PLANT PATHOLOGY Disease - When there is a harmful deviation from normal functioning of physiological process. CLASSIFICATION OF PLANT DISEASE 1. Non-infectious diseases • Diseases with which no animate or virus pathogen is associated. • Cannot be transmitted. • No parasite is associated (Non-parasitic diseases). Ex. Tip rot or Necrosis of mango - B deficiency. Black heart of potato - Oxygen deficiency. Khaira disease of paddy - Zn deficiency 2. Infectious diseases • A specific pathogen is responsible for the diseases. • diseases are infectious, contagious and transmittable Koch's postulates are: 1. The pathogen must show constant association with the disease. 2. The pathogen must be isolated from the diseased host and grown in pure culture. 3. The pathogen from the artificial culture should be able to reproduce the disease when inoculated on healthy plant of the same kind. The symptoms produced should be identical with those seen on the plant from which isolation was made. 4. The artificially produced disease should yield the same pathogen on reisolation. Infectious diseases are often classified according to their occurrence in the following groups - Fungi, Bacteria, Virus, Viroids, Phytoplasma, Spiroplasma, Fastidious vascular bacteria, Nematode. Agri optionals agademy.in of 1 43
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PLANT PATHOLOGY - Agademy · Khaira disease of paddy - Zn deficiency 2. Infectious diseases • A specific pathogen is responsible for the diseases. • diseases are infectious, contagious
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PLANT PATHOLOGY
Disease - When there is a harmful deviation from normal functioning of physiological process.
CLASSIFICATION OF PLANT DISEASE
1. Non-infectious diseases • Diseases with which no animate or virus pathogen is associated. • Cannot be transmitted. • No parasite is associated (Non-parasitic diseases).
Ex. Tip rot or Necrosis of mango - B deficiency. Black heart of potato - Oxygen deficiency. Khaira disease of paddy - Zn deficiency
2. Infectious diseases • A specific pathogen is responsible for the diseases. • diseases are infectious, contagious and transmittable
Koch's postulates are: 1. The pathogen must show constant association with the disease. 2. The pathogen must be isolated from the diseased host and grown in pure culture. 3. The pathogen from the artificial culture should be able to reproduce the disease when
inoculated on healthy plant of the same kind. The symptoms produced should be identical with those seen on the plant from which isolation was made.
4. The artificially produced disease should yield the same pathogen on reisolation.
Infectious diseases are often classified according to their occurrence in the following groups - Fungi, Bacteria, Virus, Viroids, Phytoplasma, Spiroplasma, Fastidious vascular bacteria, Nematode.
Eukaryotic protist, achlorophyllus, nucleated, branched, unicellular or multicellular organisms that may reproduce by the division of vegetative cells, well defined asexual and sexual spores. Body of the fungus is called as 'Thallus'.
GENERAL SYMPTOMS OF FUNGAL DISEASES
1. Damping off • Rotting of seeds and radicle before seedling emergence – Pre-emergence • Rotting of emerged seedlings at ground level resulting in toppling down of seedlings –
Post-emergence • Eg. Damping-off of vegetable - Pythium aphanidermatum P. debaryanum P. ultimum
2. Club root • Modification of roots and rootlets into club shaped swellings due to hypertrophy and
hyperplasia • Eg. Club root of cabbage : Plasmodiophora brassicae
3. Root rot • Disintegration or decay of roots • Eg. Root rot of pulses Macrophomina phaseoina
4. Foot rot • Disintegration of basal part of the stem • Eg. Foot rot in pepper Phytophthora palmivora
4. Collar rot • Collar region of the seedlings rot • Eg. Collar rot of groundnut – Aspergillus niger A.pulveruilentus
5. Stem rot • Leads to rotting Disintegration of the tissues of the stem. • Eg. Stem rot of paddy – Sclerotium oryzae
6. Wilt • Loss of turgidity and dropping of leaves and shoots • Eg: Red gram wilt – Fusarium oxysporum f.sp. udum
7. White rust • White or creamy, shiny irregular pustules seen on the lower surface of the leaves. • Eg. White rust of amaranthus - Albugo bliti
9. Powdery mildew • Small irregular powdery patches are seen on the upper surface of the leaves. • Eg. Powdery mildew of blackgram – Erysiphe polygoni.
