Q50. Plant disease pathogens may be carried from one plant to another by which media?
[RRB Group D — 09 February 2026, Shift 3]
(A) Soil alone
(B) Both soil and air
(C) Air alone
(D) Neither soil nor air
Answer: (B) Both soil and air
Explanation: Soil can carry persistent fungal structures and infected plant debris, while wind disperses many fungal spores. Water, seeds, tools and insect vectors are additional routes. Therefore, restricting transmission to either soil or air alone would be scientifically incorrect.
Q49. Rice blast should be classified primarily as which type of plant disease?
[CGPSC Preliminary Examination — 09 February 2025]
(A) Fungal
(B) Bacterial
(C) Nutritional
(D) Viral
Answer: (A) Fungal
Explanation: Rice blast is caused by the fungus Magnaporthe oryzae, also called Pyricularia oryzae in its asexual form. It forms characteristic lesions on rice leaves and can damage nodes and panicles. Humid conditions favour infection and spore dispersal.
Q48. Choose the correct matching sequence for:
A. Citrus canker; B. Sugarcane red rot; C. Potato blackheart; D. Sahu disease of wheat.
Factors: 1. Insect; 2. Oxygen deficiency; 3. Bacterium; 4. Fungus.
[UPPSC Combined State Examination (Prelims) — 12 June 2022]
(A) A-4, B-1, C-3, D-2
(B) A-1, B-3, C-4, D-2
(C) A-3, B-4, C-2, D-1
(D) A-1, B-2, C-3, D-4
Answer: (C) A-3, B-4, C-2, D-1
Explanation: The 2022 exam key pairs citrus canker with bacteria, red rot with fungus, potato blackheart with oxygen deficiency, and Sahu disease with insects. Caution: some secondary explanations inconsistently describe Sahu disease as fungal spot blotch; this particular matching key follows the exam.
Q47. Of these statements, which is correct?
I. Citrus canker is caused by a virus.
II. Wheat rust is caused by fungi.
[SSC CPO Tier I — 10 November 2022, Shift 1]
(A) Only statement II
(B) Neither statement
(C) Only statement I
(D) Both statements
Answer: (A) Only statement II
Explanation: Citrus canker is a bacterial infection, principally due to Xanthomonas citri, so statement I is false. Wheat rust diseases are caused by fungi of the genus Puccinia, making statement II true. Both affect economically important crops.
Q46. Which of the following names describes a disease symptom commonly seen in plants?
[SSC CGL 2021 Tier I — held 19 April 2022, Shift 1]
(A) Blight
(B) Mastitis
(C) Botulism
(D) Coccidiosis
Answer: (A) Blight
Explanation: Blight describes rapid browning and death of plant tissues and occurs in diseases of potato, tomato and several other crops. Mastitis concerns mammary tissue, botulism is a toxin-mediated illness and coccidiosis primarily affects animals.
Q45. Which class of microorganism is responsible for citrus canker?
[SSC GD — 25 November 2021, Shift 3]
(A) Virus
(B) Bacterium
(C) Fungus
(D) Protozoan
Answer: (B) Bacterium
Explanation: Citrus canker is caused by Xanthomonas citri subsp. citri. It produces raised corky lesions, often surrounded by yellow halos, on leaves and fruit. Rain splash, contaminated equipment and infected nursery material help spread the bacterium.
Q44. Which disease–pathogen matching set is correct: white rust of crucifers, Tikka of groundnut, green ear of pearl millet and red rot of sugarcane?
[RPSC Senior Teacher Grade II (Science) — 04 July 2019]
(A) Albugo candida; Colletotrichum falcatum; Cercospora arachidicola; Sclerospora graminicola
(B) Albugo candida; Cercospora arachidicola; Sclerospora graminicola; Colletotrichum falcatum
(C) Cercospora arachidicola; Albugo candida; Colletotrichum falcatum; Sclerospora graminicola
(D) Sclerospora graminicola; Colletotrichum falcatum; Albugo candida; Cercospora arachidicola
Answer: (B) Albugo candida; Cercospora arachidicola; Sclerospora graminicola; Colletotrichum falcatum
Explanation: White rust is caused by Albugo candida, Tikka leaf spot by Cercospora species, green ear by Sclerospora graminicola and red rot by Colletotrichum falcatum. Albugo and Sclerospora are oomycetes, traditionally grouped with fungi in older texts.
Q43. What does the scientific field of plant pathology study?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Only methods of spraying pesticides
(B) Only soil nutrition
(C) Only the growth of healthy plants
(D) Causes, development and management of plant diseases
Answer: (D) Causes, development and management of plant diseases
Explanation: Plant pathology examines the agents responsible for plant diseases, interactions with hosts, disease development and measures used to reduce losses. It includes fungi, bacteria, viruses, nematodes and physiological disorders, rather than being limited to pesticide application.
Q42. Which combination is necessary for the classical plant-disease triangle?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) A host and irrigation alone
(B) Susceptible host, virulent pathogen and favourable environment
(C) A pathogen and fertilizer alone
(D) A resistant host and dry conditions
Answer: (B) Susceptible host, virulent pathogen and favourable environment
Explanation: The disease triangle describes three interacting requirements: a susceptible plant, a capable pathogen and suitable environmental conditions. Even when a pathogen is present, disease may not develop if the host resists infection or the environment is unfavourable.
Q41. H. H. Flor developed the gene-for-gene concept while studying rust on which crop?
[RPSC Assistant Research Officer (Plant Pathology) — 12 February 2016, Morning]
(A) Wheat
(B) Barley
(C) Flax or linseed
(D) Pea
Answer: (C) Flax or linseed
Explanation: Flor studied flax rust, caused by Melampsora lini, and demonstrated corresponding resistance genes in the host and avirulence genes in the pathogen. This work became a foundation for understanding race-specific resistance in many crop–pathogen relationships.