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Questions and Answers
What is the primary purpose of using nitrogen fertilizers in soil?
Which of the following is NOT a type of therapeutic measure for diseased plants?
At what temperature is soil sterilized by steam in therapeutic measures?
What is the purpose of hot water treatment in therapeutic measures?
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What is the most effective temperature for refrigeration treatment to prevent post-harvest diseases?
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Which therapeutic measure uses physical agents such as temperature and radiations?
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What is a common method used to kill pathogens in post-harvest diseases of fruits and vegetables?
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Which of the following statements about hot air treatment is true?
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What is the primary function of fungicides in plant disease management?
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Which type of fungicide is applied to a host plant before pathogen exposure?
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Why are most fungicides considered effective only in areas where they are applied?
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Topical fungicides are primarily used for which type of fungal infection?
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What is the main difference between topical and systemic fungicides?
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Which type of fungicides is typically used after a plant has been infected with a pathogen?
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Which type of fungicide is used to treat infected seeds?
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Fungicides can function as disinfectants for what types of areas?
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What is the primary goal of treating plant diseases?
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Which of the following is NOT one of the broad categories of plant disease control measures?
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How do prophylactic measures primarily function in plant disease control?
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What is the purpose of plant quarantine?
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Which regulatory method is included in the exclusion measures for plant disease control?
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What does the term 'Eradication' refer to in the context of preventive measures?
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What is a primary function of systemic fungicides in plants?
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Which of the following best describes the role of plant quarantine stations?
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Which of the following systemic fungicides is used against post-harvest diseases?
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The legislation related to plant quarantine measures in India was first passed in which year?
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How is the Bordeaux mixture prepared?
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Which of the following systemic fungicides is primarily used to treat rust?
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What are Dithane R-24 primarily used for?
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Which of the following is NOT classified as an inorganic fungicide?
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Which of these systemic fungicides is categorized under Pyrimidines?
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Which systemic fungicide is derived from antibiotics?
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What is the main characteristic of a variety introduced through plant introduction?
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Which of the following best describes the selection method for breeding disease resistance?
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What is the primary goal of hybridisation in disease resistance breeding?
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Which of the following is NOT a method used to breed for disease resistance?
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What is a unique characteristic of plants developed through grafting?
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Which wheat variety is resistant to black and yellow rust?
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Which rice variety is recognized for its early maturing characteristic?
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What disease are varieties NP 15 and NO38 of arhar resistant to?
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Study Notes
Plant Disease Control
- Plant disease control focuses on protecting plant populations rather than individual plants, with exceptions for trees, ornamentals, and some virus-infected plants.
- Control measures aim to minimize losses caused by diseases.
- Selecting the appropriate control measure requires understanding the relationship between the pathogen and the host plant.
- Plant disease control is categorized into three main approaches: prophylactic (preventive), therapeutic (curative), and immunization.
Prophylactic (Preventive) Measures
- These measures are applied to prevent healthy plants from coming into contact with pathogens.
- Prophylactic measures are divided into three categories: exclusion, eradication, and protection.
Exclusion
- Aims to keep pathogens away from susceptible host plants.
- Achieved through regulatory methods such as quarantine and inspections.
Plant Quarantine
- Legal restrictions on the movement of diseased plant material or pathogens.
- Implemented in agriculturally advanced countries.
- The Destructive Insects and Pests Act in India (1914) imposes restrictions on shipments of diseased plant materials and pathogens.
- Quarantine stations at major sea and air ports check the entry of plant materials carrying pathogens.
- Imported plant materials and seeds require a certificate from the Ministry of Agriculture confirming disease-free status.
- Cultures of fungi and bacteria are only allowed into India with authorization from the authorized Mycologist.
Eradication
- Eliminating pathogens from a specific area to prevent disease outbreaks.
- Methods include destruction of infected plants, removal of infected plant parts, and soil sterilization.
Protection
- Measures that protect healthy plants from pathogen contact.
- Methods include using disease-resistant varieties, practicing crop rotation, and utilizing appropriate cultural practices.
Therapeutic (Curative) Measures
- Applied to treat diseased plants and plant parts.
- Aim to relieve symptoms and repair damage.
- Two types of therapeutic measures are physical therapy and chemical therapy.
Physical Therapy
- Involves treating plants, plant parts, and soil with physical agents like temperature and radiation.
Soil Sterilization by Heat
- Soil is sterilized by steam under pressure or through benches where steam is passed through the soil.
- Soil is heated to 82°C or higher for 30 minutes to kill soil-borne pathogens.
- Used in seed beds and greenhouses.
Hot Water Treatment
- Seed-borne smut diseases are eliminated by immersing infected seeds in hot water at 54°C for 10 minutes.
- Effective for roots and rhizomes infected with pathogens like Verticillium.
Hot Air Treatment
- Removes excess moisture from plant organs, protecting them from fungal and bacterial attacks.
- Treats viral-infected dormant plant materials at temperatures ranging from 35°C to 54°C.
- Hastens healing of wounds and protects them from weak pathogens.