10. Leaf spot • Localised necrotic lesions on host leaves. • The spots vary in size, shape and colour
11. Leaf blight • Rapid browning and death of leaves giving a burnt appearance • Eg. Leaf blight of sorghum – Exerohilum tursicum
12. Blast • Spindle shaped spots with grey centre and brown margin appear on leaf (leaf blast) • Blackening of node of the plant (node blast) and neck of the panicle (neck blast) • Eg. Blast of paddy – Pyricularia grisea
13. Anthracnose • Black sunken lesion circular to angular are seen on leaves, cotyledons, stem, fruits, flowers
and pods of plants. • Acervuli the asexual fruiting body is produced in the sunken lesion. • Eg. Anthracrose of bean – Colletotrichum lindemuthianum.
14. Rust • Raised reddish brown (rusty) pustule appear on both surface of leaf, stem etc • Eg. Sunflower rust - Puccinia helianthi
15. Scab • Slightly raised or sunken lesion with cracks on petiole, pedicel, blossom, fruit, leaves and
gives a scabby appearance. • Eg. Scab of apple - Venturia inaequalis
16. Sooty Mould • Superficial dark black sooty growth found on leaf, stem and fruits. • Eg. Sooty mould in mango – Capnodium mangiferae
17. Gummosis • Exudation of gummy substances from infected bark and bark completely rots and dries due
to girdling • Eg. Gummosis of citrus – Phytophthora citrophthora
27. Chlorosis • Loss of chlorophyll giving pale green appearance is the green plant parts.
28. Necrosis • Killing of plant tissue often result in development of brown to black colour.
29. Discolouration • Change in colour of the plant or one or more its pacts
BACTERIA
Bacteria are unicellular, microscopic, chlorophyll less, prokaryotic microorganism reproduce mainly by fission.
SYMPTOMS OF BACTERIAL DISEASES
Plant pathogenic bacteria are basically facultative saprophytes and they enter into the host plant mostly through wounds and natural openings. The important symptoms are
1. Leaf spot • Symptom include the appearance of water soaked, circular or irregular, necrotic spot on
leaves. Sometimes the spots are encircled with a yellow halo. • Dicot - spot is restricted by veins and become angular. • Monocots - spots usually appears as streaks or stripes.
Eg. Bacterial leaf spot in tomato : X. axonopodis. pv. vesicatoria, Angular leaf spot in cotton : X. a. pv. malvacearum Bacterial leaf streak in paddy : X. oryzae. pv. oryzicola
2. Leaf blight • Rapid and extensive necrosis of affected leaves resulting in scorched appearance.
(Eg) Bacterial blight in paddy : X. oryzae. pv. oryzae Bacterial blight in beans : X.c. pv. phaseoli.
3. Soft rot • Affected area is soft, watery, discoloured and somewhat depressed, or wrinkled or
blistered. • Eg. Soft rot of tomato, egg plant, crucifers, onion, carrot, celery, lettuce is caused by
4. Canker • Formation of corky outgrowth on the surface of leaves, swigs and fruits as a result of
necrosis of host • Eg. Citrus canker : X. axonopodis. pv. citri, • Bacterial canker in mango : X. a. pv. mangiferae indica
5. Scab • The infected area becomes rough, corky, slightly raised with rusty surface and pitted due to
the abnormal proliferation of tissues in the epidermis. • It is only by epidermal infection and are not deep seated. • Eg. Potato scab: Streptomyces scabies
6. Galls and tumours • Development of elongated (or) irregular targe sized outgrowth on the affected plant part
due to the hypertrophy and hyperplasia of cell. • Hypertrophy - abnormal increase in size of individual cells • Hyperplasia - abnormal increase in number of cells • Eg. Crown gall in apple – Agrobacterium tumefaciens.
7. Wilt • Yellowing, dropping, wilting and death of the above ground parts of the plant. • Bacteria enter and multiply inside the xylem vessels of host plant. • The occlusion of vessels by bacterial cells and their polysaccharides interfere with
translocation of water and nutrients and Wilt symptom develops. • Eg. Bacterial wilt in solanaceous plants : Pseudomonas solanacearum • The wilted plants show brown to black colour discolouration in vascular bundle.
