Soil and environmental. Phytopathology

Introduction,
Classification,
Pathogens,
Distribution

1. VIVEKANANDHA ARTS AND SCIENCE COLLEGE FOR WOMEN
VEERACHIPALAYAM, SANKAGIRI, SALEM, TAMILNADU
SUBJECT:SOIL AND ENVIRONMENTAL MICROBIOLOGY
DEPARTMENT OF MICROBIOLOGY
SUBMITTED BY
M. JAMINA
M.SC MICROBIOLOGY
VIVEKANANDHA ARTS AND SCIENCE
COLLEGE FOR WOMEN, SANKAGIRI,
SALEM, TAMILNADU
SUBJECT INCHARGE
Dr. R.DINESHKUMAR,
ASSISTANT PROFESSOR,
DEPARTMENT OF MICROBIOLOGY,
VIVEKANANDHA ARTS AND SCIENCE
COLLEGE FOR WOMEN. SANKAGIRI,
SALEM, TAMILNADU
TOPIC:PHYTOPATHOLOGY

2. CONTENT:
•Definition
•Classification
•Pathogens
•Distribution
•Characteristics
•Disease Cycle
•Prevention &control

3. Phytopathology
Definition
Plant pathology or phytopathology is the science, which deals with the
plant diseases.
Phytopathology (Greek Phyton = plant + pathos – disease, ailments + logos
= discourse, knowledge) is the branch of agricultural, botanical or
biological science which deals with the cause, etiology, resulting in losses
and management methods of plant diseases

4. The most well-known leaf spot disease is that of Arachis
hypogea L. (groundnut). Generally, so it is called the tikka
disease. The tikka disease is a dangerous disease in
areas where the groundnut crop is grown in India.
The spots take place on the host leaves when the plants
are one or two months old. Later, necrotic lesions also
appear on the stem. There are two leaf spot diseases of
groundnut due to two different species of the genus
Cercospora.
Groundnut: Tikka disease

5. Classification:
Kingdom: Fungi
Phylum: Ascomycota
Class: Dothideomycetidae
Order: Capnodiales
Genus: Cercospora
Pathogen
Cercospora personata
Cercospora arachidicola
Distribution: The genus Cercospora can be
found widely in the tropical part of the world.
Especially in countries where the groundnut crop
production is more.

6. Characteristics of Pathogen
Cercospora arachidicola
The appearance of Cercospora arachidicola is dark brown and it grows
intracellularly in plant tissue.
Haustoria absent in Cercospora arachidicola.
The conidiophore of Cercospora arachidicola appears as continuous,
unbranched, yellowish-brown, geniculated, and septate (1-2 septa present).
The conidia of Cercospora arachidicola are long, cylindrical, hyaline, and septate
(1 to 12 septa). Truncates at the base and sub-truncates at the apex.

7. Cercospora personata
The appearance of Cercospora personata is brown-black and primarily
grows intercellularly and after a certain period grows intracellularly.
Branched haustoria are found in Cercospora personata.
The conidiophore of Cercospora personata appears as continuous,
unbranched, light brown, geniculated, and aseptate.
The conidia of Cercosora personata are short, cylindrical, wide, and
septate (3 to 4 septa). Rounded at one end and tapered at the other end.

8. Cercospora arachidicola

9. Cercospora personata

10. Leaf spots are small, round, and about 1-6 mm in diameter.
The necrotic lesions appear on the surfaces of two leaves and change from
dark brown to dark in color.
The lack of bright yellow light in young spots, however, develops around the
older ones.
The mycelium consists of hyphae which are entirely internal.
Symptoms

11. The unbranched conidiophores grow in tufts from a dense, globular, and brown to
black stroma (23-30 µ in dia.) and emerge by rupturing the host epidermis.
The conidiophores are determinate to the lower surface of the host leaf and are
seen arranged in concentric circles in the tuft.

12. Disease cycle

13. The pathogen penetrate through conidia on diseased plant debris lying in the ground.
The conidia may also adhere to the shell. They have also been found to be associated
with the seeds and are responsible for early infection.
A temperature that ranges from 26°C. To 31 °C. With high atmospheric humidity is helpful
for disease development.
Prolonged low temperature and dew also favor infection. The penetration of the pathogen
in the host tissue takes place either by direct penetration through the epidermal cells or
through the stomata.
The disease is propagated by the wind which blows the conidia from leaf to
leaf. So, insects and plumps of rain have also been reported to play role in the
dissemination of the disease.

14. Control measures
Rotation of crops, seed treatment, and disposal of infected host debris by
burning or burying in deep holes eliminates the possibility of early infection from
the soil growing in the inoculum.
The seeds within the shells are sterilized with sulphuric acid.
The only remedy is to check the secondary spread of disease in the field and
spray with suitable fungicides. The use of the Bordeaux mixture has given good
results among the fungicides.
The yield of sprays of these fungicides has increased by as much as 100%. Early
mature varieties were known to be resistant to disease.

15. CONTENT:
•Definition
•Classification
•Distribution
•Impact
•Symptoms
•Spread
•Disease cycle
•Control measure

16. Citrus canker
Citrus canker is a disease caused by the bacterium Xanthomonas
citri subsp. Citri (synonym X. Axonopodis pv. Citri).
It thrives in areas with high rainfall and warm temperatures.
Citrus canker is found throughout Florida and in limited areas of
Alabama, Louisiana, and Texas.
Severely infected citrus trees may lose their leaves and prematurely
drop fruit.
Canker-infected fruit is safe to eat but is not marketable due to its
appearance.
Definition

18. A very well-known and wide spread disease in all Citrus
producing areas of the world. It
is quite serious disease in countries like India, China, Japan and
Java. According to Fawcett,
bacterial canker had its origin in India. From where it spread to
the rest of the world. The disease
was eradicated in the USA at a cost of several million dollars by
destroying millions of diseased
trees to kill the bacteria. Strict quarantine regulations were then
established to prevent its re-entry
into the USA.
Distribution

19. Symptoms of citrus canker
Disease begins as small pimple-like spots that are about 1 mm in diameter
and yellow in colour. As the spots enlarge, they become brown and corky with
sunken centres and raised edges. Often each of these spots have a yellow ring
surrounding them.
Impact
Citrus canker decreases fruit quality and yield. The
disease leads to defoliation, twig dieback, blemished fruit
and premature fruit drop. In severe cases, it can cause tree
death.

21. Spread
The canker lesions ooze bacteria when wet, which can infect new growth,
and be dispersed over short distances through wind, rain splash and
overhead irrigation.
Long distance spread can occur through flooding and cyclones, and human
assisted movement of clothes, equipment and infected plant material
(including budwood, rootstock seedling, budded trees).
Plants are infected when bacteria or bacteria spores enter wounds and
natural openings on leaves, growing shoots and fruit. The disease can be
spread by birds, insects and humans, particularly when trees are wet.
The bacteria can survive in diseased plant tissue as well as in soil. It can
over-winter in angular shoots, and then become active again the following
season.

23. •Control measures
•
•Very difficult to control.
•Only practical method is destruction of the diseased plants by
burning them.
•Use of disease free nursery stalk.
•Spraying of 1% bordeaux mixture before planting in new orchards.
•In old orchards, pruning of the affected twigs, Spraying of 1%
bordeaux mixture at periodical intervals especially rainy season.
•Burning of dropped of leaves and twigs.
•The vigour of the plant should be maintained by proper irrigation
and fertilization.
•Proper care given to minimize the attack of leaf miners.
•Rigidly follow quarantine measures.
•Development of resistant varieties

24. Thank you