PAT 219. Applied
Plant Pathology (2+1)
Objectives
The subject
covers the basic aspects of plant disease management through physical, chemical
and biological methods devising for effective management techniques to reduce
the losses.
Unit – 1 Principles of Plant disease management
History
of disease management – definition for Plant diseases – Causes of Plant
diseases – Classification of Plant diseases – Principles of Plant disease
management – Prophylaxis and Immunization – Prophylaxis: Avoidance, Exclusion,
Eradication and direct protection.
History of Plant disease
management
1000 B.C. – Homer, the
Greek poet made a mention of sulphur with pest controlling properties.
1761 – Sculthess first
suggested the use of copper sulphate on wheat seed against stinking smut.
1807 -
Copper sulphate was recommended for wheat seed treatment against bunt by
Prevost who for the first time established the fungitoxic value of the
compound.
1821- Robertson of
England stated that Sulphur is effective against powdery mildew of peach.
1882 - The modern era of
chemical control of plant diseases started with the discovery of Bordeaux
mixture during the epidemic of grape downy mildew in France during 1875. The
mixture of copper sulphate and slaked lime had been sprinkled on the grapevines
to deter the pilferage.
1887 - Mason of France
introduced Burgundy mixture using copper sulphate and sodium carbonate in place
of lime.
1887 – Jensen developed
hot water treatment for control of wheat smut.
1889 – Weed of the USA
for the first time used fungicides in combination with insecticides.
1891 – N.A.Cobb devised first scale to
measure plant disease intensity.
1910- The first
description of a germination test for evaluating fungicides was done by Donald
Reddick and E.Wallace.
1929 –Cross protection or
Pre-immunization technique was developed by H.H.Mckinney
1934 – W.H.Tisdale and I.
Williams reported fungitoxicity of dithiocarbamates.
1940 – Burlingham and
reddish proposed the “Zone of inhibition” technique for fungicidal bioassays.
1952 – Kittleson
introduced captan as a fungicide. (Kittleson’s killer)
1966 - Systemic fungicides
introduced by Van Schleming and Marshal Kulka. (oxathiins, Carboxin)
1968 – Delp and Klopping
reported systemic fungicidal properties of benomyl.
1978 – Fosetyl –Al, a
metal based systemic fungicide effective against phycomycetes with pronounced
basipetal translocation was developed under code number LS-74-783.
1981 – Fungicide
Resistance Action Committee (FRAC) was founded.
1996 – First Strobilurins
fungicide launched, which was isolated from wood rotting mushroom fungi (Strobilurus tenacellus; Basidiomycetes
fungus).
1931 - Sanford and
Broadfort were the first to use the terms Biological control and suppressive
effect in Plant pathology.
1932 – The first
suggestion for the use of Trichoderma
spp. as biocontrol agent was given by Weindling.
1963 – The first
commercially available bio control agent was Peniophora gigantean for the control of Heterobasidium annosum.
1914 –(03.02.1914) In
India, Destructive insect and Pests Act (DIPA/ DIP ACT) was passed prohibiting
or restricting the import of plant and plant materials, insects, fungi to India
form foreign countries.
1964 – Thirumalachar
reported the development of Aureofungin, a new antifungal antibiotic for use in
plant disease control.
1975 – S.Nagarajan and
H.Singh formulated a set of synoptic conditions called the “Indian Stem Rust
Rules” for predicting possible outbreaks of wheat stem rust.
1980 – S.Nagarajan and
L.M.Joshi defined the route of long distance spread of black stem rust of wheat
between the source and the target as “Puccinia path” of India and also
suggested the possibility of avoiding epidemics by deployment of resistance
genes along this path.
J.E.Vanderplank – Father of
Plant Disease Epidemiology
Paul Neergaard – Father of
Seed Pathology
S.D.Garrett – Father of
Biological Control
Jacov Katan – Father of Soil
Solarization
T.S.Thind – Father of Indian
Fungicides
Edmond Thenard – Father of
Soil fumigation (CS2)
Haberlandt
- Father of Plant tissue culture
N.A.Cobb
– Father of Nematology (American)
Important textbooks/
reference books related to this course
1971 – Y.L.Nene and
P.N.Thapliyal wrote the first book on fungicides in India – “Fungicides in Plant Disease Control”.
