BASIC PRINCIPLES OF PLANT PATHOLOGY AND PLANT DISEASE MANAGEMENT
Plant Pathology or
phytopathology is a
branch of agricultural,
botanical or biological science which
deals with cause, etiology,
losses and control
of plant diseases. Disease is
a malfunctioning process
caused by continuous
irritation. A plant is
said to be
diseased when one
or more of
its functions are
interfered by pathogen. The pathogen
is any agent
that causes pathos
(ailment / suffering) or damage. It include
all living organisms
associated with causation
of diseases, viruses as well
as abiotic agents
such as adverse
atmospheric or soil conditions. However, the term
is generally used
to denote living
organisms (fungi, bacteria, mycoplasma like organisms,
nematodes etc.) and
viruses but not
abiotic causes. Pathogenicity is the ability of a
pathogen to cause disease and pathogenesis is the chain of events that leads to the development of disease in plants.
Recognition between host and pathogen
It is not much clear how pathogens recognize their hosts and vice-versa. It is
assumed that when a pathogen comes in contact with a host cell, an early event takes place that triggers a fairly rapid response in each organism that either allows or impedes further growth of the pathogen and development of disease. These may include specific host signal compounds or structures, or specific pathogen elicitor molecules, and either of them may induce specific actions or formation of specific products by the other organism which decides whether reaction will be compatible or incompatible.
Concept of Infection
After landing on the host or having come in contact with the living host surface through dissemination by seed, soil or air, the pathogen generally initiate the process of infection. The success of this process depends on many factors. The host should be susceptible, the virulent pathogen, and have favourable environmental conditions for pathogen. Most fungal pathogens first grow on host surface before penetration to achieve proper numerical and chemical strength. In other fungi, spores germinate and either by the germ tube by itself cause penetration directly or indirectly or it first
produces an appressorium from which infection thread develops and penetrate the host. Indirect penetration takes place through wounds and natural openings. In direct penetration into the host the pathogen exerts its own efforts to break the host barriers and directly enters through the cuticle or epidermis without seeking the help of wounds and natural openings. Direct penetration by pathogens is through use of mechanical force (fungi and nematodes) or by chemical action or both. Pathogens are known to produce enzymes to degrade cuticle, epidermis and cell walls to reach to protoplasm. These substances of fungus or bacterium help in tissue disintegration, modification of protoplasm for use and other biochemical activities associated with pathogenesis.The viruses are passive in transmission and they reach the interior of host cells only with activity of organs of their vector or by some other mechanical means. Bacteria enter into host cells through wounds or natural openings.
Infection
Infection is said to occur when hyphae developing from infection tube or
bacterial cells that have entered are able to establish biological relationship with host cells, absorb nutrients and with further development, cause tissue disintegration, produce toxins and other harmful substances.
In viral infection the virus comes in contact with host protoplasm. Their
nucleic acid induces the host nucleic acid to form more virus nucleic acid. This malfunction of the host nucleus results in pathogenesis. Bacteria and fungi dissolve cell walls by their enzymes after entry into host and absorb nutrients or fungi may produce special organs (haustoria) which penetrate the cell walls and lie in the protoplasm, absorption of nutrients taking place through osmosis. Chemical interactions occurring during these processes lead to disease development. The pathogens colonize host tissues and then exit from host to spread to new hosts.
Symptomatology
The pathogens induce reactions in the body of their host. As a result of these
reactions certain abnormalities appear on the plant. In addition the pathogen itself may become visible on the host surface giving it abnormal appearance. The abnormalities, sign or evidence of disorder, are known as symptoms of the disease.
A. Signs
1. Downy mildew:- Sporangiophore and sporangia of the fungus appear as downy growth on the lower surface of leaves. They appear as white, grey, brownish or purplish growth on the host surface e.g., Downy mildew of Pearl millet.
2. Powdery mildew: - Appearance of white to dirty white powdery mass on plant surface comprising conidiophores, conidia or mycelium of the fungus e.g., Powdery mildew of Pea.
3. Rust: - A disease giving a rusty appearance to a plant and caused by one of the members of uredinales. It relatively appears as small pustules of spores usually breaking through the host epidermis. The pustules may be red, black or yellow e.g., Rusts of Wheat.
4. Smut: - A sooty or black or charcoal like powdery mass produced by members of ustilaginales which can be seen on affected plant parts and usually symptoms appear on floral parts e.g., Loose smut of Wheat.
