1. Which of the following statements best defines “biotrophs” in plant pathology?
a) Organisms that can only grow and reproduce in dead plant tissue.
b) Organisms that require living host tissue for their nutrition.
c) Organisms that can survive independently of plant hosts.
d) Organisms that infect both plant and animal hosts.
Answer: b) Organisms that require living host tissue for their nutrition.
Explanation: Biotrophs are plant pathogens that rely on living host tissue to obtain nutrients, often without killing the host immediately, in contrast to necrotrophs that kill host cells.
2. Which of the following is the primary characteristic of a necrotrophic pathogen?
a) It only affects plants in specific environmental conditions.
b) It relies on living plant tissue for survival and reproduction.
c) It kills plant cells and tissues to obtain nutrients.
d) It produces systemic symptoms across the entire plant.
Answer: c) It kills plant cells and tissues to obtain nutrients.
Explanation: Necrotrophs kill plant cells and tissues to feed on them, often leading to visible tissue death and decay. They thrive in areas where host tissue is dying or damaged.
3. Which of the following is NOT a method of pathogen entry into plants?
a) Natural openings like stomata and lenticels
b) Mechanical injury to the plant surface
c) Through the vascular system without physical wounds
d) Through the cuticle layer only during rainstorms
Answer: d) Through the cuticle layer only during rainstorms
Explanation: While the cuticle can be a barrier for pathogens, it is not the primary route for pathogen entry. Pathogens typically enter through natural openings, mechanical injury, or direct penetration of tissues.
4. What is the primary function of the appressorium in plant pathogenic fungi?
a) To produce reproductive spores for further infections.
b) To anchor the fungus to the plant tissue.
c) To penetrate the plant cell wall.
d) To spread the infection across the plant’s vascular system.
Answer: c) To penetrate the plant cell wall.
Explanation: The appressorium is a specialized structure formed by plant pathogenic fungi that helps the pathogen to penetrate the host plant’s cell wall by generating high turgor pressure.
5. Which of the following best describes the term “host specificity” in plant pathology?
a) The ability of a pathogen to infect a wide range of plant species.
b) The tendency of a pathogen to infect only one species or a group of closely related species.
c) The ability of a pathogen to survive in the environment without a host.
d) The resistance of a plant species to most pathogens.
Answer: b) The tendency of a pathogen to infect only one species or a group of closely related species.
Explanation: Host specificity refers to a pathogen’s preference or ability to infect specific plant species or closely related groups, often determined by compatibility between the pathogen’s virulence factors and the host plant’s immune responses.
6. Which of the following is the primary cause of the disease “Powdery mildew” on plants?
a) A virus
b) A fungus
c) A bacterium
d) A nematode
Answer: b) A fungus
Explanation: Powdery mildew is caused by a group of fungi in the order Erysiphales. These fungi form white, powdery growths on the surface of leaves and other green plant tissues.
7. What is the significance of the “disease triangle” in plant pathology?
a) It is used to calculate the economic impact of plant diseases.
b) It emphasizes the interaction between the host, pathogen, and environment in the development of disease.
c) It predicts the spread of a plant disease across large geographic regions.
d) It helps identify the genetic resistance of plants to specific pathogens.
Answer: b) It emphasizes the interaction between the host, pathogen, and environment in the development of disease.
Explanation: The disease triangle model in plant pathology highlights the importance of three factors: the presence of a susceptible host, a virulent pathogen, and conducive environmental conditions for disease development.
8. Which of the following is a common method used to control fungal plant pathogens in agriculture?
a) Applying antibiotics to infected crops
b) Using crop rotation with non-host plants
c) Increasing the soil pH
d) Installing humidity control systems in greenhouses
Answer: b) Using crop rotation with non-host plants
Explanation: Crop rotation with non-host plants helps break the life cycle of soil-borne fungal pathogens, reducing their prevalence and severity in subsequent crop seasons.
9. Which of the following is the most common mode of transmission for bacterial pathogens in plants?
a) Airborne spores
b) Root-to-root contact
c) Through insect vectors and mechanical injury
d) Via soil water movement only
Answer: c) Through insect vectors and mechanical injury
Explanation: Bacterial plant pathogens are often transmitted by insect vectors (such as aphids or beetles) or mechanical injury (such as pruning or harvesting), allowing them to spread rapidly between plants.
10. What is the function of “hypersensitive response” (HR) in plants during pathogen infection?
a) It enhances the growth of plant tissues to limit pathogen access.
b) It induces rapid cell death at the site of infection to restrict pathogen spread.
c) It produces systemic acquired resistance throughout the plant.
d) It increases the susceptibility of the plant to future infections.
Answer: b) It induces rapid cell death at the site of infection to restrict pathogen spread.
Explanation: The hypersensitive response (HR) is a plant’s defense mechanism that leads to localized cell death at the infection site, limiting the pathogen’s ability to spread further in the plant.
11. Which of the following plant diseases is caused by a virus transmitted by aphids?
a) Late blight
b) Tobacco mosaic virus (TMV)
c) Cucumber mosaic virus (CMV)
d) Wheat rust
Answer: c) Cucumber mosaic virus (CMV)
Explanation: Cucumber mosaic virus (CMV) is primarily transmitted by aphid vectors, affecting a wide range of plant species.
12. Which of the following is a key characteristic of an effective plant disease resistance gene (R gene)?
a) It produces antimicrobial compounds that kill the pathogen.
b) It triggers a plant immune response upon recognition of a specific pathogen.
c) It limits the reproduction of the pathogen inside the host plant.
d) It prevents pathogens from entering plant tissues.
Answer: b) It triggers a plant immune response upon recognition of a specific pathogen.
Explanation: R genes in plants code for proteins that recognize specific pathogen-associated molecular patterns (PAMPs) and trigger an immune response, which helps the plant resist infection.
13. What is the role of “mycorrhizal fungi” in plant pathology?
a) They cause diseases by infecting plant roots.
b) They enhance plant growth by facilitating nutrient uptake and act as a defense mechanism.
c) They are the primary pathogens of root rot.
d) They help in the spread of viral diseases.
Answer: b) They enhance plant growth by facilitating nutrient uptake and act as a defense mechanism.
Explanation: Mycorrhizal fungi form symbiotic relationships with plant roots, improving nutrient uptake (especially phosphorus) and offering some protection against root pathogens.
14. Which of the following is the best method to manage bacterial wilt disease caused by Ralstonia solanacearum?
a) Use of resistant crop varieties
b) Applying chemical pesticides directly to the soil
c) Increasing irrigation in affected fields
d) Burning infected plants and rotating crops
Answer: d) Burning infected plants and rotating crops
Explanation: Burning infected plants and rotating crops helps reduce the population of Ralstonia solanacearum in the soil, which is crucial for managing bacterial wilt.
15. Which of the following methods is most commonly used for diagnosing plant diseases in the field?
a) Electrophoresis of plant tissues
b) Molecular identification using PCR techniques
c) Visual inspection of symptoms and signs
d) Genetic modification of the plant
Answer: c) Visual inspection of symptoms and signs
Explanation: In the field, diagnosing plant diseases typically begins with visual inspection of symptoms (such as lesions, discoloration, or wilting), which can help identify the potential pathogen or disease.