General Science Quiz: Plant Diseases and Their Causes

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.

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.

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.

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.

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…

Where this micronutrient is short, the leaf blade of cauliflower fails to expand and the leaf is reduced to a narrow, whip-like strip along the midrib, which gives the disease its name; the curd is small or does not form at all.

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…

Bordeaux mixture is a suspension made by adding a solution of copper sulphate to one of lime, and it is the oldest fungicide still in regular use; it was devised in the Bordeaux region of France against downy mildew of the grapevine and is sprayed today on fruit trees, potatoes…

Phytoplasmas are bacteria without cell walls that live in the food-conducting tissue of the plant, and they are carried from plant to plant by sap-sucking leafhoppers, also called jassids; in little leaf of brinjal the leaves become very small and numerous, the plant bushes out and no fruit is set.

Root-knot is caused by microscopic soil roundworms of the genus Meloidogyne, which enter the young root, settle in it and make the surrounding tissue swell into knots or galls; the plant then cannot draw water properly and wilts in the afternoon heat even when the soil is moist.