This document discusses the causal organism, symptoms, and management of damping off disease in tobacco caused by Pythium aphanidermatum and Pythium debaryanum. It describes the pathogens as soil-borne oomycetes that cause pre- and post-emergence damping off in tobacco seedlings. Symptoms include water-soaked lesions on stems near the soil surface and rotting of the stem. The disease is favored by high soil moisture, low temperatures, and overcrowding. Management strategies include cultural controls like sanitation and spacing, as well as fungicide drenches and foliar applications of copper-based products.

1. STUDENT: COURSE TEACHER:
LAVANYA.A.L Dr. S. PARTHASARATHY
ID. No. 2016021020 Asst. Prof., (Plant Pathology)
COLLEGE OF AGRICULTURAL TECHNOLOGY
Affiliated to Tamil Nadu Agricultural University, Coimbatore
Kullapuram, Via Vaigai dam, Theni-625 562
DAMPING OFF OF TOBACCO

2. CAUSAL ORGANISMS
• Pythium aphanidermatum (Edson)
• Pythium debaryanum2

3. COMMON NAMES
• Pythium rot
• Stem rot
HOSTS
• Soyabean
• Beets
• Cucurbits
• Cotton

4. DISTRIBUTION
• O Occurs worldwide in greenhouses and field
systems . Globally , this pathogen is present in
tropical regions.

5. HISTORY
• Mathews (1931) did much work to clarify the
taxonamic position of the known Pythium spp.,
during his time.
• Middleton (1943) compiled an extensive
monograph of the genus Pythium.
• Waterhouse (1967, 1968) compiled the original
descriptions and illustration of the species and
published a key to the genus in 1967.
• Literature up to 1961 has been compiled by
Rangaswamy (1961).

6. SIGNIFICANCE
• This pathogen is economically important in crops
that are produced both in greenhouse and soil-less
culture.
• Root infection and damping off are responsible for
a decrease in plant health and reduction in yield
for economic crops such as corn, cotton and beets.
• It causes several losses in nuseries where young
suspectible transplants are produced.

7. SYMPTOMS
• The pathogen attacks the seedlings at any stage in
the nursery.
• It is a serious problem in tobacco nuseries both in
heavy clay soils and light sandy.
• Maximum damage 5-6 weeks after sowing.

8. DISEASE IS NOTICED IN TWO PHASES
Pre emergence damping off
• Seedlings are infected which die before emergence
from the soil resulting in poor and uneven stand of
the seedlings.
• Water soaked minute lesions appear on the stems
near the soil surface, soon girdling the stem,
spreading up and down in the stems and with in
one or two days stem may rot leading to topping
over of the seedlings.

9. Post emergence damping off
• The young seedlings in the nursery are killed in
patches and infection spreads quickly. Under the
favourable conditions, the entire seedlings in the
nursery are killed within 3-4 days.
• A thick weft of mycelium may be seen on the
surface of the soil.
• Post emergence damping off is the most
destructive phase.

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11. DAMPING OFF OF TOBACCO
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13. PATHOGEN
• Anamorph : Pythium aphanidermatum
• Teleomorph : Pleospora bjoerlingii
• Author : (Edson) Fitzp.

14. SYSTEMATIC POSITION
• Kingdom :Chromista
• Phylum :Oomycota
• Class :Oomycetes
• Order :Peronosporales
• Family :Pythiaceae
• Genus :Pythium
• Species :P. aphanidermatum

15. PATHOGEN CHARACTERS
• P. aphanidermatum is a soil-borne pathogen
belonging to fungus like organisms Oomycetes.
• It is a fast growing and produces white, cottony
mycelium on Potato Dextrose agar medium.
• Main hypha lack cross-walls and measure up to
10μm wide.

16. • P. debaryanum is a species of water mould in the
family Pythiaceae. It is known as a plant pathogen
on many kinds of wild and cultivated plants
including peanut, beet, eucalyptus, tobacco and
pine trees.
• The plants develop damping off , a disease state.

17. LIFE CYCLE
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18. MODE OF SPREAD
• The fungus survives in soil as Oospores and
Chlamydospores.
• Primary spread - soil – borne fungal spores.
• Secondary spread - sporangia and zoospores
transmitted by wind and
irrigation water.

19. FAVOURABLE CONDITIONS
• High soil moisture
• Low temperature (below 24º C) and low soil
temperature of about 20 º C
• Over crowding of seedling
• Ill drained nursery beds
• Heavy shade in nursery
• High atmosphere humidity (90-100%)

20. MANAGEMENT
CULTURAL CONTROL
• Proper sanitation can greatly reduce the risk of
infection by P. aphanidermatum.
• Use of clean pots, media and plant material can
help to prevent the infection of plants by the
fungus.
• Proper air circulation between plants can make
conditions less favourable for disease
development.
• Poor drainage is a contributing factor to the
dispersal of Pythium, as with other water fold
fungi.

21. BIOLOGICAL CONTROL
• There is no biological control methods at present
on the market. Some writers recommened the
inoculation of seed with spores of Penicillium sp.
or Trichoderma viride, which are also fungi but
hostile to damping off disease ones.

22. CHEMICAL CONTROL
• Soil drenches of many fungicides are effective in
controlling P. apanidermatum.
• Metalaxyl (Subdue and Ridomil Gold) can be
sometimes used.
• Spray the nursery beds two weeks after sowing
with 1% Bordeaux mixture or 0.2 % copper
oxychloride or 0.2% Mancozeb and repeat
subsequently at 4 days interval under dry weather
and at 2 days interval under wet cloudy weather .

23. REFERENCES
• Rangaswami.G., Mahadevan.A., Diseases of Crop
Plants in India. PHI Learning Private Limited, Delhi.
• Agritech.tnau.ac.in > tobacco_d1
• Vikasepdia.in > ipm-strategies-for-tobacco
• Eagri.org > PATH272 > lecture08