The document discusses the role of studying disease cycles in plant disease management. It provides examples of disease cycles for several plant diseases like sheath blight of rice, wheat leaf rust, bacterial leaf streak of rice, stem rust of wheat, loose smut of wheat, and club root of cabbage. For each disease, it summarizes the stages in the disease cycle and how interrupting different stages can help manage the disease, such as removing alternate hosts, applying fungicides at the right time, and crop rotation. Understanding disease cycles is important for developing strategies to control diseases by breaking the cycle.

1. SEMINA
R-ICourse No: PPA-591
Topic; ROLE OF DISEASE CYCLE STUDY IN
MANAGEMENT OF PLANT DISEASES
Chairman: Dr Dilip
Kumar MisraSeminar
leaders :
Prof. Srikanta Das & Prof.
Amitabha BasuM . Sc(Ag) (3rd Semester) 2nd
YearDepartment Of Plant Pathology ,
BCKVMohanpur,
Speaker : Konjengbam. Sarda Devi

2. INTRODUCTION
 A disease is an interaction amongst the host, parasite, environment
and time.
 Understanding the factors that trigger the development of plant
disease is essential to create and implement effective strategies for
disease management.
 The description of the disease cycle is the foundation of plant
disease epidemiology and key for developing effective disease
management.
 Studying the role of disease cycle will enable us to learn the
various weak points to interrupt and reduce the severity of the
disease or prevent the disease.
 Here we illustrate the role of disease cycles study in plant
disease management.

3. What is a disease cycle ?
 Disease cycle is the sequence of progress in disease
development from the initial contact between a pathogen and
its host to the completion of the syndrome.
 It is the series of events involved in disease development,
including the stages of development of the pathogen and the
effect of the disease on the host.
 Events involved in disease cycle: 1) inoculation
2) penetration
3) infection
4) growth & perennation
5) dispersal
6) survival

4. A GENERALISED DISEASE CYCLE

5. Components of the disease cycle
DORMANCY/
PERENNATION
REPRODUCTION DISPERSAL
RELEASE
TRANSPORT
SURVIVAL
DEPOSITION
PATHOGENESIS
PENETRATION
INFECTION
INCUBATION
SYMPTOM
EXPRESSION

6. SCHEMATIC REPRESENTATION OF INTERRUPTION
OF DISEASE CYCLE – TARGET AT INOCULUM
Survival Inoculum
produced
Dispersal
Colonization
Symptoms
Production of survival
structure
Infection

7. SCHEMATIC REPRESENTATION OF INTERRUPTION DISEASE
CYCLE AT THE POINT OF INFECTION
Survival Inoculum
produced
Dispersal
Colonization
Production of
survival structure
symptoms
Infection

8. How different stages of disease cycle are
interrupted for plant disease management ?
DORMANT STRUCTURES/PERENNATION:
Methods of eradication like temporary
removal and destruction of host plant or
roguing, sanitation of equipment and storages,
and chemical treatment of soil or seeds where
dormant structures of pathogen perpetuates
can reduce inoculum population.

9. DISPERSAL OF INOCULUM:
PATHOGENESIS:
The disease cycle study has illustrate the penetration and
colonization of pathogen can be interrupted and
interruption can be created through prophylactic or
protection for which the correct timing of chemical
applications as well as choosing the proper chemical is
essential for good control.
Almost all dissemination of pathogens responsible for
plant disease outbreaks is carried out passively by
agents such as water, air and insects, thereby
management of irrigation water, air through wind break,
insect and other vectors are to be followed carefully.

10. Disease management

11. CASE STUDIES
e
SHEATH BLIGHT OF RICE

12. DISEASE CYCLE OF SHEATH BLIGHT OF RICE AND
ITS MANAGEMENT
CYCLE:
The pathogen can survive as sclerotia or mycelium in dry soil for
about 20 months and in moist soil for about 5-8 months.
 The sclerotia spreads through irrigation water.
 The fungus comes in contact with a healthy plant and grows in it
causing the disease.
Management:
 From the disease cycle study, it is clear that fungus survives as
sclerotia as a source of inoculum and disseminates through irrigation
water hence the flow of irrigation water should be avoided form
diseased to healthy field.
 Deep ploughing in summer and burning of stubbles can reduce the
inoculums load.

