Transcript Bio-Pesticides - WordPress.com

Oleh Irda Safni
Bio-Pesticides
1. Microbial pesticides consist of a
microorganism (e.g., a bacterium, fungus, virus
or protozoan) as the active ingredient.
• Microbial pesticides can control many different
kinds of pests, although each separate active
ingredient is relatively specific for its target
pest[s].
Bio-Pesticides
2. The most widely used microbial pesticides are
subspecies and strains of Bacillus thuringiensis, or
Bt. Some Bt's control moth larvae found on plants.
• Each strain of this bacterium produces a
different mix of proteins, and specifically kills one
or a few related species of insect larvae.
Bio-Pesticides
3. Plant-Incorporated-Protectants (PIPs) are
pesticidal substances that plants produce from
genetic material that has been added to the plant.
• For example, scientists can take the gene for the
Bt pesticidal protein, and introduce the gene into the
plant's own genetic material. Then the plant, instead
of the Bt bacterium, manufactures the substance
that destroys the pest
History of Bt
 In Japan, Ishiwata (1901) was the first to isolate Bacillus
sotto, agent of sudden-collapse disease
 In Thuringia, Germany, Berliner (1911) characterized Bt
 European farmers used Bt as pesticide
 First registered as a pesticide in the US in 1961
 1970s: commercialization
 Until 1977, only 13 Bt subspecies were described
 Classified into 40 different classes of crystal proteins (e.g.
cryIA, B, C; cryIIA, B, C; cryIIIA, B, C, etc.)
 Crickmore (1998) has proposed nomenclature endo-toxin
based on amino acid homology.
Host Range of Bt Toxin
1. Lepidopteran: butterflies, moth, etc.
2. Diptera: mosquito, black flies, house flies, etc.
3. Coleoptera: Leaf beetles
4. Arachinidae: Plant and animal mites
5. Nematodes: Plan and animal nematodes
6. Dactyoptera: cockroaches
Effect of cry proteins on several insects
1. CryI
: Lepidoptera-specific
2. CryII
: Lepidoptera & Diptera-specific
3. CryIII
: Coleoptera-specific
4. CryIV
: Diptera-specific
5. CryV
: Coleoptrea & Lepidoptera-specific
Properties of Toxin
Protoxin
: Up to 230 kD
Active toxin
: 65 kD
Extremely toxic at pico-mole concentrations
Susceptible insects killed by ingestion –
crystals alone
Limitation of Biopesticides
(spray formulation)
 Poor stability under field condition – frequent reapplication
required
 Bt endopores are inactivated rapidly when exposed to UV
radiation
 Half-life : a few hours – 10 days in most agricultural crops
 Vegetative cells and spores may persist at gradually
decreasing concentrations for weeks, months, or years as a
component of the natural microflora
 The soil borne and borer insects are difficult to control.
Bt spray application, limitations &
remedy through biotechnology
Limitations
Remedy through biotechnology
Insects feeding internally can’t be
controlled by spraying
Inserting Bt gene into bacteria which
colonize the plant vascular system
Foliar persistence is poor due to
photo-inactivation
Bt containing plasmids are introduced
into non-pathogenic leaf colonizers,
e.g. Pseudomonas fluorescences
Soil dwelling insects are difficult to
control
Plant root associated organims
(Pseudomonas) are cloned with Bt
toxin
Advantages of Bt gene cloning in Plants
 Growers will be freed from dependence on weather.
 Protection of plant parts which are difficult to reach by Bt
spraying, such as roots, shaded leaves, and borer insects
 No scouting of pest in the field is required.
 Cost of chemical insecticidal spray will be reduced leading
to less cost of cultivation.
 There is continuous expression of Bt toxin by the plant.
Transgenic Bt crops
o Tobacco (1987)
o Tomato (1988)
o Potato (1989)
o Maize (1992)
o Rice (1993)
o Sunflower (1998)
Bt cloned crops, its limitation and
remedy through biotechnology
Limitations
Remedy through biotechnology
Crops-having multi-pest complex are
not controlled by single cry protein
cloning
Inserting of multi-cry protein gene into
crops takes care of multi-pest crops
The cry protein expression is reduced
after around 60 days of crop maturity
Apart from cry protein, anti-feedant
protein genes are introduced in the
crop, e.g. trypsin inhibitors, juveniles
hormone esterase
Resistance may develop against
CryIA protein
Apart from CryIA protein gene, CryIIA
or other genes are also cloned in the
plant.
Who is going to have the last laugh?
Interaction of genetically engineered crops
and insects/pathogens is leading to the
development of alternative methods of
increasing crop productivity and
economically viable less damaging
systems
Fight is on between scientists and
nature for supremacy