5. White blister: - Numerous white blisters like pustules which break open the host epidermis and expose powdery mass of spores. They are similar to the rust.e.g. White rust or blister of Rapeseed- Mustard.
6. Bunt: - A disease in which the grain contents are replaced by odorous smut spores. Normally belonging to fungi of family Tilletiaceae e.g., Bunt of wheat.
7. Mould: - A sooty or black coating on foliage or on fruits formed by dark hyphae of fungi. Sometimes it is caused by green hyphae of fungi-as green coating, and then it is known as green mould e.g., Green mould of Citrus.
8. Blotch: - It refers to the superficial discolouration of the leaves or fruits along with necrosis e. g., Purple blotch of Onion.
9. Scab: - It refers to ulcer like lesions on fruits or roughened or crust like symptoms on tubers and leaves etc. It is due to over growth of cortical and epidermal cells e.g., Apple scab.
10. Exudation: - In certain diseases a fluid is exuded from the infected tissues and phenomenon is known as exudation. A continuous flow of liquid from the lesion is known as bleeding (usually do not contain pathogen cell). When exudates mixed with pathogen as in case of bacterial diseases, it is called as ooze. If the gummy ooze from the lesions dries up into a hard / semi hard gummy masses it is called as gummosis.
11. Sclerotia: - Sclerotia are a compact mass of dormant fungal mycelium. Sclerotia are most often black or they may be buff or dark brown in colour.
12. Ergot: - Appearance of creamy droplets of a sticky liquid exuding from young florets of infected heads which are soon replaced by hard sclerotia of the fungus e.g., Ergot of Pearl millet.
B. Symptoms due to some effect or change in the host plant
1. Discolouration:
A. Avoidance of pathogen: Avoiding disease by planting at times when, or in areas where, inoculum is ineffective due to environmental conditions, or is rare or absent. Many diseases can be managed by proper selection of field, choice of sowing time, selection of cultivars, seed and planting stocks, and modification cultural practices. The aim of these measures is to enable the host to avoid contact with the pathogen or the susceptible stage of the plant and favourable conditions should not coincide. The main principles under this group are selection of geographical area, selection of field, choice of sowing time, selection of planting
materials, disease escaping varieties and modification of cultural practices etc.
C. Eradication of pathogen: Reducing, inactivating, eliminating or destroying
inoculum at source, either from a region or from an individual plant in which it is already established. This is attempted through the methods such as biological control, crop rotation and sanitation etc.
D. Protection: The inoculum of many fast spreading infectious diseases is brought by wind from neihbouring fields or any other distant place of survival. Protective measures are necessary to destroy or inactivate such inoculum. It is possible by creating a chemical toxic barrier between the plant surface and the invading pathogen. Methods employed to achieve such results are chemical sprays, dusts, modification of environment and host nutrition etc.
F. Therapy: Reducing severity of a disease in an infected individual through curative procedures such as management of physical environment including cultural control, management of associated microbiota which includes antagonism, management with chemicals and management with therapy, radiation and meristem culture.
Basis of Disease Management Principles
• Management of the disease triangle
– Disease - Interaction of host, pathogen and environment
– None of them alone can operate to cause a disease
– This constitute the disease triangle
– Principles of management should tackle all the three
• Management of pathogen-reduction, eradication and prevention of inoculum through quarantine.
• Management of host- Practices directed to improve plant vigour, induced resistance through nutrition, induction of genetic resistance and providing protection through chemical and biological means
• Management of environment-involves water, soil and crop management
A. Avoidance of the Pathogen
• Choice of geographical area
– Ergot of bajra (More severe in wet areas)
– Bean anthracnose and bacterial blight (more severe in wet areas).
– Potato seed tuber production (in cooler regions at higher altitude for virus free tubers)
– Karnal bunt of wheat (more severe in wet areas).
• Selection of the field
– Many soil borne diseases can be avoided by proper selection of the field (This can be ascertained on the basis of previous history of field and nature of the pathogen)
• Root-rots, wilts, stem rots, red rot
• Choice of sowing time
Recognition between host and pathogen
It is not much clear how pathogens recognize their hosts and vice-versa. It is
assumed that when a pathogen comes in contact with a host cell, an early event takes place that triggers a fairly rapid response in each organism that either allows or impedes further growth of the pathogen and development of disease. These may include specific host signal compounds or structures, or specific pathogen elicitor molecules, and either of them may induce specific actions or formation of specific products by the other organism which decides whether reaction will be compatible or incompatible.
