Citrus canker is caused by which type of pathogen ?

Question

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Correct — option (1), Bacteria. Citrus canker is caused by the bacterium Xanthomonas citri subsp. citri (also referred to in older and regional literature as Xanthomonas axonopodis pv. citri), a rod-shaped, gram-negative bacterium. The pathogen enters citrus leaves, young stems and fruit through natural openings (stomata) or wounds, then multiplies in the intercellular spaces just beneath the surface, producing the disease's characteristic raised, corky, necrotic lesions, often ringed by a yellow (chlorotic) halo, on leaves, twigs and fruit. Severe infection causes defoliation, dieback, blemished and prematurely dropped fruit, and reduced yield, making citrus canker a serious quarantine disease for citrus-growing regions worldwide, actively managed through copper-based bactericide sprays, sanitation, wind-break planting to limit wind-driven spread, and destruction of infected material.

Why the other options are wrong — (b) Citrus trees are certainly susceptible to several fungal diseases — for example, citrus scab and various fungal fruit rots — but citrus canker specifically is not one of them; its causal organism is the bacterium Xanthomonas citri subsp. citri, not a fungal pathogen.  (c) Citrus is affected by well-known viral diseases too, most notably citrus tristeza virus, which causes a distinct set of symptoms (stem pitting, quick decline of trees on sour-orange rootstock). Citrus canker, however, is a bacterial disease, and its lesion pattern and disease cycle are characteristic of a bacterial, not a viral, pathogen.  (d) Plant-parasitic nematodes such as the citrus nematode (Tylenchulus semipenetrans) do attack citrus, but they infest roots and cause a distinct disease called citrus slow decline, affecting root function and overall tree vigour. They are not the cause of citrus canker's characteristic leaf, stem and fruit lesions, which are produced by bacterial infection.

Concept: Citrus canker is caused by the gram-negative, rod-shaped bacterium Xanthomonas citri subsp. citri, which infects citrus plants through stomata or wounds and colonises the intercellular spaces of leaf, stem and fruit tissue, producing raised, corky lesions typically surrounded by a yellow halo. The disease spreads locally via wind-driven rain, and over longer distances through movement of infected plant material, contaminated equipment, or, historically, citrus leaf-miner damage that creates additional wound entry points for the bacterium. Because it can devastate commercial citrus orchards and is easily spread, many countries treat citrus canker as a quarantine pest, with eradication and containment programmes (including destruction of infected and exposed trees) rather than relying on chemical control alone.

State PCS 2025 Q58 — Science & Technology PYQ with Answer

State PCS 2025 Q58 — Science & Technology PYQ with Answer