Virus particles consist of nucleic acid encapsidated within a protective protein coat called capsid. Capsid is made up of individual subunits called capsomeres. Mature virus particle is called virion. It is obligate in nature
Common symptoms
1. Reduction in growth • Reduced plant height • Almost all parts show reduction
2. Mosaic and related symptoms • Development of patternof dark green and light green areas giving mosaic effect • Seen on leaves and fruits • Eg. Tobacco mosaic virus, Cucumber mosaic virus
3. Chlorosis • Whole leaf become yellow due to loss of chlorophyll • Chlorosis confined to the vein – Vein clearing • Eg. Bhendi yellow vein virus
4. Ringspotting • One or more concentric rings of dead cells with normal green tissue between them • Eg. Tobacco ring spot virus, Papaya ring spot virus, Tomato spotted wilt virus
5. Necrosis • Death of tissue, organs or whole plant • Eg. Potato virus X, Potato virus Y
6. Abnormalities in growth of leaves • Texture of leave become thick and brittle • Veins become unusually thickened • Leaves become smaller, malformed and blistered • Shoe string – Leaves becomes thread like • Leaf rolling • Eg., Papaya ring spot virus, CMV on tomato
7. Enation or tumours • Outgrowth from upper or lower surface of leaves • Eg. Pea enation mosaic virus
8. Symptoms on stem and Roots • Tumours are produced on the stem and roots of woody plants • Eg. Cocao swollen shoot virus – Swollen stem on cocao plant • Wound tumour virus – Tumours on roots of clover
9. Flower symptom • Color breaking on flowers • Reduced size, deformed shape and reduced flowering • Eg. Tulip color breaking virus
10. Abnormalities in Fruits, Seeds and Pollens • Color change on fruits, Mottling, ring spotting and necrotic symptoms, distorted
and mishappened • Eg. Cucumber mosaic virus on cucumber • Tomato spotted wilt virus on groundnut leads to reduced kernel size
Satellite Viruses
• Viruses which depend for their replication on HELPER VIRUSES • Eg., Tobacco necrosis satellite virus (sTNV), which has a small piece of ssRNA which
codes only for a capsid protein, and depends for its replication on the presence of TNV.
Diseases resembling virus diseases
Viroids • Viroids are circular, single stranded pathogenic RNAs of few hundred nucleotides long
(240 – 400nt) smallest of known agents of infectious diseases. • They do not code for any protein and are replicate independently of any associated
plant virus • They lack protein coat
Important diseases caused by viroids are, • Potato spindle tuber viroid (First viroid disease by Diener, 1971) • Citrus exocortis viroid • Coconut cadang cadang viroid • Tomato bunchy top
Phytoplasma • Lack true cell wall, bounded by single triple-layered membrane, gram negative, cells
containing cytoplasm, randomly distributed ribosomes and strands of nuclear material. • Exhibit pleomorphic shape • Reproduce by budding and binary fission • Lack flagella and do not produce pores • Resistant to penicillin and sensitive to tetracycline, chloramphenicol and erythromycin
• Transmitted by leaf hoppers • Not culturable – Koch’s postulate not proved
Important phytoplasma diseases are, • Little leaf of brinjal (Vector: Hishimonus phycitis) • Gingelly phyllody (Vector: Orosius albicinctus) • Rice yellow dwarf • Grassy shoot of sugarcane • Coconut root wilt (Vector: Lace wing)
Spiroplasma • Gram positive, Pleomorphic cells, varying in shape and helical in form • Lack true cell wall bounded by triple layered membrane • Require sterol for its growth • Culturable on nutrient media and multiply by fission • Susceptible to tetracycline but not to penicillin
Important Spiroplasma diseases are, • Corn stunt (Vector: Dalbulus maidis, D. elimatus – Leafhopper) • Citrus stubborn (Vector: Circulifer tenellus)
Fastidious vascular bacteria • Previously called as rikettsia like organism (RLO) • Cause plant diseases and cannot be grown on artificial media • Limited only fastidious to xylem/phloem.
