Cyanobacteria can easily be cultivated in open tanks and also obtained from fields. Cyanobacteria can also be dried and stored for 2-3 years.
iii. Mycorrhizae:
Mycorrhiza is a highly evolved form of symbiosis between fungi and roots. There are two mycorrhizae – Ectomycorrhiza and Endomycorrhiza.
In ectomycorrhiza the fungal mycelia form dense sheath around roots and a net between root cells. The hyphae extend in the soil, absorb mineral from the soil and transport it to roots. It also converts insoluble organic compound into its soluble form. Ectomycorrhizae are found in oak, peach, eucalyptus, pines, etc. They can also absorb and store nitrogen, phosphorus, potassium and calcium.
In endomycorrhiza, the fungus produces loose mass of inter woven hyphae. Some hyphae enter the soil and others penetrate the root cortex. This is found in grasses and crop plants. They help in phosphate nutrition in plants.
iv. Nitrogen Fixing Fungi:
There are some fungi like Mactosporium, Cladosporium and Phoma, etc. which help in fixing free nitrogen.
v. Legume Rhizobium Symbiosis:
90% of leguminous plants can fix atmospheric nitrogen with the help of Rhizobium, Azorhizobium, etc. in root nodules. These are aerobic bacteria and can live saprophytically in soil till they infect the root hair cell.
vi. Azolla – Anabena Symbiosis:
Azolla is a fast growing small fern found in pools and pond surface. Cyanobacteria, Anabaena azollae lives in symbiotic association with leaf of Azolla. It can fix atmospheric nitrogen. This association is used as biofertiliser in rice fields where a 50% increase in yield has been recorded.
vii. Non-Legume-Frankia Symbiosis:
Frankia is an actinomycetes bacteria which shows symbiosis with non- leguminous angiospermic plants. Such angiosperms are called as actinorhizal plants and are perennial dicots, trees or woody shrubs. Examples of actinorhizal plants are – Casurina, Alnus, Dryas and Myrica. Frankia helps in fixing nitrogen.
viii. Azospirillum as Nitrogen Fixer:
Azospirillum lipoferum forms a loose association with roots of maize and Brazilian grass. Scientists have successfully isolated Azospirillum from roots of such plants and used it in combination with chemical fertilisers in the field. Application of Azospirillum has shown significant increase in yield.
ix. A transgenic crop plant can be created by adding nif gene. Such plants can fix atmospheric nitrogen without symbiotic association.
Way # 2. Biopesticides:
The traditional practice of controlling weeds and pests is the use of pesticides, herbicides and weedicides. By using these chemical compounds we are adding pollutants to the already polluted environment and increasing bio magnification. The best way to overcome this problem in to use biological agents. Biological agents that are used to control insects, weeds and pathogens in the fields are called bio pesticides. Bacteria, fungi, protozoa, viruses or even mites can be used as bio pesticides.
For different pests, different methods can be used. Certain insects can be used as a predator for the pests, e.g. lady bird and praying mantis are used to control Aphids. Certain bacteria like Bacillus thuringiensis produce an insecticidal protein thurioside. This can be used to kill a wide range of caterpillar pests.
The cry gene present in B. thuringiensis produces this protein which is also known as cry protein. B. thuingiensis was the first bacterium to be commercially used in the world and cry protein was the first protein to be produced on commercial scale in India.
This protein creates pores in the gut membrane which later cause death. Certain viruses like Bacula attack larvae of insect pests. Apple and some other plants suffer from crown gall disease. This can be checked by treating the seedlings and cuttings of non-pathogenic strains with Agrobacterium radiobacter.
There are certain chemical substances produced naturally in a few plants that have insecticidal properties. These chemicals have very little or no effect on humans. A few of them are Rotenone, Pyrethroids (from Chrysanthemum), Azoadiranchtin (from Azadiracta indica-neem) and alkaloids (nicotine).
Way # 3. Disease and Insect Resistant Varieties:
Plants can be infected by pathogens like virus, bacteria, fungi, nematodes, etc. With the help of genetic engineering such crop varieties can be produced which are resistant to the pathogens. The most common and successful approach is to insert the gene of virus coat protein into the plant. For this process, the gene encoding coat protein is isolated from the genome of the virus.
This can be inserted in the host cell where it expresses itself. When the gene expresses itself it creates resistance for the virus. This approach is used to generate virus resistant variety. Work is also in progress to create varieties which are resistant towards fungal and bacterial infections.
With the increase in such varieties there will be a reduction in the use of chemical pesticides which has a direct impact on the finance of farmers and also reduces pollution. Other than this, these varieties give good yield as the loss due to disease is reduced and so there is an increase in agricultural production,
Way # 4. Single Cell Protein:
Microbial proteins are dried cells of algae, bacteria, fungi and actinomycetes which can be used as food. Best example of this is yeast (Saccharomyces) used as leaving agent in bread industry. Lactobacillus and Sterptococcus are used in fermentation of milk and cheese in ancient times. In modern times microbial protein is called as Single Cell Protein (SCP).
The reason for this change is the single cell habit of the microorganisms used as food and feed. Protein produced on glucose or starch is called as mycoproteins. Other than glucose or starch, growth medium ranges from carbon dioxide to whey, saw dust and paddy straw. In certain cases SCP is processed, so that excess of nucleic acids can be removed. SCPs are low in fats and rich in high quality proteins both of which are desirable in human food.