Concept of Infection
After landing on the host or having come in contact with the living host surface through dissemination by seed, soil or air, the pathogen generally initiate the process of infection. The success of this process depends on many factors. The host should be susceptible, the virulent pathogen, and have favourable environmental conditions for pathogen. Most fungal pathogens first grow on host surface before penetration to achieve proper numerical and chemical strength. In other fungi, spores germinate and either by the germ tube by itself cause penetration directly or indirectly or it first
produces an appressorium from which infection thread develops and penetrate the host. Indirect penetration takes place through wounds and natural openings. In direct penetration into the host the pathogen exerts its own efforts to break the host barriers and directly enters through the cuticle or epidermis without seeking the help of wounds and natural openings. Direct penetration by pathogens is through use of mechanical force (fungi and nematodes) or by chemical action or both. Pathogens are known to produce enzymes to degrade cuticle, epidermis and cell walls to reach to protoplasm. These substances of fungus or bacterium help in tissue disintegration, modification of protoplasm for use and other biochemical activities associated with pathogenesis.The viruses are passive in transmission and they reach the interior of host cells only with activity of organs of their vector or by some other mechanical means. Bacteria enter into host cells through wounds or natural openings.
Infection
Infection is said to occur when hyphae developing from infection tube or
bacterial cells that have entered are able to establish biological relationship with host cells, absorb nutrients and with further development, cause tissue disintegration, produce toxins and other harmful substances.
In viral infection the virus comes in contact with host protoplasm. Their
nucleic acid induces the host nucleic acid to form more virus nucleic acid. This malfunction of the host nucleus results in pathogenesis. Bacteria and fungi dissolve cell walls by their enzymes after entry into host and absorb nutrients or fungi may produce special organs (haustoria) which penetrate the cell walls and lie in the protoplasm, absorption of nutrients taking place through osmosis. Chemical interactions occurring during these processes lead to disease development. The pathogens colonize host tissues and then exit from host to spread to new hosts.
Symptomatology
The pathogens induce reactions in the body of their host. As a result of these
reactions certain abnormalities appear on the plant. In addition the pathogen itself may become visible on the host surface giving it abnormal appearance. The abnormalities, sign or evidence of disorder, are known as symptoms of the disease.
A. Signs
1. Downy mildew:- Sporangiophore and sporangia of the fungus appear as downy growth on the lower surface of leaves. They appear as white, grey, brownish or purplish growth on the host surface e.g., Downy mildew of Pearl millet.
2. Powdery mildew: - Appearance of white to dirty white powdery mass on plant surface comprising conidiophores, conidia or mycelium of the fungus e.g., Powdery mildew of Pea.
3. Rust: - A disease giving a rusty appearance to a plant and caused by one of the members of uredinales. It relatively appears as small pustules of spores usually breaking through the host epidermis. The pustules may be red, black or yellow e.g., Rusts of Wheat.
4. Smut: - A sooty or black or charcoal like powdery mass produced by members of ustilaginales which can be seen on affected plant parts and usually symptoms appear on floral parts e.g., Loose smut of Wheat.
5. White blister: - Numerous white blisters like pustules which break open the host epidermis and expose powdery mass of spores. They are similar to the rust.e.g. White rust or blister of Rapeseed- Mustard.
6. Bunt: - A disease in which the grain contents are replaced by odorous smut spores. Normally belonging to fungi of family Tilletiaceae e.g., Bunt of wheat.
7. Mould: - A sooty or black coating on foliage or on fruits formed by dark hyphae of fungi. Sometimes it is caused by green hyphae of fungi-as green coating, and then it is known as green mould e.g., Green mould of Citrus.
8. Blotch: - It refers to the superficial discolouration of the leaves or fruits along with necrosis e. g., Purple blotch of Onion.
9. Scab: - It refers to ulcer like lesions on fruits or roughened or crust like symptoms on tubers and leaves etc. It is due to over growth of cortical and epidermal cells e.g., Apple scab.
10. Exudation: - In certain diseases a fluid is exuded from the infected tissues and phenomenon is known as exudation. A continuous flow of liquid from the lesion is known as bleeding (usually do not contain pathogen cell). When exudates mixed with pathogen as in case of bacterial diseases, it is called as ooze. If the gummy ooze from the lesions dries up into a hard / semi hard gummy masses it is called as gummosis.
11. Sclerotia: - Sclerotia are a compact mass of dormant fungal mycelium. Sclerotia are most often black or they may be buff or dark brown in colour.
12. Ergot: - Appearance of creamy droplets of a sticky liquid exuding from young florets of infected heads which are soon replaced by hard sclerotia of the fungus e.g., Ergot of Pearl millet.