1. Stem parasite Total parasite - Cuscuta Semiparasite - Loranthus
2. Root parasite Total parasite - Orabanche Semiparasite – Striga
EPIDEMIOLOGY
Edpidemiology or epiphytology is the study factors influencing the outbreak of an infectious disease
• Endemic – A disease which more or less present constantly from year to year in a particular area – Eg. Potato wart disease in Darjeeling area, Club root disease of cabbage is endemic in the Nilgiris district
• Sporadic – A disease when occurs at irregular intervals, locatio and in relatively few instances – Eg. Angular leaf spot of cucumber, Udubatta disease in rice
• Epidemic / Epipytotic – A disease which occurs in a severe form over a larger area for a limited period – Eg. Brown spot of rice, Powdery mildew disease in grapevine
• Pandemic – When a disease is prevalent through out the country, continent or world – Eg., Late blight of potato, coffee rust, Damping off disease in Tomato. An epidemic may cause widespread and mass destruction of crop in a short time or may
persist for long periods depending upon the three following factors responsible for the disease:
Types of Epidemics Rapid Epidemic / Compound interest disease
Pathogen multiply at a higher rate with in a short period leads to rapid increase of disease Eg. Late blight of potato, Stem rust of wheat, Powdery mildew of wheat Slow epidemic / Simple interest disease
Infection take several years to become epidemic – Eg. Vascular wilts, Soil borne smuts Causes of epidemic
i. Inoculum potential ii. Unnatural culture iii. Introduction of a disease to a new area – Eg. TN1 rice variety from Japan – BLB
susceptible iv. Due to plant breeding – Eg. HB3 Cumbu – highly susceptible to downy mildew
v. Weather factors a. Temperature
Powdery mildew favoured in summer BLB – Temp around 25-30oC (not below this temp) Apple Scab – temp is near 20oC and blossom remain wet for 18hrs
b. Relative humidity Sorghum downy mildew – maximum sporulation @ 100% RH Late blight of potato – temp of 10oC & RH not less 75%
c. Rainfall Frequent drizzling favours cumbu ergot BLB – combination of rainy weather, strong wind & temp of 22-26oC Brown spot of rice – Heavy rainfall accompanied by temp of 25-30oC, cloud weather & low solar radiation
d. Dew Sorghum downy mildew - more sporulation @ leaves are wet for 4-5hr Blast – Dew for 6-8hrs favours disease
e. Light Heavy shade – increases brown spot of rice, Blister blight of tea More sporulation of cumbu downy mildew @ Increased light duration
Host Pathogen Environment
❖ Susceptibility of the host ❖ A g g r e g a t i o n a n d
distribution of susceptible hosts
❖ Introduction of new hosts ❖ I n t r o d u c t i o n o f n e w
collateral or alternate host
❖ Introduction of a new pathogen ❖ Presence of aggressive strain of
the pathogen ❖ High birth rate of the pathogen ❖ Low death rate of the pathogen
b. Soil Temperature Verticillium wilt of cotton – low soil moisture (<20 oC) Fusarial wilt – hight soil moisture (>32 oC)
c. Soil pH Acid soil – Favours Club root of cabbage Alkaline soil – Fusarial wilt of cotton, Common scab of potato
DISEASE SURVEY AND ASSESSMENT Methods of Survey
i. Fixed plot survey Select two villages and fix two fields per village. Select 5 sampling plots per field of one acre away from bund. Sample plot size is 1sq. m. Select 20 plants or leaves per plot.
ii. Roving survey Select four villages and fix two fields in each village. Observe and score 100plants or leaves by walking across field in each field.
Disease surveillance reports i. White card – Contains disease / pest surveillance detail in a particulr block/ division /
district for a week. ii. Yellow card – When the disease / pest occurrence attained half the level of ETL iii. Red card - When the disease / pest occurrence exceeded ETL
Disease assessment 1. Assessment in terms of percentage
Applicable for disease which cause complete death of plants (Eg. Damping off, Root rot, wilt, etc.), systemic diseases (eg. Virus, Phytoplasma, etc.,) and in diseases leading to total destruction of infected organs (eg., Smut, greenear, etc.,)
Percent disesase incidence = (No. of plants infected / No. of plant observed) x 10
2. Assessment using disease grades Applicable for the foliar diseases like downy mildew, powdery mildew, leaf spot, leaf blight, canker, rust, etc. Sum of all numerical ratings 100
GENERAL PRINCIPLES OF DISEASE MANAGEMENT Controls must be based on knowledge of the specific diseases, pathogen life cycle, time and method of infection, plant parts affected method of causal agent dissemination and organic considerations. Six fundamental principles of disease management are
Exclusion • Plant disease legislation • Inspection of plant product • Elimination of pathogen from planting material
Eradication • Direct removal of pathogen • Elimination by actual practices • Destruction of pathogen
Avoidence • Choice of geographic area • Selection of field • Time of sowing • Disease escape
o IR-50 susceptible host to blast – sown during summer escaped from blast. • Selection of seed and planting materials • Modification of cultural practices
o Closer spacing increase – Powdery mildew, sigatoka disease o Less shade –increase – tea blister blight and coffee rust o Mixed cropping of pulse and Cumbu reduce yellow mosaic incidence.
Exclusion • Exclusion is to prevent the spread of disease when avoidance failed • It can be achieved by
• Destructive insects and pests act, 1914 – India. • Quarantine offices in India – Mumbai, Cochin, Chennai, Calcutta, Vizagapattinam. • Airports – Amritsar, Mumbai, Chennai, Calcutta, New Delhi. • NBPGR – National Bureau of Plant Genetic Resources involved in import / export
of plant materials.