(now in 3rd edition)
1984 – S.C.Vyas wrote a
book entitled “Systemic Fungicides”.
1980 – V.K.Agarwal
derived a method known as “NaOH Seed Soak Method” for detection of Karnal and
paddy bunt infection in wheat and rice seed samples. He also wrote a book entitled “Principles of Seed Pathology”. (now in 2nd edition with
J.B.Sinclair)
1974 – The first book
devoted wholly to the subject of biocontrol of plant pathogens was published by
K.F.Baker and R.J.Cook entitled “Biological
control of Plant Pathogens”.
1963 – Publication of
classical book “Plant Diseases: Epidemics and control” by
J.E.Vanderplank
History of Plant Nematology
Needham – Discovery of wheat
seed gall nematode Anguina tritici
Atkinson – 1st report of root knot nematode and Fusarium
complex in vascular wilt in cotton
Hinger - 1st report of root knot nematode and Bacterial wilt in tomato
Hewitt, Raski & Goheen – Transmission of grapevine fan leaf virus
by Xiphinema index
Butler – reported Ufra disease on rice is caused by Ditylenchus angustus
Dastus – reported white tip disease on rice is caused by Aphelenchoides
besseyi
Definition for Plant diseases
·
Disease is a malfunctioning process that is
caused by continuous irritation, which results in some suffering producing
symptoms. (APS & British Mycological Society (BMS))
·
A plant is said to be „diseased‟
when there is a harmful deviation from normal functioning of physiological
process (Federation of British Plant Pathologists).
·
Any malfunctioning of host cells and tissues
that result from continuous irritation by a pathogenic agent or environmental
factor and leads to development of symptoms (G.N.Agrios).
Causes of Plant Diseases
Biotic agents (Animate agents/
Parasitic agents)
1. Prokaryotes
True bacteria or bacteria E.g.. Rice BLB
Rickettsia-like bacteria (RLB / FVB) E.g. Citrus greening,
Pierce's disease of grape
Mollicutes or wall-less prokaryotes
i. Mycoplasma-like organism (MLO)/ Phytoplasma: e.g. Tomato bunchy top, Sesame phyllody
ii. Spiroplasma e.g. Corn stunt, Citrus stubborn
2. Eukaryotes
Fungi E.g. Late
blight of potato
Fungi like Protozoa E.g. Club root of cabbage
Algae E.g. Red rust
of guava
Plants - Parasitic flowering plants or phanerogamic
parasites - Broomrape of tobacco.
Animals- Nematodes Ex. Rice Ufra disease – Ditylenchus angustus.
Mesobiotic
agents
Ex. Viruses and Viroids.
They are infectious agents. They can be crystallized and are considered as non-living.
But their multiplication in the living plants ensures that they are living
(Obligate parasites / Biotroph). Hence they are called as mesobiotic agents.
Viruses E.g. BYVMV
Viroids E.g. PSTVd
Abiotic
agents or Non-parasites / Inanimate agents / non-infectious / physiological disorders
Black heart of potato – O2
deficiency
Sunscald of fruits – High temperature
Blossom end rot of tomato – Ca deficiency
Classification of plant diseases
Based on
type of infection
a. Localized diseases: These diseases are limited to a
definite area of an organ or part(s) of a plant. E.g. Leaf spot
b. Systemic diseases: In these diseases the pathogen spreads
from a single infection point so as to infect all or most of the host tissues. E.g.
Viral diseases
Based on
type of perpetuation and spread
a. Soil-borne diseases: The causal agents perpetuate and spread
through soil. Ex. Damping-off, root rot
b. Seed-borne diseases: Seed or seed materials help in the
perpetuation and spread of this disease.
E.g. Loose smut of wheat (Ustilago nuda tritici internally
seed borne)
Blast of rice (Pyricularia
oryzae externally seed-borne).
c. Air-borne diseases: Anemochory (Most of the foliar
diseases)
d. Water – borne diseases (Hydrochory): Soli borne diseases
Based on
extent of occurrence and geographic distribution
a.
