Different types of disease symptoms Necrosis : It indicates t | Agriculture Exams Library
Different types of disease symptoms
Necrosis : It indicates the death of cells, tissues and organs resulting from infection by pathogen. Necrotic symptoms include spots, blights, burn, canker, streaks, stripes, damping-off, rot etc.
Wilt : Withering and drooping of a plant starting from some leaves to growing tip occurs suddenly or gradually. Wilting takes place due to blockage in the translocation system caused by the pathogen.
Die-back: Drying of plant organs such as stem or branches which starts from the tip and progresses gradually towards the main stem or trunk is called die-back or wither tip.
Mildew: White, grey or brown coloured superficial growth of the pathogen on the host surface is called mildew.
Rusts : Numerous small pustules growing out through host epidermis which gives rusty (rust formation on iron) appearance of the affected parts.
Smuts : Charcoal-like and black or purplish-black dust like masses developed on the affected plant parts, mostly on floral organs as inflorescence are called smut.
Blotch : A large area of discolouration of a leaf, fruit etc. giving a blotchy appearance.
White blisters : Numerous white coloured blister-like ruptures are surfaced on the host epidermis that forms powdery masses of spores of fungi. They are called white
blisters or white rust.
Colour change : It denotes conversion of green pigment of leaves into other colours mostly to yellow colour, in patches or covering the entire leaves.
(i) Etioliation:
Yellowing due to lack of light, (ii) Chlorosis:
Yellowing due to infection viruses, bacteria, fungi, low temperature lack of iron etc.
(iii) Albino:
Lack of any pigment
and turned into white or bleached
(iv) Chromosis:
Red, purple or orange pigmentation due to physiological orders etc.
Exudation : Such symptom is commonly found in bacterial diseases when masses of bacterial cells ooze out to the surface of affected plant parts and form some drops or smear, it is called exudation. This exudation forms a crust on the host surface after drying.
Overgrowth :
Excessive growth of the plant parts due to infection by pathogens.
Overgrowth takes place by two processes
(i) Hyperplasia :
abnormal increase in size
due to excessively more cell division
(ii) Hypertrophy :
abnormal increase in size or
shape due to excessive enlargement of the size of cell of a particular tissue.
Atrophy:
It is known as hypoplasia or dwarfing which is resulted from the inhibition of growth due to reduction in cell division or cell size.
Sclerotia:
These are dark and hard structures of various shaped composed of dormant mycelia of some fungi. Sometimes, sclerotia are developed on the affected parts of the plant. Presence of sclerotia on the host surface is specifically called a sign of disease rather than symptom.