13. WHEAT LEAF RUST CYCLE

14. DISEASE CYCLE OF WHEAT LEAF RUST AND ITS
MANAGEMENT
CYCLE
In early January, the rust gets well established in the foot hills of Himalayas
and also in the plains of Tamil Nadu and Karnataka in the south.
MANAGEMENT

15. BACTERIAL LEAF STREAK OF RICE

16. CYCLE:
 The pathogen can survive in infected seed but not in crop debris.
 The bacteria enter the leaves through stomata and wounds.
 When the leaves are wet, exudate from infected leaf spread to
other portions of the leaf and to other plants.
 Rain, storms and typhoons favour the spread of the disease.
DISEASE CYCLE OF ‘BLS’ OF RICE AND ITS MANAGEMENT
MANAGEMENT:
 From the above illustrations of the disease cycle, it is clear that
wounds, clippings of tips of seedlings at the time of transplanting
should be avoided.
 Since the pathogen can survive in the seed, seed treatment
eradicates the seedling infection.
 Spraying with streptocycline (250ppm) along with copperoxy-
chloride (0.3) is recommended for protection.

17. STEM RUST OF WHEAT

18. CYCLE:
 The fungus over summers on the wheat plants and grasses in the
hilly areas and spreads to the plains in the main wheat crop
season.
The grasses, viz., Briza minor, Bromus patula, Brachipodium
sylvaticum and Avena fatua, harbor the fungus in the off-season.
DISEASE CYCLE OF STEM RUST OF WHEAT AND ITS MANAGEMENT
MANAGEMENT:
 Eradication of self sown wheat plants and weed hosts.
 Eradication of alternate host: Elimination of the alternate host
disrupts the life cycle of the pathogen and thus causes a reduction of
initial inoculum, along with a decrease in pathogen genetic
variability (Roelfs ,1982).
 Cultural management: Cultural practices like judicious application
of nitrogen fertilizers, mixed cropping, choice of well drained upland
planting site , adjustment of sowing time etc.

19. LOOSE SMUT OF WHEAT

20. DISEASE CYCLE OF LOOSE SMUT OF WHEAT AND ITS
MANAGEMENT
CYCLE:
 The fungus is carried over in the seed as dormant mycelium.
 When the planted seed germinates the mycelium becomes active
and grows along with the plant and when the panicle is produced the
mycelium reaches the ovaries and transforms the ovaries into a mass
of black smut spores.
 Secondary spread occurs through wind borne smut spores.
 The sporidia infect the healthy flowers. The mycelium enters the
ovary and remains in the seed as dormant mycelium.
MANAGEMENT:
 As the secondary inoculum spread occurs through wind and a fresh
flower is required for landing of the smut spores, for sporidia to
cause infection , thereby coincidence of flowering of healthy plant
and with spore dissemination can be prevented by adjustment of
time of planting and maintenance of proper spacing.
 Seed treatment

21. CLUB ROOT OF CABBAGE

22. DISEASE CYCLE OF CLUB ROOT OF CABBAGE AND ITS MANAGEMENT
CYCLE:
 Entrance through root hairs and injured roots.
 Roots becomes abnormally enlarged because of the plasmodium
inside the root cells.
 The fungus transforms into a mass of spores that are released into
the soil upon decay of the host tissue.
 Spores of the fungus are spread in infested soil or water.
 The organism can remain viable in soil for a period of 7-10 years.
MANAGEMENT:
 Provide and maintain well drained soil.
 In fields where the disease has occurred, rotate cruciferous crops
with unrelated crops for a period of 7-10 years. Each time cabbage
is planted in the rotation, hydrated lime should be applied.
 The most important step in control is to locate the plant bed in an
area where diseased cabbage has not been grown and where
infested soil cannot wash over it.

23. CONCLUSION
Plant disease cycles represent pathogen biology as
series of interconnected stages of development of
disease and expression of symptom in plant.
The disease cycle for all pathogens is essentially the same.
Effective management strategies break the disease cycle.
An understanding of the disease cycle will help to
implement effective management strategies.

24. THANK YOU