Endemic diseases (enphytotic disease): When a
disease is more or less constantly occurring year after year in a moderate to
severe form in a country or locality then it is called as an endemic disease.
E.g. wart disease of potato (Synchytrium
endobioticum is endemic in Darjeeling)
citrus canker is endemic in Asia
Sorghum rust is endemic in India.
b.
Epidemic or epiphytotic disease: An epidemic or
epiphytotic refers to sudden outbreak of a disease periodically over a
widespread area in a devastatingly severe form causing extensive losses or
complete destruction.
E.g. wheat powdery mildew, rice
Lakshmi / false smut disease
c.
Sporadic diseases: Sporadic diseases are those,
which occur at irregular intervals over limited areas or locations. E.g. Fusarium
wilt of cotton (Fusarium oxysporum f.sp. vasinfectum)
d.
Pandemic diseases: A disease is said to be
pandemic when it is prevalent throughout the country, continent or world
involving mass mortality. E.g. Late blight of potato and wheat stem rust.
Based on
the multiplication of inoculum
a.
Simple interest disease (monocyclic / Saturation
curve): the disease increase is just
like simple interest in money. Here inoculum comes from a reservoir and hence
amount of inoculum for a given season's crop is fixed. So there is no
repetition of the disease cycle within the crop season. Hence the disease
spread will be slow. e.g. Soil inhabiting pathogens like Pythium sp., Rhizoctonia
sp. and Sclerotium sp.
b.
Compound interest disease (polycyclic / Sigmoid
curve/ ‘S’ shaped progress curve): Inoculum is multiplied several times (every
7 to 15 days for wheat rust) during crop growth in a season. So the disease
spread will be fast. e.g. Wheat stem rust, rice blast, powdery mildew diseases
of different crops.
c.
Polyetic disease (Bimodal curve): Several years
are required for completing their life cycle of this pathogen. E.g. Dutch elm
disease, Citrus Tristeza, Pear decline
Based on the crops affected
a.
Sugarcane red rot
b.
Wheat Tundu disease
c.
Club root of crucifers
Based
on the organs affected
a.
fruit rot
b.
Sheath blight
c.
Stem rot
Based on
Host Pathogen dominance system
a.
Pathogen dominant diseases: The pathogen is
dominant over the host, but the relationship is transitory because the
resistance of the host is less initially than it becomes eventually. E.g. Macrophomina, Pythium
b.
Host dominant diseases: The host is dominant and
the pathogen is successfully only, when factors favour the pathogen over the
host. E.g. Fusarium, Helminthosporium
Principles of Plant disease management
Methods for plant diseases management were first classified
by Whetzel (1929) into Exclusion, Eradication, Protection and Immunization.
Further advances in plant pathology leading to development of newer methods, two
more principles - avoidance and therapy were created (NAS, 1968)
a.
Exclusion
b.
Eradication
c.
Protection
d.
Immunization
e.
Avoidance
f.
Therapy
The six principles that characterize the modern concept of
plant disease management should be viewed from three stand points
(a) Reduction in the initial inoculums or the rate of
disease development.
(b) Management of the pathogen population, the cure or
induce defense of the suscept or modify the environment as it influences
disease
(c) Interruption of dispersal, survival or the course of
disease development.
Exclusion
It means preventing
the inoculums from entering or establishing in a field or area where it does
not exist.
Seed
treatment
1.
Seed treatments with Brine Solution (20 % Nacl)
for manage the BLB, Ergot and Tundu disease.
2.
Hot Water Treatment with Sugar cane setts @ 500C for 2-2and half hours for manage the grassy
shoot and ratoon stunting disease.
3.
Hot Air Treatment with Sugar cane setts @ 540C for 8 hours for manage the grassy shoot
disease (HAT).
4.
Aerated Steam Therapy with Sugar cane setts @ 500C for one hour for manage the grassy shoot
(AST).
5.