Refrigeration (Low Temperature Treatment)
- Common method for preventing post-harvest diseases in fruits and vegetables.
- Storage plants are kept under low temperatures to inhibit pathogen activity and prevent secondary infections.
- Effective temperature is slightly above freezing point.
Treatment of Radiations
- Pathogens causing post-harvest diseases are killed by ultraviolet radiations, X-rays, gamma rays, alpha particles, and beta particles.
Chemical Therapy
- Uses chemical substances called pesticides to protect plants.
- Pesticides are classified based on the target organism: fungicides, bactericides, insecticides, nematicides, rotenticides, acaricides, herbicides.
Fungicides
- Chemical substances that kill fungal spores and mycelium.
- Used as eradicants or to control disease after infection.
- Most fungicides are not absorbed or translocated by plants, so they are only effective where applied.
- Some fungicides are absorbed and translocated, making them eradicants.
- Applied in different forms to various plant parts (foliage, seeds, tubers, bulbs, wounds, stored fruits and vegetables).
- Also used as disinfectants for soil and warehouses.
Types of Fungicides
- Protectants: Applied to the host plant before pathogen attack to kill the pathogen before it penetrates.
- Eradicants (Therapeutic): Applied after host infection to kill the pathogen after invasion.
Topical Fungicides
- Chemical substances applied to infected plant parts.
- Destroy pathogens in situ, confined to a specific spot or organ.
- Effective against powdery mildews, which are exoparasites on the host surface.
- Used for seeds infected with fungi and bacteria, killing the pathogen in situ.
- This type of chemotherapy is called topical chemotherapy.
Systemic Fungicides
- Provide immediate external protection to the host plant against fungal pathogens.
- Absorbed by roots or foliage leaves and translocated upward through xylem capillaries.
- Provide internal protection without harming the host.
- Act as both protective and eradicants.
- Chase pathogens throughout the host plant.
- Equally distributed within the plant, killing the pathogen through direct toxic action.
Common Systemic Fungicides
- Oxanthiins: Carboxin (Vitavax) for damping off diseases and smuts, Oxycarboxin (Plantvax) for rust.
- Benzimidazoles: Benomyl (Benlate) for powdery mildews, Cercospora leaf spots, smuts of wheat, apple scab, blast of rice, fruit rots, and Thiabendazole for post-harvest diseases caused by fungi imperfecti.
- Pyrimidines: Triarimol, ethirimel, and dimethirimol for powdery mildews.
- Dithane R-24 (Indar): Used against leaf rust of wheat.
- Antibiotics: Streptomycin, tetracyclines, and cycloheximide are used as systemic fungicides.
General Classification of Fungicides
- Fungicides are classified into two main groups: inorganic and organic fungicides.
Inorganic Fungicides
- Earliest fungicides used to control crop diseases.
- Main types include copper fungicides.
Copper Fungicides
- Bordeaux mixture: Most common fungicide, discovered in 1885.
- Prepared by mixing copper sulfate, lime (calcium hydroxide) and water.
- Effective against leaf spots, blights, anthracnose, downy mildews, and cankers.
- Fixed (insoluble) copper: Contains basic copper sulfate (Basicop), basic copper chloride, copper oxides, or cupric hydroxide.
- Used as dust or sprays and are less effective than Bordeaux mixture but effective against the same diseases.
Immunization Measures
- This approach involves developing disease resistance in plants.
- Achieved through breeding methods like plant introduction, selection, hybridization, mutation, polyploidy, budding, and scion grafting.
- These methods aim to introduce disease resistance genes into susceptible varieties, creating new resistant cultivars.
Plant Introduction
- Introducing a variety from its center of origin to a new environment with different disease pressures.
- Aims to introduce disease-resistant varieties to areas where the disease is prevalent.
Selection
- Selecting plants exhibiting disease resistance and growing them alongside susceptible plants.
- Plants are then infected with pathogens to test for resistance.
- Resistant plants are selected and tested across seasons and different locations to confirm consistent resistance.
Hybridization
- Cross-breeding a susceptible variety with a disease-resistant variety.
- F1 hybrids are tested for disease resistance.
- Resistant hybrids are selected for further investigation.
Grafting
- Used for asexually propagated plants where sexual reproduction is not possible.
- A graft of a disease-resistant plant is made onto a susceptible plant to create a new variety.
Examples of Resistant Varieties
- Wheat: Sonara 64, K 65, Lerma Rojo 64A, Sharbati Sonara, Kalyan Sona, Sonalika, Chhoti Lerma (S331), Safed Lerma, Hira, Lal Bahadur
- Rice: IR-8, IR-20, Jaya, Padma (dwarf), Hansa (early maturing), Pankaj, Kavery
- Arhar (Cajanus cajan): NP 15 and NO38 are resistant to wilt disease.
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Description
This quiz covers essential concepts of plant disease control, including preventive, therapeutic, and immunization measures. It delves into methods such as exclusion, eradication, and protection, offering a comprehensive understanding of how to maintain healthy plant populations. Test your knowledge on pathogen-host relationships and disease management strategies.
