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» Introductory Plant Pathology
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Current Category » Crop Disease and Management

Symptom Caused by Phytopathogenic Bacteria

1. Local Lesions:

Localised spots may occur on the leaf blade, petiole, stem and fruits. The leaf spots starts as minute water soaked specks, spreading rapidly to form circular, irregular or angular spots, bound by veins and veinlets. The pathogen which enters the host tissues through stomatal openings establishes in the substomatal space and remains so in the parenchymatous tissues causing necrotic lesions.

E. g Angular leaf sop of cotton caused by Xanthomonas campestris pv. malvacearum.

2. Blights:

The invasion by the bacterium loads to very rapid and extensive necrosis of the affected plant parts resulting in scorched appearance of the host.

E. g Bacterial blight of paddy caused by Xanthomonas campestris pv. oryzae.

3. Soft Rots:

The soft rot symptoms are found mainly on fleshy parts. The major effect is softening of the tissues due to disintegration of cells and dissolution of middle lamella, as a result of enzyme action. Very often a dirty liquid oozes out of the affected parts. In many causes, the disintegration is preceded by change of colour.

E.g Black leg and soft rot of potato caused by Erwinia carotovora sub species carotovora and Erwinia carotovora sub species atroseption.

4. Tumors and Galls:

In many bacterial diseases the effect of invasion by the pathogen is hyperplasia and hypertrophy of invaded tissues. As a result, tumours develop on the affected organs.

E. g Crown gall tumors on rose plant caused by Agrobacterium tumefaciens.

5. Vascular Disease:

In same of the bacteria leaf spot diseases the organism moves into the vascular system and becomes systemic. In others, the invasion is concentrated in the vascular tissues causing typical wilt of the plant by plugging the water conducting vessels and by production of toxins.

E.g Bacterial canker and wilt of tomato caused by Clavibactor (Corynebacterium) michiganese sub species michiganese. Bacterial wilt of tomato, potato, tobacco and egg plant caused by Pseudomonas solanacearum.

6. Scabs and Cankers:

Scabs and cankers are corky outgrowth which is formed on leaves, twigs and all other plant parts above the ground. These outgrowths are the result of the reactions of the host tissues to the pathogen. Such reactions are mostly localised and often confirmed to the parenchymatous tissues of the host plant. Scab is formed by epidermal infection and is not deep seated. Cankers on the other hand, are deep seated and involve the cambium layer.

E. g 1. Citrus canker caused by Xanthomonas Campestris pv. citri.
2. Common scab of potato caused by Streptomyces scabs.

Current Category » Crop Disease and Management