SYMPTOMS OF PLANT DISEASES

Any change external or internal in the host plant which serves to recognize the disease is called symptoms. The most important type of symptoms is as follows.

I. Necrosis: It includes death of the infected tissues. The different necrotic symptoms are as follows.

1. Wilts: In wilts, the host plant loses water and gets dehydrated.
2. Damping off: The tissues at the base of the stem in young seedling collapse and degenerate leading to their death in this region.
3. Rot: In rot, the affected tissues are completely disorganized leading to their death in this region.
4. Streak or Stripes: In stripes, the affected tissue appears in the form of elongated and narrow lesions.
5. Canker: canker is the sunken necrotic lesions developed in cortical tissue of stem, leaf and fruit.
6. Spot: Spot is produced due to death of localized region in the root, stem or leaf.
7. Blight: Blight is the burnt appearance due to sudden death of a plant or its organ.
8. Die-back: It is charaterised by dying of plant organs, especially stem or branches, from tio backwards.

II. Hyperplasia (Hypertrophy): It includes increase in cell division or increase in cell size leadind to outgrowth. The different hyperplasia symptoms are as follows;

Galls: Galls are globose, elongated or irregular malformation or outgrowth developed on the affected part of the host plant. Small galls are called warts or tubercules, while larger one are called knots.
Pocket or Bladder: Bladders are formed when the affected fruit is considerably enlarged, distorted and often hollowed to form pockets.
Curl: Curl is formed due to hypertrophy in localized area of the leaf.
Witches broom: It is closely grouped clusters of fine slender braches generally arranged parallel to one another.
Floral abnormalities: The floral parts of some host plants are enlarged and become fleshy and leaf like due to the infection of certain fungi.

III. Hypolysia (Dwarfing or atrophy): This is the reduction in the size of plant parts. The different dwarfing is as follows:
Chlorosis: Poor development of chlorophyll leads to chlorosis. It is caused due to low temperature, mineral deficiencies or certain infections.
Variegation: It is appearance of white or yellow spot in the green chlorophyllous region of the infected leaves.
Stunting: It is caused due to stunting growth leading to dwarfing.
Mosaic: It is development of light green or yellow patches with dark green pathches.
Rossetting: It is caused due to shortening of the internodes of shoot. It leads to crowning of the foliage in cluster assuming in rosette form.
Vein-clearing: It is caused due to yellowing of tissue near the vein.