Moist Hot Air Treatment with Sugar cane setts @
540C for 2 hours for manage
the grassy shoot (MHAT.
Inspection
and certification
Due to the inspection, necessary precautions are taken to
remove the diseased plants, badly affected fields and roguing. By this method,
inter and intra regional spread of seed borne diseases can be prevented,
Quarantine
Ø
Quarantine the word which is derived from Italian
language and means forty days retention period. Plant quarantine is
defined as “a legal restriction on the movement of agricultural commodities for
the purpose of exclusion, prevention or delaying the spread of the plant pests
and diseases in uninfected areas”.
Ø
Plant quarantine laws were first enacted in France (1660),
followed by Denmark (1903) and USA (1912) (Eradication of Barberry bush)
Ø
In India, plant quarantine rules and regulations
were issued under Destructive
Insects and Pests Act (DIPA or DIP Act) in 1914 (03.02.1914).
1. Domestic
quarantine: Rules and regulations issued prohibiting the movement of
insects and diseases and their hosts from one state to another state in India
is called domestic quarantine. Domestic quarantine in India exists for two
pests (Rooted scale and Sanjose scale) and three diseases (Bunchy top of
banana, banana mosaic and wart of potato).
Bunchy top of
banana: It is present in Kerala, Assam, Bihar, West Begal and
Orissa. Transport of any part of Musa species
excluding the fruit is prohibited from these states to other states in India.
Banana mosaic:
It is present in Maharashtra and Gujarat. Transport of any part of Musa species excluding the fruit is
prohibited from these states to other states in India.
Wart of potato:
It is endemic in Darjeeling area of West Bengal, therefore seed tubers are not
to be imported from West Bengal to other states.
2. Foreign
quarantine: Rules and regulations issued prohibiting the import of
plants, plant materials, insects and fungi into India from foreign countries by
air, sea and land. Foreign quarantine
rules may be general or specific. General rules aim at prevention of
introduction of pests and diseases into a country, where as the specific rules
aim at specific diseases and insect pests. The plant materials are to be
imported only through the prescribed ports of entry.
Airports:
Bombay (Santacruz), Calcutta (Dum Dum), Madras (Meenambakam), New delhi (Palam,
Safdarjung) and Tiruchurapalli.
Sea
ports: Bombay, Calcutta, Vishakapatnam, Trivandrum, Madras,
Tuticorin, Cochin and Dhanushkoti.
Land
frontiers: Hussainiwala (Ferozpur district of Punjab), Kharla
(Amritsar district of Punjab) and Sukhiapokri (Darjeeling district of West
Bengal)
3. Embargo:
It is government prohibition against the shipment of certain products to a
particular country for economic or political reasons.
|
Crop
|
Countries from
where import is prohibited
|
|
Coffee
|
Sri Lanka, Africa, South America
|
|
Sugarcane
|
Fiji, Australia, Philippines
|
|
Sunflower
|
Argentina, Peru
|
Phytosanitary
certificate (PSC): It is an official certificate from the country of
origin, which should accompany the consignment without which the material may
be refused from entry.
PEQ- Post Entry Quarantine
ISPM – International Standards for Phytosanitary Measures
PRA – Pest Risk Analysis is done to protect the country’s
agriculture from damages that can be caused by harmful quarantine pests which
can be brought in along with imported commodities.
There are 4 stages of PRA are
1.
Pest Risk initiation
2.
Risk assessment
3.
Risk management
4.
Risk documentation
PFS Order – Plants Fruits and Seeds Order (1984)
FVS Order – Flowers and Vegetable seeds order
PSC – Phytosanitary certificate
IPPC – International Plant Protection Convention (1951)
APHIS – Animal, Plant Health Inspection service, USA
CBD – Convention on Biological Diversity (Rio Conversion,
1992) (Quarantine of invasive species)
Directorate of Plant Protection, Quarantine & Storage
situated at Faridabad, Haryana
National Plant Quarantine station is situated at New Delhi
SPS – Sanitary and Phytosanitary agreement of WTO
Plant Quarantine (Regulation of Import into India) order
2003 under DIP Act
TRIPS – Trading Related Intellectual Property Rights
|
Sl. No.
