. Bacteria
2. Fungi
3. Virus
4. Nematode
1.
Bacteria: These are
micro-organisms which can not be seen with naked eye unless we use a powerful
microscope. Bacteria are found every when even under a condition where other
living organism cannot exist such as in water in soil in the air in plant in
animal, etc
Bacteria:
These are
useful to man in the following ways:
i.
The help in the decomposition
of compost and organic materials.
ii.
They are useful in the
fermentation process e.g. production of drinks such as beer, wine, etc.
iii.
They are also useful in the
making of cheese.
iv.
They also help to fix
atmospheric nitrogen into the nodules of legumes..e.g Azotobacter,
Nitrosomonas.
On the other hands, bacteria causes crop disease which are
transmitted from one plant to another by
wind, rain splash and by insects.
Examples, of such disease include the following Bacteria Blight of Cotton, Bacteria Blight of Guinea Corn,
Examples, of such disease include the following Bacteria Blight of Cotton, Bacteria Blight of Guinea Corn,
Bacteria Wilt of tomatoes.
2.
Fungi: These are also microscope
organism and they are regarded as plant but they do not process chlorophyl root,
stem and leaver. But they leave as parasite on plant and transmitted of disease
or diseases e.g. maize, smut, leave rust or leave spot, black pour, of cocoa,
damping off, can be transmitted by wind , rain splash , by insect, etc.
3.
Virus: These are microscopic organism, smaller than Bacteria and
Fungi.They can only be seen under very powerful microscopic or electronic
microscopic. They cause serious and civil diseases in crop plant. Virus
diseases are transmitted by piercing and sucking insects. Disease cause by
viruses include Coca Swollen Shoot, Groundnut Rosette, Cassava and Yam Mosaic, etc.
4.
Nematode: These are soil born organism.
They are worm like animals. Many of them live on dead organic matter while
others live as parasites on plants. Some are microscopic while others are big enough to be seen with naked eye. The
parasitic nematode attack plant hosts
and caused diseases such as Tuber rot,
Root knot, Die back, etc.
SIGNS
AND SYMPTOMS OF CROP DISEASES
1.
Yellowing and wilting of plants
leaves
2.
Curling, twisting and winkling
of leaves.
3.
Stunted Growth.
4.
Rottening of leaves, stems and roots.
5.
Defoliation of plants
6.
Brown patches with spots showing dead areas on leaves.
7.
Mouldy grains.
8.
Death of Plants
9.
Reduced product quality.
1. Low Yield.
EFFECTS OF DISEASES ON
CROP
1.
Poor yield
2.
Low quality and loss of market
value.
3.
Delayed maturity.
4.
Death of crops
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