Question

Citrus canker is a disease caused by

• A. Bacteria
• B. Fungi
• C. Mites
• D. Deficiency of trace elements

Hint:

The genus Xanthomonas contains several important plant-pathogenic bacteria.
Associating Xanthomonas with citrus canker helps identify it as a bacterial disease.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Citrus canker is a highly contagious disease that affects citrus crops, including limes, lemons, oranges, and grapefruits.
Managing the disease requires identifying the causative pathogen.

Step 2: Detailed Explanation:
Citrus canker is caused by the Gram-negative, rod-shaped bacterium Xanthomonas citri (previously known as Xanthomonas axonopodis pv. citri).
The disease causes distinctive necrotic, raised lesions with oily or water-soaked borders on the leaves, twigs, and fruit of citrus trees.
As these lesions age, they become brown, corky, and crater-like, often surrounded by a yellow chlorotic halo.
These infections can cause premature leaf and fruit drop, twig dieback, and general decline in tree vigor.
The bacteria enter plant tissues through natural openings (stomata) or wounds caused by wind, hail, pruning tools, or pests.
The citrus leafminer (Phyllocnistis citrella) creates feeding tunnels that damage the leaf cuticle, providing easy entry points for the bacteria and worsening the severity of the disease.
Citrus canker is spread primarily by wind-driven rain and the movement of infected nursery stock or contaminated agricultural equipment.
Fungi, mites, and nutrient deficiencies can cause other plant health issues, but they do not cause citrus canker.
Therefore, the disease is bacterial in origin.

Step 3: Final Answer:
Citrus canker is a bacterial disease caused by the pathogen Xanthomonas citri.