It's an overview about most prevalent plant disease attack on seedlings .the disease incidence is dependent more upon the conditions under which the seedlings are grown than upon the particular species of plant concerned.
2. Contents:
Introduction
Causal agents
Disease attacks to
Life cycle
Stages
Symptoms
Causes
Control
Management
Other tips and suggestion
3. Introduction:
Fungi usually just at the soil level on to hypocotyl or upper taproot
causing partial or complete rot and the seedlings suddenly topple over in
a characteristic manner.
Of the various species of soil-inhabiting fungi responsible for damping-
off of seedlings, Pythium debaryanum ranks first in importance, in
relation to this disease as a damping-off parasite.
FIRST STUDIED by : Hesse in 1874
De Bary in 1881
4. CAUSUAL AGENTS :
A number of different fungi and fungi-like organisms cause the symptoms of damping off, including:
Alternaria species. Cause leaf spotting.[2]
Botrytis cinerea – also known as "grey mould". Symptoms caused by this often accompany other
symptoms.[2]
Fusarium species.[1]
Macrophomina phaseoli – a plant pathogen that causes charcoal rot on many plant species
including Zea mays and Pinus elliottii.[citation needed]
Phyllosticta species. Cause leaf spotting.[2]
Phytophthora – a genus of plant-damaging oomycetes (water molds), whose member species
are capable of causing enormous economic losses on crops worldwide, as well as environmental
damage in natural ecosystems.[3]
Pseudomonas species. Cause leaf spotting.[2]
Pythium – a genus of parasitic oomycete. Once classified as fungi, and consequently sometimes
still treated as such. Along with Rhizoctonia solani, attacks by Pythium are most associated with
producing roughly circular patches of dead seedlings.[2]
Rhizoctonia solani – a plant pathogenic fungus with a wide host range and worldwide
distribution.[3]
Sclerotium rolfsii – a corticioid fungus in the family Atheliaceae. It is a facultative plant pathogen
and is the causal agent of "southern blight" disease in crops.[4][5]
Thielaviopsis – a small genus of fungi in the order Microascales. The genus includes several
important agriculturalpathogens.[6][7]
5. Identification of Damping Off
Disease
Identification of this disease is easy.
Seedlings, which were previously healthy, fall over. They do so, right at the soil level.
You might not see the fungus at first. As the disease progresses, this white cottony
fungus is clearly visible on top of the soil. As days, go by it, quickly worsens.
6. Disease attacks to :
Almost any kind of plant may be attacked by damping-off fungi while in young,
tender, succulent stage of development. But the disease incidence is dependent
more upon the conditions under which the seedlings are grown than upon the
particular species of plant concerned.
9. SYMPTOMS :
All symptoms result in the death of seedlings
Circular patches
Stem lesions at ground level
Stem of seedling may also become thin and tough
Leaf spotting
Grey mold growth on stem and leaves
Roots sometimes rot completely
Discolored stumps
Low rate of germination
Seedlings to topple
White/pink /grey cottony fungus
14. CAUSES :
• Abundant moisture
• Fairly warm temperature
• Lack of aeration of the surface soil
• Too much shade
• Thick sowing in seed bed
• Water logging
• Soil temp 20`C – 28`C are ideal for host infection by direct penetration
• Enzymes secreted by pathogens
1. Pectinolytic
2. Proteolytic
3. Cellulolytic
15. CONTROL
Since the fungus responsible for causing damping-off trouble is soil- borne and
since the temperature and moisture factors of the environment play important role
in determining the severity of infection, control measures are largely based on:
(i) Proper seed bed soil preparation
(ii) Soil treatment
(iii) Seed treatment
(iv) The manipulation of watering system
(v) Application of improved cultural practices.
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20. Controlling of damping-off disease
Do
** Buy sterilized seed
starting soil.
** Use clean, sterilized
containers.
** Provide plenty of air
circulation.
Tip
Use a small fan and direct a very
gentle breeze across the plants.
The important word here is
"gentle", as seedlings are delicate.
** Thin seedlings to increase air
circulation.
** Provide as much sunlight as
possible.
** Let the surface of the soil dry
out between watering. Watering
from the bottom is much
preferred.
** Stir the top of the soil around
the seedlings.
** Put plants in a sunny location. It
helps to keep the surface soil dry.
Don’t
** Don't leave your seedling
trays in the basement.
Basements are perfect
breeding grounds for molds
and fungus..
** Don't overwater plants.
** Do not use fertilizer on
your new seedlings.
** Don't use tray covers.
While it is a popular practice
to use them, they increase
the humidity level, and
encourages disease growth.
21. Other Tips and Suggestions:
It is believed that soaking seeds in a small amount of water and a clove
of crushed garlic will prevent the disease.
Some people suggest misting the plant with Chamomile tea as a
preventative.
Some people suggest fireplace ash on the top of the soil.
Cinnamon also acts as a fungicide.
Sphagnum moss spread thinly on the surface of the soil.