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A plant disease, also known as phytopathology, is a pathological condition or ailment that interferes with a plant’s natural growth, development, or functioning. Pathogens (such as fungi, bacteria, viruses, and nematodes), environmental stresses (such as severe temperature, drought, or pollution), and even dietary imbalances can all cause these disorders. Plant diseases can harm plant health by causing observable symptoms, diminished growth, and, in extreme situations, the loss of plant parts or entire plants. These diseases can have a considerable impact on crop yield, biodiversity, and general plant health in agriculture, horticulture, forestry, and natural ecosystems. Effective plant disease management and control are critical for sustainable agriculture and ecosystem health.

Different Disease Symptoms in Plants

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 and inflorescence are called smut.

Blotch: A large area of discoloration 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:Exudation is a typical sign of bacterial illnesses in which masses of bacterial cells flow out to the surface of afflicted plant parts and form drips or smears. After drying, this exudation produces a crust on the host surface.

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, rigid structures of diverse shapes made up of latent mycelia from various fungi. Sclerotia might develop on the afflicted portions of the plant. The presence of sclerotia on the host surface is referred to as a marker of disease rather than a symptom.

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