|Genetic Engineering of Biocontrol Agents
Occurrence of a number of interactions among the microorganisms provides a broad opportunity for genetic engineering of microbial biocontrol agents directed at plant pathogens or other microorganisms against weeds and pests. Several biocontrol agents have been successfully employed for such purposes in experimental or commercial agriculture (Panopoulos, 1986).
The effectiveness of biocontrol agents can be intensified by gene splicing, gene cloning and transformations (Papavizas, 1987). It is, however, obvious that bacterial pathogenicity on plant is determined by several genes. Certain genes encode enzymes involved in the biosynthesis of phytotoxins, growth hormones or enzyme capable of degrading plant cell wall or other constituents. Since these genes are positively needed for pathogenesis, their inactivation (e.g. through deletion-replacement technique) would destroy the organisms, their pathogenic potential or reduce virulence (Panopoulos, 1986).
Papavizas (1985) has discussed the future prospects of some wild type strains of fungal antagonists (viz., Aspergillus, Chaetomium, Dendrostibella, Gliocladium, Penicillium, Sporidesmium, Talaromyces, Tetraspenna and Trichoderma) for biological control of soil borne diseases.
In India, at National Institute of Immunology (Nil), New Delhi some genes of Baculoviruses have been engineered to make them 'suicide' (self destroying) after they have infected and killed the insect pests.
Genetic material of Baculoviruses is covered by a protein coat called polyhedrin. It is synthesized by a gene of the viruses. Scientists at Nil have made a suicide squads of Baculoviruses by removing the polyhedrin gene. After application, the genetically engineered Baculoviruses infect and kill the larvae, and millions of viruses, after completing their life cycle, are released into the environment. Soon after release, viruses die within a few hour as they lack polyhedrin, therefore, fail to survive. By making the viruses crippled before application, possible risk’ associated with virus release can be completely eliminated. Field trials of these have also been conducted at Tamil Nadu Agricultural University, Coimbatore.