Pathogenesis – Role of Enzymes, Toxins, Growth Regulators, and Polysaccharides
Plant Pathology MCQ E-Books Download1. What does the term “pathogenesis” primarily describe?
A. The treatment of diseases
B. The step-by-step development of a disease
C. The prevention of diseases
D. The immune response to diseases
Answer: B
2. Which is NOT a chemical weapon used by pathogens?
A. Enzymes
B. Toxins
C. Antibodies
D. Growth regulators
Answer: C
3. What is the primary function of cutinases?
A. Degrading pectin in the cell wall
B. Degrading cutin on the cuticle layer
C. Breaking down lignin in plant tissues
D. Inactivating toxins
Answer: B
4. Which enzyme group is responsible for breaking down pectin in plant cell walls?
A. Cellulases
B. Hemicellulases
C. Pectinases
D. Ligninases
Answer: C
5. Pectin methyl esterases (PME) primarily…
A. Degrade cellulose into sugars.
B. Remove methyl groups from pectin.
C. Break down lignin.
D. Facilitate photosynthesis.
Answer: B
6. The disease “bacterial soft rot” is associated with which enzyme?
A. Cutinase
B. Pectinase
C. Cellulase
D. Ligninase
Answer: B
7. Which plant pathogen produces cellulases?
A. Only fungi
B. Only bacteria
C. Only nematodes
D. Fungi, bacteria, and nematodes
Answer: D
8. What role do cellulolytic enzymes play in plant disease?
A. Form lignin in cell walls
B. Degrade cellulose and cause tissue collapse
C. Protect plants from nematodes
D. Deactivate toxins in pathogens
Answer: B
9. Hemicelluloses link which two compounds in the plant cell wall?
A. Lignin and cellulose
B. Cellulose and pectin
C. Glycoproteins and cellulose
D. Enzymes and lignin
Answer: B
10. Ligninases are primarily produced by…
A. Nematodes
B. Viruses
C. Basidiomycetes
D. Bacteria
Answer: C
11. The “wildfire disease of tobacco” is caused by which toxin?
A. Phaseolotoxin
B. Tentoxin
C. Tabtoxin
D. HC-Toxin
Answer: C
12. Tabtoxin inhibits which enzyme?
A. Glutamine synthetase
B. Ornithine carbamoyl-transferase
C. Cellulase
D. Polygalacturonase
Answer: A
13. Which toxin is responsible for “halo blight” in beans?
A. Tabtoxin
B. Phaseolotoxin
C. Tentoxin
D. HC-Toxin
Answer: B
14. Tentoxin targets which plant structure?
A. Mitochondria
B. Plasma membrane
C. Chloroplast coupling factor protein
D. Cell wall
Answer: C
15. Which of the following is a host-specific toxin?
A. Tabtoxin
B. Phaseolotoxin
C. HC-Toxin
D. Tentoxin
Answer: C
16. The Southern Corn Leaf Blight is caused by which pathogen?
A. Cochliobolus heterostrophus
B. Alternaria alternata
C. Gibberella fujikuroi
D. Plasmodiophora brassicae
Answer: A
17. T-toxin primarily affects which organelle?
A. Chloroplast
B. Nucleus
C. Mitochondria
D. Ribosome
Answer: C
18. Which growth regulator is primarily associated with cell elongation?
A. Gibberellins
B. Auxins
C. Cytokinins
D. Ethylene
Answer: B
19. “Foolish seedling disease” in rice is caused by…
A. Alternaria alternata
B. Agrobacterium tumefaciens
C. Gibberella fujikuroi
D. Rhizoctonia solani
Answer: C
20. The naturally occurring auxin in plants is…
A. Gibberellic acid
B. Cytokinin
C. Indole-3-acetic acid (IAA)
D. Ethylene
Answer: C
21. Clubroot of crucifers is caused by…
A. Gibberella fujikuroi
B. Plasmodiophora brassicae
C. Ustilago maydis
D. Agrobacterium tumefaciens
Answer: B
22. Crown gall disease is linked to which pathogen?
A. Agrobacterium tumefaciens
B. Plasmodiophora brassicae
C. Cochliobolus heterostrophus
D. Pseudomonas syringae
Answer: A
