thuringiensis. These are available in sachets as dried spores. Spores of this bacterium contain insecticidal cry protein. These spores
which are mixed with water and sprayed onto vulnerable plants such as Brassica and fruit trees, where these are eaten by the insect
larvae. In the gut of the larvae, the toxin is released and the larvae get killed. The bacterial disease will kill the caterpillars, but leave
other insects unharmed. Because of the development of methods of genetic engineering in the last decade or so, the scientists have
introduced B. thuringiensis toxin genes into plants. Such plants are resistant to attack by insect pests. Bt-cotton is one such example,
which is being cultivated in some states of our country.
Baculoviruses are pathogens that attack insect pests and other arthropods. The majority of baculoviruses used as biological control
agents belong to the genus Nucleopolyhedrovirus. These viruses are excellent candidates for species-specific, narrow spectrum
insecticidal applications. They have been shown to have no negative impacts on plants, mammals, birds, fish or even on non-target
insects. This is especially desirable when beneficial insects are being conserved to aid in an overall integrated pest management (IPM)
programme, or when an ecologically sensitive area is being treated.
some other biocontrol agents
• Phytophthora palmivora - Controls growth of milkweed vine
• Cercospora rodmanii - Controls growth of Eichhornia crassipes
• Praying Mantis - Successful in combating scale insect
• Beauveria bassiana - Successfully employed in controlling potato beetle
• Rodolia cardinalis - Controls cottony cushion scale (Icerya purchasi)
• Cyrtorhinus mundulus - Controls sugarcane leaf hopper.microbes as bioFertilisers
Chemical fertilisers are being used in increasing amounts in order to increase output in high yielding varieties of crop plants.
However, chemical fertilisers cause pollution of water bodies as well as ground water, besides getting stored in crop plants. Therefore,
environmentalists are pressing for switch over to organic farming. Organic farming is the raising of unpolluted crops through
the use of manures, biofertilisers and biocontrol agents that provide optimum nutrients to crop plants, keeping pests and
pathogens under control.
Biofertilisers are organisms which bring about nutrient enrichment of the soil by enhancing the availability of nutrients like nitrogen
and phosphorus to the crops. Some of the important biofertilisers recommended for the use in agriculture are discussed ahead.
microphos biofertilisers
They release phosphate from bound and insoluble states, e.g., Bacillus polymyxa, Pseudomonas striata, Aspergillus species.Free living nitrogen fixing bacteria
Free-living nitrogen fixing bacteria fix atmospheric nitrogen in the soil and make it available for the higher plants. The best example
is Azotobacter. Apart from Azotobacter, some other genera of free living soil enhabiting bacteria such as Clostridium, Bacillus
polymyxa, Beijerinckia, Klebsiella, Derxia and Rhodospirillum are also known to fix atmospheric nitrogen.
Inoculation of soil with these bacteria helps in increasing yield and saving of nitrogen fertilisers. For example, Azotobacter occurring
in fields of cotton, maize, jowar and rice, not only increase yield but also saves nitrogen fertiliser to the tune of 10–25 kg/ha. Its
inoculation is available under the trade name of azotobactrin.symbiotic nitrogen fixing bacteria
They form a mutually beneficial association with the plants. The most important of the symbiotic nitrogen fixing bacteria is Rhizobium.
The bacteria Rhizobium occurs freely in the soil but fails to fix nitrogen in the free state. It multiplies as soon as it gets to rhizosphere
of leguminous plants, enters into their roots and forms specialised structures called root nodules. The bacteria fix atmospheric
nitrogen only in the root nodules and that too when present in the bacteroid forms.
The genus Rhizobium includes many species and each species further includes many strains. It has been observed that a
specific strain of Rhizobium sp. gets symbiotically associated with specific species of leguminous plant, e.g., Rhizobium
leguminosarum (in pea), R. meliloti (in alfalfa), R. trifolii (in clover), R. phaseoli (in beans), R. lupini (in lupines) and
R. japonicum (in soybeans), etc. Therefore, it is important to apply specific strain of Rhizobium to a particular leguminous crop in
order to get maximum advantage.Frankia, a nitrogen fixing mycelial bacterium (actinomycete), is associated symbiotically with the
root nodules of several nonlegume plants like Casuarina, Alnus (alder) Myrica, Rubus, etc.