NCERT Class 8 Science — Chapter 2: Microorganisms : friend and foe

mcqmedium

The plant disease "Citrus canker" is primarily transmitted through:

Official previous-year question

Verified 1 Aug 2026.

Options

AAir
BContaminated seeds
CInsect vectors
DIrrigation water

Did you get this right?

Solution

The correct option is

Air

Explanation

Citrus canker is a highly contagious plant disease caused by the bacterium Xanthomonas citri. It affects all types of citrus trees, including lime, oranges, and grapefruits, leading to significant economic losses in agriculture.

Detailed Analysis:

Mode of Transmission: According to standard biological classifications, the primary mode of transmission for Citrus canker is Air. The bacteria are spread from tree to tree by wind, rain splash, and overhead irrigation. Wind-driven rain is the most critical factor in the natural spread of the pathogen over short distances.
Mechanism: The bacteria enter the plant tissues through natural openings (stomata) or wounds caused by insects or mechanical damage. Once inside, they multiply and cause characteristic lesions.
Symptoms: The disease manifests as raised, corky, crater-like lesions on leaves, stems, and fruits. These lesions can cause leaf fall and premature fruit drop.

Key Takeaway:
Citrus canker is a bacterial disease primarily transmitted through air (wind and rain splash).

Your note

More from Chapter 2: Microorganisms : friend and foe

With reference to microorganisms, consider the following statements: 1. They are classified into four major groups: bacteria, fungi, protozoa, and algae. 2. They can survive only in moderate climates and die in ice-cold or hot spring environments. 3. Some microorganisms are unicellular, while others are multicellular. Which of the statements given above is/are correct?

medium

Which one of the following characteristics distinguishes viruses from other microorganisms?

easy

Consider the following statements regarding the habitat of microorganisms: 1. They are found in air, water, and soil but not inside the bodies of animals. 2. They can exist freely as well as grow on other organisms. 3. They are capable of surviving in deserts and marshy lands. Which of the statements given above is/are correct?

medium

Which one of the following human diseases is caused by a protozoan pathogen?

easy

Consider the following pairs of microorganisms and their classification: 1. Aspergillus : Algae 2. Paramecium : Protozoa 3. Penicillium : Fungi 4. Spirogyra : Bacteria How many of the above pairs are correctly matched?

hard

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The correct option is

Air

Explanation

Detailed Analysis:

Mode of Transmission: According to standard biological classifications, the primary mode of transmission for Citrus canker is Air. The bacteria are spread from tree to tree by wind, rain splash, and overhead irrigation. Wind-driven rain is the most critical factor in the natural spread of the pathogen over short distances.
Mechanism: The bacteria enter the plant tissues through natural openings (stomata) or wounds caused by insects or mechanical damage. Once inside, they multiply and cause characteristic lesions.
Symptoms: The disease manifests as raised, corky, crater-like lesions on leaves, stems, and fruits. These lesions can cause leaf fall and premature fruit drop.

Key Takeaway:
Citrus canker is a bacterial disease primarily transmitted through air (wind and rain splash).