|
Disease
|
Causal Organism
|
Year
|
Introduced into
|
From
|
|
1.
|
Late Blight of Potato
|
Phytophthora
infestans
|
1883
|
India
|
Europe
|
|
2.
|
Coffee rust
|
Hemileia vastatrix
(Wardia vastatrix)
|
1879
|
India
|
Srilanka
|
|
3.
|
Powdery mildew of crucifers
|
Erysiphe
cichoracearum
|
1910
|
India
|
Srilanka
|
|
4.
|
Wheat flag smut
|
Tuburcinia agropyri
|
1906
|
India
|
Australia
|
|
5.
|
Downy mildew of grapes
|
Plasmopara viticola
|
1910
|
India
|
Europe
|
|
6.
|
Black rot of crucifers
|
Xanthomonas
campestris
|
1929
|
India
|
Holland
|
|
7.
|
Powdery mildew of rubber
|
Oidium heveae
|
1939
|
India
|
Malaysia
|
|
8.
|
BLB of rice
|
Xanthomonas oryzae
|
1964
|
India
|
Philippines
|
|
9.
|
Blast of rice
|
Magnaporthe grisea
|
1918
|
India
|
South East Aisa
|
|
10.
|
Downy mildew of maize
|
Peronosclerospora
sorghi
|
1912
|
India
|
Java
|
|
11.
|
Ergot of Bajra
|
Claviceps fusiformis
|
1957
|
India
|
Africa
|
|
12.
|
Black shank of tobacco
|
Phytophthora
nicotianae
|
1938
|
India
|
Holland
|
|
13.
|
Panama wilt of Banana
|
Fusarium cubense
|
1920
|
India
|
Panama Canal
|
|
14.
|
Bunchy top of Banana
|
BBTV
|
1940
|
India
|
Srilanka
|
|
15.
|
Wart of Potato
|
Synchytrium
endobioticum
|
1953
|
India
|
Netherland
|
|
16.
|
Fire blight of apple
|
Erwinia amylovora
|
1940
|
India
|
England
|
|
17.
|
Golden cyst nematode
|
Globodera
rostochinensis
|
1961
|
India
|
Europe
|
Eradication
of insect vectors
Many crop diseases spread through insect vectors which
transfer the inoculum from one region to another depending on their flight
range. For prevention of entry of a new pathogen exclusion of insect vectors is
also essential.
Eradication
The process
of reducing, inactivating, eliminating or destroying inoculums at the source, either
from a region or from an individual plant in which it is already established is
termed as eradication.
One of the most extensive
eradication operations carried out so far was to get rid of the citrus canker
in the USA during 1927- 35 (Excellent cultural control)
Biological
control (Sanford and Broadfoot)
The reduction of inoculum density or disease producing
activities of a pathogen or parasite in its active or dormant state by one or
more microorganisms, accomplished naturally or through manipulation of the
environment, hoist or antagonists or by mass introduction of one or more
antagonists. (Baker and Cook, 1974)
The mechanisms of Biological control are Competition,
Parasitism, Antibiosis & Lysis.
Example of Antagonistic organisms:
Trichoderma viride –
Fungal Bio Control Agent
Pseudomonas
fluorescens – Bacterial Bio Control Agent
Ampelomyces quisqualis
10 – BCA for Powdery Mildew
1.
Suppressive soil: Soils that suppress certain
diseases due to presence in soil of micro organisms antagonistic
to the pathogen. E.g. Pythium,
Phytophthora, Gaeumannomyces diseases controlled by Suppressive soil. Numerous
kinds of antagonistic microorganisms have been found to increase in suppressive
soils; most commonly, however, pathogen and disease suppression has been shown
to be caused by fungi, such as Trichoderma,
Penicillium, and Sporidesmium, or by
bacteria of the genera Pseudomonas,
Bacillus, and Streptomyces.
2. Mycorrhizae
(VAM or AM): Fungus roots (Frank) to control soil borne diseases. E.g. Glomus, Gigaspora
3.