B. Symptoms due to some effect or change in the host plant
1. Discolouration:
a. Etiolation:
Yellowing due to lack of light or prolonged exposure to darkness b. Chlorosis:
Appearance of yellow
colour in place
of green colour
due to low temperature, iron deficiency,
excess of lime or infection by viruses, fungi and bacteria.
c. Chromosis:
Change of green
colour to red,
purple or orange
is called chromosis.
d. Mosaic: Uneven development of chlorophyll producing
light green patches with dark green areas.
e. Albinism:
Change of green colour to white
2.Over growth or Hypertrophy:
2.Over growth or Hypertrophy:
a. Gall:
Abnormal development of
infected plant parts may
be due to hypertrophy or
hyperplasia. It may
be more or
less globosely, elongated
or irregular. e.g. Crown gall, Club
root of Crucifers.
b.
Witches broom: Numerous
slender branches arise
from a limited
region in close clusters just like a broom.
e.g. Witches broom of Potato.
c. Rugosity: Veins become sunken and inter veinal portion
is elevated.
d. Rossetting: Crowded condition of foliage due to lack
of internodal elongation.
e. Curling:
It refers to
the abnormal bending
or rolling or
folding of plant organs particularly in leaf due to
localized out growth of host tissues.
f. Epinasty:
Downward curvature of
leaf due to
more growth at
some portion.
g. Enation:
Overgrowth or tumor like
structure appears on surface
of leaf along with veins.
h. Phyllody: Floral parts develop into leaf like
structures.
3. Atrophy or Dwarfing or Stunting:
3. Atrophy or Dwarfing or Stunting:
It is abnormal development of
most of the plant parts causing reduction in plant height, leaf size and other
organs.
4. Necrotic symptoms
4. Necrotic symptoms
a.
Blight: Rapid killing or
sudden death of
plant or plant
parts. It gives
burnt appearance.
b. Blotch: Appearance of large, irregular lesions on
leaves, shoots and stems.
c. Canker: Necrotic
lesions often sunken
in the cortical
tissues of stem, leaves or twigs.
d. Anthracnose: Appearance of black sunken lesions on leaf, stem and fruit and pathogen produce fruiting bodies i.e. acervuli on infected tissues.
d. Anthracnose: Appearance of black sunken lesions on leaf, stem and fruit and pathogen produce fruiting bodies i.e. acervuli on infected tissues.
e. Die back:
Dying of
plant organs especially
the branches from
top to downwards.
f. Damping off: Death of the seedlings near the soil level
as a result of which the seedling topples down on the
ground.
g. Scald: Death of plant organs due to effect of high
temperature.
h. Rot: The affected tissue die, decompose and turn
brown. It takes place due to the production of cell wall
degrading enzymes by the pathogen.
i. Lesion: It refers to the distinct and localized spot
on the host tissues.
j. Spots: Usually defined as circular or oval shape with
central necrotic areas surrounded by variously coloured
zones. Some times they are restricted by veins.
k. Shot hole:
Circular hole in
leaves resulting from
the drooping out or detaching of the central necrotic
areas.
l. Streak or stripe: development of
minute linear lesions
known as streak. Enlargement of
streaks into variable
length and breadth
are known as stripes.
m. Wilt: The leaves and other succulent parts loose their
turgidity and droop.
n. Hydrosis: A
water soaked translucent
conditions of the
tissue due to
cell sap passing into intercellular
spaces.
o. Scorch: Browning of leaf margins
resulting from death of the tissues
Survival of plant pathogens :
Survival of plant pathogens :
In
absence of cultivated
host, animate pathogens
must find some
alternate
source of their survival otherwise infection chain will remain incomplete. The same holds true for viral diseases. The pathogens of perennial cultivated plants do not face problem of survival because the host is available for several years. Pathogens may survive on cultivated host, alternate hosts and collateral hosts. In absence of cultivated host, the facultative parasites are capable of surviving as saprophytes. Soil and plant debris serve as media for this saprophytic survival. Antagonism by other soil microflora reduces their ability to continue saprophytic activity unless they have strong competitive saprophytic ability. Fungi can survive through resting or dormant structures. The dormant structures of survival of fungi may be conidia, chlamydospores, oospores, perithecia, cleistothecia, sclerotia etc. When facultative saprophytes are unable to continue as saprophytes in plant debris or in soil they produce dormant spores.
