Topic: Crop Plant Diseases
Generally disease can be defined as an infection or unfavourable condition caused by living organisms (pathogens) or non-living things expressed in characteristic conditions known as symptoms and harmful to the organism or its parts or it may simply reduce the market value.
A plant disease may be defined as a departure or deviation of the plant from the normal state of health, presenting marked symptoms or outward visible signs. In other words, disease is an unfavourable condition caused either by the pathogens present within a living organism or by nutritional deficiency. It usually results in physiological and anatomical abnormalities expressed in characteristic symptoms. The harmful effects of a disease to the plant or to any its parts and products generally result in the reduction of the economic value of the plant.
Causes of Diseases
The primary causes of diseases can be classified into two groups, pathogens and pathological factors.
- Pathogens – Theses are disease inducing living organisms or agents which pass through a regular cycle of development and reproduction. Examples are – Viruses, Bacteria, Fungi and Nematodes.
- Physiological Factors – They may be physical, chemical or environmental. Many of them are essential for normal growth of plants, but when they are deficient or present in excess, they cause diseases. These are factors which are essential for normal growth and development of plants. Excess or deficiency may cause diseases. Examples are
a – Nutritional deficiency
b – Heat
c – Inorganic salts
d – Water
Classification of Plants disease
The disease spreads through seed, soil, or through wind. Plant disease may be grouped as
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