The following points highlight the thirty-one important symptoms of plant diseases. Some of the symptoms are: 1. Anthracnose 2. Blight 3. Callus 4. Cankers 5. Chlorosis 6. Curling 7. Damping-off 8. Die-back 9. Discolouration 10. Dwarfing 11. Edema 12. Elongated Internodes 13. Etiolation 14. Exudation 15. Fasciculation 16. Galls and Tumours 17. Mosaic 18. Mummification 19. Phyllody 20. Prolepsis and Others.
Symptom # 1. Anthracnose:
These are circular to angular or irregular spots occurring along the stems, petioles, leaf veins and fruits. The affected tissues are finally killed leaving behind characteristic lesions.
Symptom # 2. Blight:
Blight is a symptom in which the diseased plant is killed suddenly. The pathogen rapidly kills the foliage, blossom and other above-ground parts of the host.
Symptom # 3. Callus:
This is the outgrowth of tissues in response to wounding.
Symptom # 4. Cankers:
These are the necrotic lesions, developing in the cortical tissues of stem, leaves or fruits, ultimately resulting in the corky growths in the affected parts.
Symptom # 5. Chlorosis:
Under this symptom, the normal green pigments of the plant are destroyed and the tissue becomes yellow.
Symptom # 6. Curling:
Sometimes, the infection of the pathogen results in the abnormal bending of stem, leaves and shoots of the host. This symptom is called ‘curling’. It is actually due to the localized overgrowth of cells and tissues.
Symptom # 7. Damping-off:
In this symptom, the stem of young seedling is affected at the ground level. This results in the toppling down and ultimate death of young seedlings.
Symptom # 8. Die-back:
Twigs or branches start dying from the tip downward, providing them a burnt appearance in this symptom.
Symptom # 9. Discolouration:
The colour of the whole plant or several of its parts is changed under this most common symptom of the diseased plants. The usual process or colour change is from green to yellow to brown.
Symptom # 10. Dwarfing:
This is the subnormal development of most of the plant parts resulting in the reduction of the size of stem, leaves and ultimately the plant height.
Symptom # 11. Edema:
The eruption or swelling of the epidermal cells of the infected plant is called “edema’ or intumescence.
Symptom # 12. Elongated Internodes:
This is the abnormal elongation of internodes of the infected plant due to hypertrophy (increase in size of the individual cells) and/or hyperplasia (increase in the number of cells due to cell division).
Symptom # 13. Etiolation:
This is the under-development of chlorophyll in plants developing in insufficient light.
Symptom # 14. Exudation (Bleeding and Gummosis):
This symptom results in the exuding of fluids from the diseased tissues. If the thick discoloured fluid flows regularly from the diseased tissue, it is called bleeding. But if a gummy substance oozes out from the diseased tissue and dries as a hard gummy mass, it is called gummosis.
Symptom # 15. Fasciculation:
If several plant organs, such as stem, leaves, flowers and fruits cluster together around a common focus, the symptom is called ‘fasciculation’.
Symptom # 16. Galls and Tumours:
Hypertrophy results in the formation of some irregular-shaped galls ranging from a few mm to 2 or 3 cm. Relatively large, fleshy or hard galls are called ‘tumours’.
Symptom # 17. Mosaic:
Uneven development of chlorophyll resulting in light green patches alternating with dark green areas is the symptom called ‘mosaic’. Mosaic is usually the symptom of viral infection.
Symptom # 18. Mummification:
When fruits become dry due to rotting and form a dark, wrinkled, hard mass, the symptom is called ‘mummification’.
Symptom # 19. Phyllody:
When the infection results in the formation of floral parts (sepals, petals, stamens, etc.) into leaf-like structures, the symptom is called ‘phyllody’.
Symptom # 20. Prolepsis:
When there is a premature development of shoots from buds, the symptom is called ‘prolepsis’.
Symptom # 21. Rot:
When the infection leads to the disintegration of the affected tissues, the symptom is called ‘rot’. Based on its nature, it may be soft rot, hard rot, dry rot, black rot, white rot, etc.
Symptom # 22. Russetting:
When the infection leads to the formation of brownish, superficial roughening of the skin of tubers, fruits, etc., the symptom is called ‘russetting’.
Symptom # 23. Rust Pustules:
These are the small pustules of spores which may be erumpent or submerged, linear or circular, and are often surrounded by chlorotic areas. Rusty pustules may be yellow, light-brown, dark-brown or red in colour. Often formed by members of Uredinales (e.g. Puccinia), white rust is caused by Albugo while the red rust of tea is caused by an alga Cephaleuros virescens.
Symptom # 24. Scab:
When outgrowth of epidermal and cortical cells results in the formation of ulcer-like lesions on tubers, stem, leaves and fruits, the symptom is called ‘scab’.
Symptom # 25. Smuts:
These are the malformations, containing masses of spores which provide the colony a colour of deep brown or dark black to the affected parts, such as stem, leaves, inflorescence and rarely to the underground parts of the host plant.
Symptom # 26. Spots:
Spots are the necrotic symptoms of different shapes, sizes and colours. They may be isolated or may coalesce in the later stages.
Symptom # 27. Streaks and Stripes:
The streaks are the linear lesions which develop due to infection on the leaf blade, leaf sheath and stem. The enlarged streaks form stripes.
Symptom # 28. Variegation:
This is a pattern of white patches formed by the non-development of chlorophyll in certain cells of the host due to the infection of the pathogen.
Symptom # 29. Vein-clearing:
This is viral symptom developed due to the inhibition of chlorophyll formation in the veins of the host.
Symptom # 30. Wilting:
The drooping condition of plant resulting from the vascular infections of the roots and stem is called “wilting’.
Symptom # 31. Witche’s Broom:
When the infected branches of the host become abnormally erect, the symptom is called ‘witche’s broom’.