23. Which growth regulator can induce rosetting and leaf epinasty?
A. Gibberellins
B. Auxins
C. Cytokinins
D. Ethylene
Answer: D
24. What is the main function of cellulases in plant pathogenesis?
A. To degrade lignin in plant tissues
B. To degrade pectic substances in plant cell walls
C. To soften and disintegrate cell walls
D. To inhibit ATP synthesis in plant mitochondria
Answer: C. To soften and disintegrate cell walls
25. Which enzyme is responsible for degrading the cuticle layer of plants?
A. Cellulase
B. Cutinase
C. Ligninase
D. Hemicellulase
Answer: B. Cutinase
26. Pectinases are primarily involved in the degradation of which plant component?
A. Lignin
B. Hemicellulose
C. Middle lamella
D. Cutin
Answer: C. Middle lamella
27. Which organism is known to produce ligninases for lignin degradation?
A. Basidiomycetes (white-rot fungi)
B. Rhizoctonia solani
C. Pseudomonas syringae
D. Alternaria alternata
Answer: A. Basidiomycetes (white-rot fungi)
28. The “wildfire disease of tobacco” is caused by which toxin?
A. Tentoxin
B. Tabtoxin
C. Phaseolotoxin
D. Hc-toxin
Answer: B. Tabtoxin
29. What is the mode of action of tabtoxin?
A. Inhibition of ATP synthesis
B. Binding to chloroplast proteins
C. Inhibition of glutamine synthetase
D. Degradation of pectin
Answer: C. Inhibition of glutamine synthetase
30. Which plant disease is associated with phaseolotoxin?
A. Bacterial soft rot
B. Halo blight
C. Clubroot of crucifers
D. Southern bacterial wilt
Answer: B. Halo blight
31. Tentoxin primarily targets which cellular process?
A. Water transport in xylem
B. Cell wall degradation
C. Light-dependent phosphorylation of ADP
D. Degradation of hemicellulose
Answer: C. Light-dependent phosphorylation of ADP
32. Which plant disease is caused by the host-specific toxin T-toxin?
A. Southern Corn Leaf Blight
B. Halo blight
C. Oat leaf blight
D. Tobacco wildfire disease
Answer: A. Southern Corn Leaf Blight
33. T-toxin specifically targets which cellular organelle?
A. Chloroplast
B. Ribosome
C. Mitochondria
D. Nucleus
Answer: C. Mitochondria
34. Which plant hormone is most associated with cell elongation?
A. Ethylene
B. Auxin
C. Gibberellin
D. Cytokinin
Answer: B. Auxin
35. The fungal pathogen Ustilago maydis is responsible for which disease?
A. Crown gall
B. Clubroot of crucifers
C. Corn smut
D. Halo blight
Answer: C. Corn smut
36. The “foolish seedling disease” of rice is caused by: A. Pseudomonas syringae
B. Agrobacterium tumefaciens
C. Gibberella fujikuroi
D. Sclerotinia sclerotiorum
Answer: C. Gibberella fujikuroi
37. Gibberellins were first discovered in which fungal pathogen?
A. Alternaria alternata
B. Gibberella fujikuroi
C. Cochliobolus victoriae
D. Pseudomonas syringae
Answer: B. Gibberella fujikuroi
38. Ethylene production in infected plant tissues is primarily due to: A. Pathogen-induced synthesis in the host
B. Direct secretion by bacteria
C. Direct secretion by fungi
D. Activation of pectinases
Answer: A. Pathogen-induced synthesis in the host
39. Which of the following is NOT a symptom associated with altered auxin levels?
A. Stunting
B. Root branching
C. Leaf epinasty
D. Chlorosis
Answer: D. Chlorosis
40. Host-specific toxins like Hc-toxin and T-toxin are primarily distinguished by their ability to: A. Act on multiple plant species
B. Specifically target susceptible host plants
C. Degrade plant cell walls
D. Inhibit ethylene production
Answer: B. Specifically target susceptible host plants