Dispersal of plant pathogens
Dispersal of infectious plant pathogens can be grouped in two. The direct
(active or autonomous dispersal) and indirect (passive dispersal). The knowledge of these methods of dispersal is essential for effective control of plant diseases because possibilities of preventing dispersal and there by breaking the infection chain exist. Autonomous dispersal of bacteria, fungi, and viruses is accomplished through the agency of soil, seed and plant organs during normal agronomic operations. There is no major role of external agencies like animals, wind and water etc in this type of dispersal. Passive dispersal of plant pathogens is accomplished through the agency of members of animal kingdom such as man, insects, nematodes, animals, birds etc. air and water.
Effect of environment on disease development
The disease results from the interaction of a pathogen with its host but the intensity and extent of this interaction is markedly affected by the environmental factors. Although these factors are not the causal agents of infectious diseases yet they are the final determinants of almost all the events that constitute the infection chain. The role of environments in pathogenesis is as important as susceptibility of host and pathogenecity of the causal agent. The first step in infection chain is survival of pathogen. Adverse environment (physical, chemical, biotic) can limit survival ability and reduce the density and capacity of inoculum. The transport or dispersal of inoculum is also dependent on environment in speed and distance.
Germinability of spores, and the number and flight range of insect vectors are directly influenced by prevailing weather. At the time of penetration, the structural defense barriers of the host, stability and germination of spores on the host surface and their penetration are influenced by meteorological conditions. The factors such as light, temperature and humidity on host surface also definitely determine the exit of pathogen, its sporulation and amount of secondary inoculum produced for dispersal. Thus, it is obvious that inspite of the pathogen is being virulent and host being susceptible, disease may not develop in a population unless environmental conditions are favourable for it.
Principles of disease management
source of their survival otherwise infection chain will remain incomplete. The same holds true for viral diseases. The pathogens of perennial cultivated plants do not face problem of survival because the host is available for several years. Pathogens may survive on cultivated host, alternate hosts and collateral hosts. In absence of cultivated host, the facultative parasites are capable of surviving as saprophytes. Soil and plant debris serve as media for this saprophytic survival. Antagonism by other soil microflora reduces their ability to continue saprophytic activity unless they have strong competitive saprophytic ability. Fungi can survive through resting or dormant structures. The dormant structures of survival of fungi may be conidia, chlamydospores, oospores, perithecia, cleistothecia, sclerotia etc. When facultative saprophytes are unable to continue as saprophytes in plant debris or in soil they produce dormant spores.
Dispersal of plant pathogens
Dispersal of infectious plant pathogens can be grouped in two. The direct
(active or autonomous dispersal) and indirect (passive dispersal). The knowledge of these methods of dispersal is essential for effective control of plant diseases because possibilities of preventing dispersal and there by breaking the infection chain exist. Autonomous dispersal of bacteria, fungi, and viruses is accomplished through the agency of soil, seed and plant organs during normal agronomic operations. There is no major role of external agencies like animals, wind and water etc in this type of dispersal. Passive dispersal of plant pathogens is accomplished through the agency of members of animal kingdom such as man, insects, nematodes, animals, birds etc. air and water.
Effect of environment on disease development
The disease results from the interaction of a pathogen with its host but the intensity and extent of this interaction is markedly affected by the environmental factors. Although these factors are not the causal agents of infectious diseases yet they are the final determinants of almost all the events that constitute the infection chain. The role of environments in pathogenesis is as important as susceptibility of host and pathogenecity of the causal agent. The first step in infection chain is survival of pathogen. Adverse environment (physical, chemical, biotic) can limit survival ability and reduce the density and capacity of inoculum. The transport or dispersal of inoculum is also dependent on environment in speed and distance.
Germinability of spores, and the number and flight range of insect vectors are directly influenced by prevailing weather. At the time of penetration, the structural defense barriers of the host, stability and germination of spores on the host surface and their penetration are influenced by meteorological conditions. The factors such as light, temperature and humidity on host surface also definitely determine the exit of pathogen, its sporulation and amount of secondary inoculum produced for dispersal. Thus, it is obvious that inspite of the pathogen is being virulent and host being susceptible, disease may not develop in a population unless environmental conditions are favourable for it.
Principles of disease management
The methods of disease control have been classified in to six groups.
