3. What is plant disease??
Definition of Plant disease
An impairment of the normal state of the plant that modifies
its vital functions
The organism that cause disease are called pathogens e.g.
bacteria ,viruses ,protozoa etc.
The study of disease condition is called pathology
4. Healthy plant
Sick/ diseased plants
Difference between healthy and
disease plant
Normal physiological
functions e.g.
Normal cell division
,differentiation and
development
Absorption of water and
minerals from
the soil and translocation
Photosynthesis
Reproduction
A plant would not have all these
functions
5. Classification on the basis of
cause
Infectious disease
A disease that is caused by pathogen which spread from
diseased plant to a healthy plant
Non infectious disease
Disease which that is caused by non living organisms
6. On the basis of occurrence and
geographical distribution:
Endemic
e.g. wart disease of potato
Epidemic
e.g. rust, mildews
Sporadic
e.g. leaf blight
10. Blight disease
Blight is generally a plant infection caused by a pathogenic
organism. It caused browning, yellowing,
withering followed by the death of plant tissues. Plants
attacked by this disease also show discoloring of stems,
fruits and leaves. Plant blight is caused by a bacteria or
fungus. irregular dead areas on various parts of a plant which
is called the blight.
11. Mildew disease
Mildew is a specific kind of mold, usually with a flat growth
habit. this is commonly produced by fungi.
It is of two types:
Powdery mildews
Downy mildews
12. Downy mildew
Foliage habitat
produced in the severe conditions when the water film is
present , the relative humidity, and cool and hot environment.
13. Powdery Mildew disease
Obligate parasite
Produce patch and spots on plants in the form of powder in
plant tissue and leaves.
Produce the conidiophores on plant surface.
15. Rust:
Pathogen of puccinia
It is spread by spores by the infected to healthy plant.
Formation of pustules on each leaf blade.
Two hosts
16. smut
Mainly affeacted the wheat, sugarcane.
Ustilogo is the genus of smut.
Produced the black spores .
Anthoceious life cycle.
Spores dispersed by wind,insects or by water.
17. Rot
caused by fungi, bacteria and fungus like organisms.
causes the decay roots, stems, wood, flowers, and fruit.
symptoms produced leaf spots and blights.
18. canker
Destructive to wide range of trees and shrubs.
Usually kill and branches and infected areas.
Mostly occur in citrus family.
Xanthomonas citrus
27. Parasitic disease:
Disease due to casual agencies( fungi, viruses Bacteria etc.)
Some members which effect trees are:
Viscum album ( semiparasites)
Cuscutta spp (leguminous plants)
Striga spp (root parasites)
Cephaleorus spp (on angiosperm)
Toxicogenic insects(insect damage plant by sucking,chewing
and show the same symptoms as fungi)
28. Non parasitic disease
Disease due to non parasitic casual agencies.
Agencies are as follows:
Soil moisture disbalance
Nutritional disorder
High or low temperature effect
Effect of light
29. Symptoms due to soil moisture
imbalance:
Wilting: drooping of leaf or stem tips.
Blast: sudden death of young bud inflorescence or young
fruit.
Scorch: sudden death of leaves and fruits
Firming: drying and dying of leaves specially in grass maize
and tobacco.
Die back: dying backward from the twigs or tips of branches.