Cross protection or Pre-immunization: To
introduce the mild strain of the virus in the healthy plant, so that to avoid
the severe strain of the same pathogen. E.g. Citrus Tristeza Virus mild strain
4.
Hypovirulence: Reduced virulence of pathogen
strain as a result of presence of transmissible double stranded RNA. E.g.
Hypovirulent strain of Endothia
parasitica , Hypovirulent strain of Rhizoctonia
solani.
Crop rotation
Continuous cultivation of the same crop in the same field
helps in the perpetuation of the pathogen in the soil. Soils which are
saturated by the pathogen are often referred as sick soils. To reduce the incidence and
severity of many soil borne diseases, crop rotation is adopted.
It is also possible that different crops release such
biochemical substances in their root exudates that either kill the pathogen
directly or encourage development of antagonistic microorganisms.
Uses of crop rotation are 1. Pathogen lives in soil for very
short time, 2. Having short host range, 3. Annual diseases E.g. Panama wilt of
banana (long crop rotation), wheat soil borne mosaic (6 yrs) and club root of
cabbage (7 yrs), etc.
Removal
or destruction of diseased plant organs
1.
Sanitation
Collection and destruction of plant debris from soil will
help in the management of soil borne facultative saprophytes as most of these
survive in plant debris. (to reduce primary inoculum). Burying the debris deep
in the soil turning ploughs also reduces the inoculum.
Late blight of Potato – Tubers and leaves
Mahali disease of arecanut – Infected and Fallen nuts
2.
Rouging
Removal of diseased plants or their affected organs from
field, which prevent the dissemination of plant pathogens. E.g. Loose smut of
wheat and barley, whip smut of sugarcane, red rot of sugarcaneof bajra, yellow
vein mosaic of bhendi, khatte disease of cardamom, etc.
3.
Eradication of alternate and collateral hosts
E.g: Barberry eradication programme in France and USA
reduced the severity of black stem rust of wheat
E.g. Eradication of Thalictrum species in USA to manage
leaf rust of wheat caused by Puccinia
recondita.
Eradication of collateral hosts, such as Panicum repens,
Digitaria marginata will help in the management of rice blast disease (Pyricularia
oryzae)
4.
Heat and chemical treatment of
disease plants
Luthra solar heat
treatment : Its developed against wheat loose smut disease (Ustilago nuda tritici).
o
Wheat seeds are soaked in cold water for 4 hrs
(Morning 8-12 noon)
o
Seeds are dried under sunlight conditions for
the next 4 hrs (12-4 pm)
o
Seeds are treated with Carboxin @ 4-6g/kg of
seeds
Banana suckers are treated or
dipped with Carbendazim solution @ 1.0 % for 5 min. against Panama wilt
disease.
Soil
treatments
1.
Mixed cropping: Root rot of cotton (Phymatotrichum
omnivorum) is reduced
when cotton is grown along with sorghum. Intercropping sorghum in cluster bean
reduces the incidence of root rot and wilt (Rhizoctonia solani).
2.
Summer ploughing: Ploughing the soil during summer months expose soil to hot
weather which will eradicate heat sensitive soil borne pathogens.
3.
Soil amendments: Application of organic amendments like saw dust, straw, oil cake,
etc., will effectively manage the diseases caused by Pythium, Phytophthora, Verticillium, Macrophomina,
Phymatotrichum and Aphanomyces. Beneficial micro-organisms
increases in soil and helps in suppression of pathogenic microbes.
E.g: Application of lime (2500 Kg/ha) reduces the club root
of cabbage by increasing soil pH to 8.5
Application of
Sulphur (900 Kg/ha) to soil brings the soil pH to 5.2 and reduces the incidence
of common scab of potato (Streptomyces scabies).
4.
Changing time of sowing: Pathogens are able to infect
susceptible plants under certain environmental conditions. Alternation in date
of sowing can help avoidance of favourable conditions for the pathogens. Ex:
Rice blast can be managed by changing planting season from June to
September/October.
5.