A. Avoidance of pathogen: Avoiding disease by planting at times when, or in areas where, inoculum is ineffective due to environmental conditions, or is rare or absent. Many diseases can be managed by proper selection of field, choice of sowing time, selection of cultivars, seed and planting stocks, and modification cultural practices. The aim of these measures is to enable the host to avoid contact with the pathogen or the susceptible stage of the plant and favourable conditions should not coincide. The main principles under this group are selection of geographical area, selection of field, choice of sowing time, selection of planting
materials, disease escaping varieties and modification of cultural practices etc.
B. Exclusion of inoculum: Preventing
the inoculum from entering or establishing in the field or area where it does not exist. Seed certification, crop inspection,
growing crops in regions unfavourable for pathogens and quarantine measures are some of
the means of preventing the spread of the pathogen.
C. Eradication of pathogen: Reducing, inactivating, eliminating or destroying
inoculum at source, either from a region or from an individual plant in which it is already established. This is attempted through the methods such as biological control, crop rotation and sanitation etc.
D. Protection: The inoculum of many fast spreading infectious diseases is brought by wind from neihbouring fields or any other distant place of survival. Protective measures are necessary to destroy or inactivate such inoculum. It is possible by creating a chemical toxic barrier between the plant surface and the invading pathogen. Methods employed to achieve such results are chemical sprays, dusts, modification of environment and host nutrition etc.
E.
Disease resistance:
Preventing infection or
reducing the effect
of infection by managing the host through improvement of resistance in it by genetic
manipulation or by
chemotherapy. In any
crop, resistance against
a specific disease
can be developed by selection
or hybridization. This
type of resistance
is genetic. Biochemical resistance of
non-genetic nature can
be developed in
plants by chemotherapy or
modification of nutrition.
This type of
resistance is induced
and temporary, lasting until the chemical or nutrient is effective in the plant.
F. Therapy: Reducing severity of a disease in an infected individual through curative procedures such as management of physical environment including cultural control, management of associated microbiota which includes antagonism, management with chemicals and management with therapy, radiation and meristem culture.
Basis of Disease Management Principles
• Management of the disease triangle
– Disease - Interaction of host, pathogen and environment
– None of them alone can operate to cause a disease
– This constitute the disease triangle
– Principles of management should tackle all the three
• Management of pathogen-reduction, eradication and prevention of inoculum through quarantine.
• Management of host- Practices directed to improve plant vigour, induced resistance through nutrition, induction of genetic resistance and providing protection through chemical and biological means
• Management of environment-involves water, soil and crop management
A. Avoidance of the Pathogen
• Choice of geographical area
– Ergot of bajra (More severe in wet areas)
– Bean anthracnose and bacterial blight (more severe in wet areas).
– Potato seed tuber production (in cooler regions at higher altitude for virus free tubers)
– Karnal bunt of wheat (more severe in wet areas).
• Selection of the field
– Many soil borne diseases can be avoided by proper selection of the field (This can be ascertained on the basis of previous history of field and nature of the pathogen)
• Root-rots, wilts, stem rots, red rot
• Choice of sowing time
– Many
diseases are severe
when susceptible stage
of plant coincide with pathogen under
favourable conditions
• By altering sowing time avoid the
• By altering sowing time avoid the
– Sowing of gram
in November suffers
less than October
sown crop. – Early sown crop of mustard suffers less from white compared to
late sown crop.
• Disease escaping varieties
• Disease escaping varieties
– Certain
varieties escape damage
by disease because
of their growth factors.
• Early maturing varieties of pea (Matures in January) usually escape damage from powdery mildew and rust.
• Selection of seed and planting stock
• Early maturing varieties of pea (Matures in January) usually escape damage from powdery mildew and rust.
• Selection of seed and planting stock
– Many
diseases are introduced
by these and
can be easily controlled by proper selection of the
planting material
• Various smuts, red rot of sugarcane, black scurf of potato
• Modification of cultural practices
• Various smuts, red rot of sugarcane, black scurf of potato
• Modification of cultural practices
– Plant
to plant distance,
time and amount
of irrigation, quantity
and quality of fertilizer, time
and method of planting, mixed cropping, of sowing.
• Necessary
modifications in these
practices can help
in
managing the disease.
B. Exclusion of Inoculum
Objective of exclusion is to prevent spread of the disease when avoidance has failed or is not feasible
• Seed treatment: Any planting material can be given heat, gas or chemical treatment to exclude the pathogen present in or on them.
• Inspection and certification: Crops grown exclusively for seed-Periodical inspection for presence of diseases and removal of diseased plants. By this Inter and Intra-regional spread of seed borne diseases can be prevented.
• Exclusion of insect vectors: Many diseases spread through insects which transfer the inoculum from one region to another region depending upon their flight range-Therefore exclusion of insect vectors is essential.
