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 TOPIC:   DISEASES OF CROPS
CONTENTS: (a) Meaning of diseases
(b) General effects of disease on crop production
(c) Diseases of major crops
 Sub-topic 1:
Meaning of Disease: A disease is a departure from normal state of health, presenting marked symptoms or outward visible signs. OR
A disease is a condition of disorder in the functioning of the tissues of an organism.
It is an unfavorable condition caused by infections by pathogens or deficiency or excess of some environmental factors which result in physiological and anatomical dysfunctions expressed in characteristic symptoms.
Diseases of major crops
(i) cereals – smut, rice blast, etc.
(ii) Legume-cercospora leaf spot, rosette, etc.
(iii) Beverages-cocoa black pod, coffee leaf rust, etc.
(iv)Â Tuber-cassava mosaic, bacterial leaf blight, etc.
(v)Â Fruits- citrus Gummosis, Diebacks etc.
(vi)Â Fiber-Black arm (bacterial blight of cotton.
(vii)Â Vegetables-root knot of tomato or okra etc.
(viii)Â Stored produce-mould.
causes of Diseases.
- Pathogen Diseases: These are diseases caused by living microorganisms called pathogens. e.g
- Bacteria
- protozoan
- Fungi
- Viruses
- Nematodes
- Environmental Diseases: These are sometimes called physiological diseases. They may be caused by the following.
- Excess or deficiency of some nutrients
- Excess of water which hinders proper respiration and absorption of nutrients
- Lack of water which result in wilting
Examples of environmental diseases
- Wilting
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