Seed rate and plant density: Close spacing raises atmospheric
humidity and favours sporulation by many pathogenic fungi. A spacing of 8’X8’
instead of 7’X7’ reduces sigatoka disease of banana due to better ventilation
and reduced humidity. High density planting in chillies leads to high incidence
of damping off in nurseries.
6.
Irrigation and drainage: The amount, frequency and method of
irrigation may affect the dissemination of certain plant pathogens. Many
pathogens, including, Pseudomonas solanacearum, X. campestris pv. oryzae and Colletotrichum
falcatum are readily disseminated through irrigation water. High soil
moisture favours root knot and other nematodes and the root rots caused by
species of Sclerotium, Rhizoctonia, Pythium, Phytophthora, Phymatotrichum,
etc.
7.
Fallowing : Wilt of Banana and green ear
8.
Flooding : Panama wilt of Banana
9.
Heavy application of FYM – Wilt of cotton
Manures
and fertilizers
Excessive nitrogen application aggravates diseases like stem
rot, bacterial leaf blight and blast of rice. Nitrate form of nitrogen
increases many diseases, whereas, phosphorous and potash application increases
the resistance of the host.
Protection
The protection of infection courts against the inoculums of
many fast spreading infectious pathogen, brought by wind from neighboring
fields or any other distant place of survival.
Protection
from Anemochory diseases
Application of fungicides by dusting and spraying to be
controlled for rust, leaf spot, powdery mildew and downy mildew. The covering
of fungicides upon host surface prevents germination of spores and subsequent
penetration.
Protection
from seed borne diseases
The seed treatment fungicides (seed protectant) from a
protective coat on the seeds so as to protect the seeds from soil borne
pathogens when sown in soil as well as seed borne pathogens. .
Protection
from soil borne diseases
Physical method
1.
Soil
solarization: Irrigate the soil up to a depth of 10 cm and cover the soil
with polythene sheet (100 m) after 2 days of irrigation. Leave the sheet
undisturbed upto 4-6 weeks. Remove the cover and disturb the soil for further
sowing or planting.
2.
Streaming:
In foreign countries, stream is passed through upper soil layers with
perforated tubes fixed below the soil layer.
3.
Direct
flaming: Burning plant residues and wood is effective manage the crop
diseases. E.g. Red rot of sugarcane
4.
Hot water: E.g. Hot water treatment of Cabbage
seeds @ 500 C for 30 min against the black rot of cabbage.
Chemical method: Carbendazim
@ 0.1 % effectively prevent cotton root rot. Soil drenching with 1 % Bordeaux
mixture against Coconut wilt, Pepper wilt, Betel vine wilt.
Biological method: Bio
control agents also protect the seeds from infection by the pathogen, present
in the soil.
Immunization
Improving or inducing the resistance of the host. The best
way of controlling the disease is by the selection and planting of resistance
varieties (Cheapest method of plant disease control).
Methods of developing resistant varieties
- Introduction
- Pure line selection from the susceptible populations
- Breeding by crossing and hybridization
- Mutation using X ray, UV rays, Gamma rays and chemical mutagenic agents.
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Sl. No.
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Characters
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Vertical
resistance
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Horizontal
resistance
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1.
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Controlled by genes
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Major genes
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Minor genes
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2.
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Stability
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Instable
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Permanent
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3.
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Resistance
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Specific pathogens or races
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Many Pathogens
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4.
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Other names
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Monogenic, R gene, Oligogenic, specific resistance,
Perpendicular resistance, Physiological resistance, seedling resistance,
hypersensitivity
or qualitative resistance
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Polygenic, general or nonspecific resistance, polygenic,
minor gene, mature plant, adult,
quantitative resistance, partial or field resistance or
tolerance
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5.
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Resistance power
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Complete resistance
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Incomplete or partial resistance
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6.
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Pathotype specific
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Race specific
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Race non specific
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7.
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Stage of expression
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Seedling to Maturity
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As adult plant
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8.
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Selection and evaluation
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Relatively easy
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Relatively difficult
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9.
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Risk of Boom and Burst
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Present
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Absent
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10.