• Exclusion through plant quarantine - To prevent the import and spread of plant pathogens into areas from which they are absent, national and state laws regulate the conditions under which certain crops susceptible to such pathogens may be grown and distributed between states and countries.
Directorate of Plant Protection, Quarantine and Storage (DPPQ&S, Ministry of Agriculture) work through its national Network of Plant Quarantine and Fumigation Stations
C. Eradication of the pathogen
• Pathogen can enter an area or crop in spite of avoidance and exclusion or inoculum may already present in the field. So eradication of pathogen inoculum can be attempted through biological, cultural, physical or chemical methods.
• Biological control of plant pathogens
– Aims at eradication and control of pathogens through activity of other
microorganisms. Such procedure enhance activity of m.o. in soil or at
infection site and effect may be biocidal or biostatic
• Introduction of bioagents (fungal and bacterial antagonists)
• Soil amendments with organic matters (enhances microbial
activity)
• Crop rotation
– By continuous growing the same crop in the same field for many years
enhance soil borne pathogens
• Soil borne diseases particularly those pathogens which can
survive in the soil for a limited period, crop rotation helps in
eradicating the inoculum of such pathogens
• Red rot of sugarcane (one year crop rotation)
• Wilt, root rot (three years crop rotation)
• Removal and destruction of diseased plants or plant organs
– Eradication of alternate or collateral host– Field sanitation (destruction of diseased crop debris, burying the
debris deep in soil) for facultative parasite and saprophytes
• Powdery mildew of wheat, barley and peas
• Downy mildew of bajra, mustard, maize, red rot of sugarcane
• Heat and chemical treatment of diseased plants
– It is employed to destroy resting structure or exposed growth of the
pathogen on the host
• Wheat seed treatment with Vitavax for loose smut control
• Moist hot air treatment at 54ºC for 2 h for the control of GSD
and RSD in sugarcane.
• Soil treatment
– Aim is to inactivate or eradicate the pathogen present in the soil
• Chemical treatment for nurseries and small fields using
fungicides namely Captan, Bavistin, Kitazine granules etc.
(Pythium, Rhizoctonia and Sclerotium)
• Soil fumigation by formaldehyde, chloropicrin or vapam for soil
borne pathogen
• Steam is also used in some countries in polyhouses
• Flooding of the field to create anaerobic condition or low oxygen
condition (Pathogen like Fusarium can be controlled)
• Soil solarization in summer months (manages many soil borne
pathogens)
D. Protective Measures
Protective measures are necessary to destroy or inactivate the inoculum
which can not be prevented by other methods
– Chemical treatment: Aim of most chemical sprays is to form a
protective layer on host surface to prevent or to kill the pathogen
growth (Protectants)
– Some of chemicals, eradicate the already established pathogens from
the host (Eradicants)
• Chemical control of insect vector
– Control of insect vectors by insecticides will help in minimising the viral and
other diseases
• Modification of the environment
– Improved aeration reduces humidity (Recommended for control of
white rust in Rapeseed & mustard, Downy mildew of grapes)
– Mixed cultivation of cotton and moth reduces the incidence of root rot
(Less disease due to low temperature and high moisture by lush
growth of moth)
– Post harvest rot of fruits and vegetables (storing in cool and dry rooms
reduce rot by fungi and bacteria)
• Modification of host nutrition
– Many leaf diseases are favoured by high nitrogen doses (Wheat rust,
Alternaria blight of mustard, red rot of sugarcane)
– Potassium application usually decrease disease (Rice blast,
Helminthosporium blight in various crops
– High calcium increases resistance to wilt (strengthening of pectic
substances in cell wall thereby interfere in activity of pectic enzymes of
the pathogen)
E. Development of Resistance in Plants
• Through selection or hybridization (Vertical & Horizontal resistance)
• Through induced/systemic acquired resistance by chemicals or biological means (Plant defense activators – salicylic acid is a common derivative of acetyl salicylic acid (Aspirin), dichloroisonicotinic acid. They induce resistance in several host-pathogen combinations.
F. Therapy of Diseased Plants
• Reducing severity of the disease in an infected individual
– Chemotherapy
– Heat therapy
– Tree surgery
managing the disease.
B. Exclusion of Inoculum
Objective of exclusion is to prevent spread of the disease when avoidance has failed or is not feasible
• Seed treatment: Any planting material can be given heat, gas or chemical treatment to exclude the pathogen present in or on them.
