Plant Diseases: Bacterial, Viral, Fungal and Deficiency Diseases

Diseases are not only caused in humans, organisms such as bacteria, viruses and fungi cause various diseases in plants too. Deficiency or shortage of mineral elements also results in plant diseases. This topic - "Plant Diseases and their causes" covers different plant diseases caused by bacteria, viruses, fungi, and deficiency of mineral elements.

• Bacterial plant diseases or plant diseases caused by bacteria
• Viral plant diseases or plant diseases caused by viruses
• Fungal plant diseases or plant diseases caused by fungi
• Plant diseases caused by deficiency of mineral elements

1. Bacterial plant diseases

• Crown gall disease: Bacterium Agrobacterium tumifaciens causes crown gall disease in plants. This bacterium has been now reclassified as Rhizobium radiobacter. It contains tumor-inducing (Ti) plasmid and transfer DNA (T-DNA). It is used in genetic engineering.
• Wilt of Potato caused by bacterium Pseudomonas solonacearum: This disease is also called ring disease because of the presence of brown ring on the xylem.

Fig.1: Wilt of Potato

• Black arm of Cotton and bacterial blight of cotton caused by Xanthomonas bacteria.
• Bacterial leaf blight of rice caused by bacterium Xanthomonas oryzae.
• Citrus canker caused by bacterium Xanthomonas citri: This disease originated in China.

Fig.2: Citrus Canker

• Tundu disease of wheat: Bacterium Corinobacterium tritici and nematode Anguina tritici are causative organisms of this disease.

2. Viral plant diseases

• Tobacco Mosaic Disease (TMD): TMD is caused by Tobacco Mosaic Virus (TMV). It is characterized by the shrinking, stunting and mottled appearance of leaves beside the destruction of chlorophyll.

Fig.3: Tobacco mosaic disease

• Bunchy top of banana is caused by banana virus.
• Necrosis in potatoes disease and Potato Mosaic disease are caused by Potato Virus-X (PVX).
• Potato leaf roll disease is caused by potato leaf roll virus.

3. Fungal plant diseases

• Early blight: It is caused by Alternaria solani. In this disease, brown necrotic spots develop on leaves.  The spots are angular in shape.  
• Late blight of potato: Phytophthora infestans causes this disease. It is a water mold.
• Rust of wheat: It is caused by Puccinia graminis tritici. In this disease, red brown rust is visible on stems and leaves. This disease is controlled through the use of sulphur gineb, dithane, M-45, etc.

Fig.4: Rust of Wheat

• Loose smut of wheat: It is caused by Ustilago tritici. This disease spreads through seeds and affects inflorescence. It can be controlled through triazole fungicides. 
• Powdery mildew of wheat: Blumeria graminis .sp. tritici causes this disease. Powdery conidia are visible on leaves. It is controlled through fungicides and silicon solution.
• Red rot of sugar cane: Glomerella tucumanensis (Colletotrichum falcatum) causes this disease. This disease is characterized by drying of leaves and change in their color.
• Ergot of bajra is caused by Claviceps fusiformis.

4. Plant diseases caused by deficiency of mineral elements

• Deficiency of copper: Lemon’s dieback disease and little leaf disease.
• Deficiency of zinc: Khaira disease of paddy.
• Deficiency of manganese: Marsh disease of pea and phagla blight disease of sugarcane.
• Deficiency of sulfur: Tea yellow disease.
• Deficiency of boron: Fruit cracking in tomato and rough skin of guava and citrus.
• Deficiency of potassium: Marginal leaf drying in rice.
• Deficiency of calcium: Blossom end rot in tomato.

Fig.5: Blossom end rot in tomato

Summary

Bacterial plant diseases or plant diseases caused by bacteria: Crown gall disease (Agrobacterium tumifaciens), Wilt of Potato (Pseudomonas solonacearum), Black arm of Cotton and bacterial blight of cotton (Xanthomonas), Bacterial leaf blight of rice (Xanthomonas oryzae), Citrus canker (Xanthomonas citri), Tundu disease of wheat (Corinobacterium tritici)

Viral plant diseases or plant diseases caused by viruses: Tobacco Mosaic Disease (Tobacco Mosaic Virus, TMV), Bunchy top of banana (banana virus), Necrosis in potatoes and Potato Mosaic disease (Potato Virus-X, PVX)

Fungal plant diseases or plant diseases caused by fungi: Early blight (Alternaria solani), Late blight of potato (Phytophthora infestans), Rust of wheat (Puccinia graminis tritici), Loose smut of wheat (Ustilago tritici), Powdery mildew of wheat (Blumeria graminis .sp. tritici), Red rot of sugar cane (Glomerella tucumanensis), Ergot of bajra (Claviceps fusiformis)

Plant diseases caused by deficiency of mineral elements: Copper (Lemon’s dieback disease and little leaf disease), zinc (Khaira disease of paddy), manganese (Marsh disease of pea and phagla blight disease of sugarcane), sulfur (Tea yellow disease), boron (Fruit cracking in tomato and rough skin of guava and citrus), potassium (Marginal leaf drying in rice), calcium (Blossom end rot in tomato)

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