Which of the following is a viral disease of plants?
- A.Red rot of sugarcane
- B.Bunchy top of banana
- C.Citrus canker
- D.Loose smut of wheat
Correct answer
Explanation
The correct answer is B, bunchy top of banana, a virus disease in which the plant is severely stunted and its leaves become short, narrow and crowded in a bunch at the top; it is carried by an aphid and by infected suckers used for planting, so control depends on clean planting material and on destroying the vector. Option A is wrong because red rot of sugarcane is fungal, caused by Colletotrichum falcatum. Option C is wrong because citrus canker is bacterial, caused by a species of Xanthomonas. Option D is wrong because loose smut of wheat is fungal, caused by Ustilago, and turns the ear into black spore dust. The way to recognise a viral disease in a list is by its symptom words: mosaic, mottling, leaf curl, bunchy top, yellow vein and stunting all point to a virus, while rot, blight, rust, smut and mildew point to a fungus.
Read the full article: Plant Diseases and Their Causes: Notes for Exams
Practice Questions
View allLate blight of potato is caused by which organism?
- A.A virus
- B.Phytophthora infestans
- C.Xanthomonas citri
- D.Meloidogyne incognita
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The epidemic of the 1840s destroyed the potato crop of Ireland and brought on the famine, and the study of that outbreak by Anton de Bary established plant pathology as a science.
Read the full explanation →Rust of wheat is caused by a fungus of which genus?
- A.Puccinia
- B.Ustilago
- C.Fusarium
- D.Claviceps
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The rusts of wheat, named black, brown and yellow after the colour of the pustules they raise on the stem and leaves, are caused by species of Puccinia, and resistance to them was one of the traits selected in the dwarf wheats of the Green Revolution.
Read the full explanation →Red rot, one of the most serious diseases of sugarcane, is caused by
- A.Colletotrichum falcatum
- B.Ralstonia solanacearum
- C.a phytoplasma
- D.a nematode
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The correct answer is A, Colletotrichum falcatum, a fungus that rots the internal tissue of the cane, turning it red with white patches and giving it a sour smell, and which spreads mainly through infected setts used for planting.
Read the full explanation →Citrus canker in plants is caused by
- A.a fungus
- B.a bacterium
- C.a virus
- D.a deficiency of boron
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Citrus canker is caused by a species of Xanthomonas, which enters through wounds, insect punctures and stomata and raises raised corky brown lesions, often with a yellow halo, on leaves, twigs and fruit; it spreads in splashing rain, on tools and on infected nursery plants.
Read the full explanation →Khaira disease of rice is caused by the deficiency of which nutrient?
- A.Zinc
- B.Boron
- C.Molybdenum
- D.Copper
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In khaira disease the leaves of young rice plants develop rusty brown spots that spread until the crop looks scorched, tillering is poor and growth is stunted; an application of zinc sulphate to the soil or as a foliar spray corrects it, which confirms that the cause is a deficiency…
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