• Inspection and certification: Crops grown exclusively for seed-Periodical inspection for presence of diseases and removal of diseased plants. By this Inter and Intra-regional spread of seed borne diseases can be prevented.
• Exclusion of insect vectors: Many diseases spread through insects which transfer the inoculum from one region to another region depending upon their flight range-Therefore exclusion of insect vectors is essential.
• Exclusion through plant quarantine - To prevent the import and spread of plant pathogens into areas from which they are absent, national and state laws regulate the conditions under which certain crops susceptible to such pathogens may be grown and distributed between states and countries.
Directorate of Plant Protection, Quarantine and Storage (DPPQ&S, Ministry of Agriculture) work through its national Network of Plant Quarantine and Fumigation Stations
C. Eradication of the pathogen
• Pathogen can enter an area or crop in spite of avoidance and exclusion or inoculum may already present in the field. So eradication of pathogen inoculum can be attempted through biological, cultural, physical or chemical methods.
• Biological control of plant pathogens
– Aims at eradication and control of pathogens through activity of other
microorganisms. Such procedure enhance activity of m.o. in soil or at
infection site and effect may be biocidal or biostatic
• Introduction of bioagents (fungal and bacterial antagonists)
• Soil amendments with organic matters (enhances microbial
activity)
• Crop rotation
– By continuous growing the same crop in the same field for many years
enhance soil borne pathogens
• Soil borne diseases particularly those pathogens which can
survive in the soil for a limited period, crop rotation helps in
eradicating the inoculum of such pathogens
• Red rot of sugarcane (one year crop rotation)
• Wilt, root rot (three years crop rotation)
• Removal and destruction of diseased plants or plant organs
– Eradication of alternate or collateral host– Field sanitation (destruction of diseased crop debris, burying the
debris deep in soil) for facultative parasite and saprophytes
• Powdery mildew of wheat, barley and peas
• Downy mildew of bajra, mustard, maize, red rot of sugarcane
• Heat and chemical treatment of diseased plants
– It is employed to destroy resting structure or exposed growth of the
pathogen on the host
• Wheat seed treatment with Vitavax for loose smut control
• Moist hot air treatment at 54ºC for 2 h for the control of GSD
and RSD in sugarcane.
• Soil treatment
– Aim is to inactivate or eradicate the pathogen present in the soil
• Chemical treatment for nurseries and small fields using
fungicides namely Captan, Bavistin, Kitazine granules etc.
(Pythium, Rhizoctonia and Sclerotium)
• Soil fumigation by formaldehyde, chloropicrin or vapam for soil
borne pathogen
• Steam is also used in some countries in polyhouses
• Flooding of the field to create anaerobic condition or low oxygen
condition (Pathogen like Fusarium can be controlled)
• Soil solarization in summer months (manages many soil borne
pathogens)
D. Protective Measures
Protective measures are necessary to destroy or inactivate the inoculum
which can not be prevented by other methods
– Chemical treatment: Aim of most chemical sprays is to form a
protective layer on host surface to prevent or to kill the pathogen
growth (Protectants)
– Some of chemicals, eradicate the already established pathogens from
the host (Eradicants)
• Chemical control of insect vector
– Control of insect vectors by insecticides will help in minimising the viral and
other diseases
• Modification of the environment
– Improved aeration reduces humidity (Recommended for control of
white rust in Rapeseed & mustard, Downy mildew of grapes)
– Mixed cultivation of cotton and moth reduces the incidence of root rot
(Less disease due to low temperature and high moisture by lush
growth of moth)
– Post harvest rot of fruits and vegetables (storing in cool and dry rooms
reduce rot by fungi and bacteria)
• Modification of host nutrition
– Many leaf diseases are favoured by high nitrogen doses (Wheat rust,
Alternaria blight of mustard, red rot of sugarcane)
– Potassium application usually decrease disease (Rice blast,
Helminthosporium blight in various crops
– High calcium increases resistance to wilt (strengthening of pectic
substances in cell wall thereby interfere in activity of pectic enzymes of
the pathogen)
E. Development of Resistance in Plants
• Through selection or hybridization (Vertical & Horizontal resistance)
• Through induced/systemic acquired resistance by chemicals or biological means (Plant defense activators – salicylic acid is a common derivative of acetyl salicylic acid (Aspirin), dichloroisonicotinic acid. They induce resistance in several host-pathogen combinations.
F. Therapy of Diseased Plants
• Reducing severity of the disease in an infected individual
– Chemotherapy
– Heat therapy
– Tree surgery
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