Plant Diseases (B.Sc Agriculture)

Glassy winged leafhopper is characterised by leafhopper rain. While feeding, sharpshooters squirt small droplets of waste from the anus often called "leafhopper rain". These droplets are messy and, when the water evaporates, leave a residue that gives plants and fruits a whitewashed appearance.

Erwinia psidii is a Gram-negative bacterium and a phytopathogen of the common guava (Psidium guajava). It causes rot in branches, flowers and fruits.

Pseudomonas syringae is a rod-shaped, Gram-negative bacterium with polar flagella which causes holoblight of beans. This bacterium produces a toxin which causes systemic chlorosis.

Zebra chip is a recently diagnosed disease of potatoes associated with psyllid infestation and caused by species of the Gram-negative bacterium, Candidatus Liberibacter. The tubers frequently have discolouration which becomes clearer during frying of chips.

Grapevine is the common host for broad bean wilt virus, sowbane mosaic virus and petunia asteroid mosaic virus.

Ustiligo species causes smut of plants.

Magnaporthe grisea causes rice blast disease. Initial symptoms are white to gray-green lesions or spots with darker borders produced on all parts of the shoot, while older lesions are elliptical or spindle-shaped and whitish to gray with necrotic borders. Lesions may enlarge and coalesce to kill the entire leaf.

TMV causes mosaic disease in tobacco and tomatoes. Infection leads to internal browning of the fruit.

Aster yellow is caused by a bacterium-like organism called a phytoplasma. The symptoms include vein clearing until the entire leaf becomes chlorotic, stunting, deformation, virescence (greening of flowers), phyllody (development of leaf-like flower petals), reddening of foliage, reduced root system and sterility.

Brucella species causes infectious disease only in humans and animals. Thus, it is not a plant pathogen.

Erwinia tracheiphila causes wilt of cucurbitaceae. Wilt of carnation is caused by Burkholderia caryophylli.

Leafy gall disease is a bacterial disease. Rhodococcus fascians is a Gram-positive bacterial phytopathogen that causes leafy gall disease.

Stewart's wilt disease in maize is caused by Pantoea stewartii. Straw colored lesions appear on the leaf.

Cocksfoot mottle virus requires CMV's P protein for infection. The CMVP-protein interferes with RNAi pathways in Nicotiana benthamiana and Nicotiana tabacum.

Sorghum downy mildew is caused by Peronosclerospora sorghi. It is diagnosed by chlorosis of the leaves that is followed by white streaking of the leaves. The white streaked areas of leaves become necrotic over time that leads to a shredded leaf appearance. In the maturing plant, the reproductive structures do not form properly or do not form at all. This leads to a sterile plant.