Genetic Control of Pests and Plants

Genetic Control: Mechanisms of Genetic Manipulation of Pests and Host Plants

• Sterile Insect Technique (SIT): A widely used genetic control method for insects. Involves mass-rearing insects, sterilizing them (using irradiation or chemicals), and releasing large numbers of males to mate with wild females.
• SIT is environmentally friendly.

Example of Chemical Sterilant

• Tris-(1-aziridinyl) phosphine oxide is a chemical sterilant used in the SIT.
• Drawbacks: mutagenic and carcinogenic to humans and animals, posing environmental hazards. Use with caution.

Examples of Effective SIT Programs

• SIT programs eradicated screwworms in North and Central America.
• SIT programs also suppressed Mediterranean fruit fly populations in Florida and other locations.
• SIT and MAT (methyl eugenol as a lure, malathion as a poison) were used to suppress fruit fly populations in Guimaras, Iloilo (1996-1998).

Mechanisms of Host Plant Resistance to Insect Pests

• Host plant resistance: Involves the heritable property that enables plants to inhibit pest populations and recover from damage.
• Deployment of genes from wild relatives and novel genes in crops creates resistant plants.
• This is a weapon to minimize insect losses.

Mechanisms of Resistance in Plants

• Plant resistance to insects: Enables plants to avoid or suppress pest selection (inhibit oviposition and feeding). Reduces insect survival, development, and tolerates or recovers from significant damage.

Two Ways Plants Become Resistant to Insect Pest Attacks

• Ecological resistance: A false or pseudo resistance. The crop's environment plays the primary role.
• Genetic resistance: True resistance governed by resistance genes in the plant's genetic makeup.

Types of Ecological Resistance

• Phenological asynchrony: The crop's susceptible stage does not coincide with the pest's peak population.
• Induced resistance: Proper plant care, such as fertilization, makes the plant resistant to insect pests.

Mechanisms of Genetic Resistance to Insect Pests

• Genetic resistance: Under the primary influence of the plant's genetic factors and is true resistance.
• Painter (1951) classification: Classified insect resistance into non-preference, antibiosis, and tolerance.
• Antixenosis (non-preference): Pest is less likely to find or feed on a resistant plant.

Antibiosis

• Plant feeding harms the pest's health or fitness.
• This often involves chemicals in plant tissues that either kill, slow development, or reduce the reproduction of the pest species.
• Physiological effects of a plant's ingestion by an insect.

Tolerance

• The plant can continue to thrive despite pest attacks.

Host Plant Resistance to Diseases

• A host plant's ability to exclude or overcome a pathogen's effect.

• Resistant varieties are the best pest and disease control method.

• Plant varieties respond uniquely to specific pathogens.

International and National Plant Breeding Institutions

• Organizations develop resistant varieties (e.g., IRRI for rice, CIP for potatoes). Table details numerous institutions and crops.

Rice Varieties with Pest Resistance

• High-yielding rice varieties, such as NSIC Rc 216, Rc 160, Rc 300 (Tubigan).
• Newer breeds like Rc 222 (Tubigan 18s) were developed
• Rice Tungro disease resistant varieties (also known as "Matatag").

Mechanisms of Host Plant Defense Against Plant Pathogens

• Pre-formed Resistance: Passive defense mechanism.
• Induced resistance: Active resistance mechanism.
• Tolerance: Plant's ability to minimize the impact of a pathogen's infection on its health (despite infection).

Preformed Resistance Mechanisms

• Structural barriers: Thick cuticle, wax, partially closed stomates.
• Compounds: Pre-existing compounds (e.g., catechol and protocatechuic acid).
• Nutritional deficiencies: Lack of nutrients reduces pathogen growth.

Induced Resistance Mechanisms

• Pathogen-induced changes: Mechanical barriers, hypersensitive response (HR), phytoalexin production.
• Pathogen toxicity reduction: Detrimental toxins neutralization

Hypersensitive Reaction (HR)

• Rapid localized death of host cells around the pathogen, confining its spread.
• Lesions are small and localized.

Systemic Acquired Resistance (SAR)

• Initial pathogen infection can cause widespread resistance within a plant to other pathogens.
• It builds upon a HR (hypersensitive reaction).

Resistance Elicitors

• Substances produced by pathogens or their parts that stimulate plant defenses.
• These can induce plant resistance to other pathogens from the same or different class.

Synthetic Compounds as Resistance Elicitors

• Examples include: salicylic acid, aspirin, dichloroisonicotinic acid, chitosan.
• These compounds activate defense responses.
• Chitosan is effective against bacterial wilt in tomato, bacterial blight in rice, and bacterial heart rot in abaca.

Genetic Modification of Crops for Pest Resistance

• Time-consuming and resource-intensive process in plant breeding.
• Backcrossing is needed. Dominant genes require fewer generations, recessive genes require more.

Genetic Engineering of Crops

• Short-cut to introduce pest-resistance genes.
• Introduces specific DNA sequences (e.g., genes for insect resistance).
• Transferred genes often encode proteins with insecticidal activity.

Genetic Insertion Methods

• Methods include: gene guns, bacterial vectors (Agrobacterium), chemicals, or electroporation.
• A "promoter" gene from a virus is often included in genetic modifications to enable gene expression.

Genetic Engineering Examples

• Bt corn and cotton have genes from Bacillus thuringiensis for resistance to corn borers and cotton bollworms.
• PRSV-resistant Hawaiian papaya is a result of adding ringspot virus coat protein genes.

Advantages of Using Host Plant Resistance

• Cost-effective
• Specific to pests.
• Compatible with other control methods
• Long-lasting

Disadvantages of Using Host Plant Resistance

• Time consuming
• Limited pest range
• Potential for insect evolution
• Compatibility issues

This quiz explores the mechanisms of genetic manipulation used in pest control and the measures for enhancing host plant resistance. Topics include the Sterile Insect Technique (SIT), its applications, and examples of its effectiveness. Additionally, it addresses the environmental impacts of chemical sterilants used in these methods.