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Suitable for hosts
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Annuals not perennials
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Both Annuals and Perennials
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11.
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Suitable for pathogen
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Immobile pathogens and not mobile pathogens
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Both mobile and immobile pathogens
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12.
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Efficiency
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Highly efficient against specific races
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Less efficient against all races
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13.
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Existence of gene for gene hypothesis
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Yes
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No
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14.
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Resistance confers
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VR confers complete but impermanent protection
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HR confers incomplete but permanent protection
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15.
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Mathematical model
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Vertical axis of the graph
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Horizontal axis of the graph
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Resistance
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Structural
resistance
1. Waxes and cuticles : Potato leaves with hair are resistant to
late blight.
Linseed varieties
are resistant to Melampsora lini have
thick cuticle.
Barberry
species resistant to wheat smut have thick cuticle and more waxy layer.
2. Cell wall / Endodermis : Potato
varieties resistant to Pythium have more root fiber. In rice varieties
resistant to blast fungus have more Silicic acid.
Functional
resistance
·
Irregular blossom opening is the main factor for
absence of ergot disease in wheat.
·
Short or less time stomata opening citrus
varieties are resistant to citrus canker disease for avoid the entry of
pathogen.
Chemical
resistance
·
Older beans are resistant to anthracnose because
of alkaline pH.
·
Grape vine varieties resistant to powdery mildew
have more tannic acid.
Nutrition
·
The ground nut varieties are resistant to tikka
disease have more riboflavin content.
·
High sugar diseases : Rust and Powdery mildew
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Low sugar diseases : Early blight
Toxic
principles
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Red coloured onions are resistant to smudge
disease due to catechol, protocatechuic acid.
·
Gram varieties are resistant to Ascochyta rabiei due to the presence of
mallic acid
·
Potato varieties are resistant to scab and late
blight contain more chlorogenic acid solanin
·
Lime varieties are resistant to die back due to
the presence of isopimpinellin
·
Tomato varieties are resistant to Septoria and Alternaria due to the presence of Tomatin
Active
structural (Direct Protection)
1.Callose deposition :
Barley varieties are resistant to powdery mildew
2. Lignification: Lignin
are formed around the hyphae and thereby further penetration is avoided. E.g.
Take all disease
3. Wound barriers: After
infection in plant cells, corky layers are formed to prevent further invasion.
4. Hypersensitivity / PCD : it’s a quick defense mechanism
of plants after the infection process.
5. Phytoalexins : Capsidiol, Gossypol, Pisatin
Important
resistant varieties
Rice blast: ADT 36, ADT 37, ADT 39
Rice brown spot : CO44
Rice Tungro: IR 50, CO 45
Ground nut tikka and rust : ALR 1, ALR 3
Black gram yellow mosaic: VBN 1, VBN 3
Sugar cane red rot: COC 99061, CO 86249
Potato late blight: Kufri Jyothi
Bhendi yellow vein mosaic: Arkha anamika, Parbhani kranti
Angular leaf spot of cotton: MCU 10
Avoidance
It involves avoiding disease by planting at time when, or in
areas where inoculums is absent or ineffective due to environmental conditions.
1. Proper selection of
geographical area: Cumbu ergot (wet areas)
2. Selection of field:
Sugar cane red rot, downy mildew of cumbu
3. Choice of time of
sowing: Late sowing are increases the incidence of wheat stem rust disease.
4. Disease escaping
varieties: Early maturity varieties are resistant against wheat stem rust
disease
5. Selection of seed
and planting stock : Potato viral diseases
.
Therapy
Reducing severity of disease in an infected individual.
Chemotherapy: chemicals are used for chemotherapy are
systemic fungicides and antibiotics.
Heat therapy (Luthra and Sattar Solar Heat treatment – Wheat
Loose smut)
Tree surgery (Chaubattia paste)
Prophylaxis
Exclusion (Quarantine and other legislative measures)
Eradication (Cultural eradication and Chemical eradication)
Protection (Cultural manipulation, Physical and chemical
protections)
Immunization
Genetic resistance
Therapy (Physical and chemical therapy)