CLASSIFICATION OF QUARANTINE • Exclusive – Prohibition of importation of plant materials. • Regulatory – import permitted if accompanies “Phytosanitary certificate” Also
DOMESTIC: Restricts spread of a disease with in a country from one place to another with in state or between states.
• In TN Madras Agricultural pests and diseases Act, 1919 - Control of sandal spike, Cardamom mosaic, Orabanche, Wheat stem rust, blister blight.
• In INDIA DIP Act 1914 – Prevent spread of BBTV from Assam, Kerala, Orissa, Tamil Nadu and
west Bengal. – Prevent spread of potato cyst nematode from TN.
INTERNATIONAL (Foreign) • Coffee leaf rust – Hemilieavastatrix (Srilanka)- 1940 • Late blight of potato – Phytophthorainfestans(Srilanka)- 1883 • Banana bunchy top virus- (Srilanka)-1940 • Paddy blast- (Srilanka)-1918 • Cardamom suckers – prohibited from Anamalais to avoid Katte mosaic virus
Embargo Total prohibition on import or export of transport of plant material in a country.
Categorization of quarantine restrictions: • Unrestricted • Restricted – require phytosanitary certificate • Post entry quarantine • Prohibited – require phytosanitary certificate and import permit
Eradication Aims at killing of pathogen that have already gained entry in to the country. Eradication from seeds and seed materials Mechanical
▪ 20% brine solution Physical
▪ Steam at 52 – 540 c for 20 mins – ex. BLB and Blast ▪ Sugarcane grassy shoot – hot water treatment 500 c for 2 – 2.30 hrs ▪ Hot air @ 500 c for 8 hrs ▪ Aerated steam theraphy at 500 c for 1 hr
▪ Moist hot air treatment – 54 0 c for 2 hrs ▪ Luthra solar treatment – loose smut of wheat.
Chemical Biological
Eradication of infected / diseased plants i. Sanitation ii.Surgery and rouging iii.Eradication of alternate host / collateral host iv.Crop rotation
Successful for a. Pathogens live in soil for short time b. Having short host range c. Annual diseases
Eg. Cotton wilt – Paddy Redgram wilt – Paddy Potato brown rot – Wheat Club root – Wheat and Potato Green ear of cumbu – Pulses / Cotton
v.Mixed cropping vi.Modifying soil reaction
a. Application of lime –Reduces club root of cabbage & Brown rot of potato b. Application of Gypsum – Reduces Potato scab & wilt of cotton
vii.Cultural practices viii.Eradications of pathogens in soil
Protection – Accomplished by the application of chemicals to the plats i. Protection from air borne disease ii. Protection from seed borne disease iii. Protection from soil borne disease
a. Physical method - Soil solarisation – Irrigate field upto 10 cm depth and cover the soil with
polythene sheet after 2 days of and leave it undisturbed for 4-6 weeks. - Steaming - Direct flaming – Burning plant residues to manage disease caused
Pythiumspp. and Red rot. - Hot water
b. Chemical method c. Biological method
Immunization – Process of developing resistance in plants to diseases - Best way is planting resistant variety - Immune plants never affected by the pathogens
Resistance – Ability of the plant to reduce or retard the attack of pathogen Methods of developing resistance variety
ii. Pureline selection iii. Crossing and hybridization iv. Mutation – X ray, UV, Gamma & chemical mutagens
Important resistant varieties
Paddy: Blast – ADT 36, 37, 39, 40, 43, Co 37, Co 43, Co 44, Co 45, Co 47, IR 64, Ponmani, IR 20, ASD 16 Brown spot – Co 20, Co 44, Bala, Bhavani BLB – IR 20, Zenith, IR 28, 29, 30 RTV – IR 20, 28, 29, 30, IR 50 and Co 45
Sorghum: Downy Mildew – QLSCO 25, CO 26, CO 21 Wheat: Stem and Yellow rust – Lerma Roja, Safed Lerma, Sonalika, Choti Lerma
Yellow rust – Hira Brown rust – Pratap Yellow and Orange rust – VP 262 Loose smut – Kalyani 277, PV 18, WG 307, C 302
❖ Fungicide is a chemical capable of killing fungi ❖ Fungistat - chemicals do not kill but simply arrest the growth of the fungus ❖ Antisporulant - chemicals that inhibit the spore production without affecting the
1. Protectant - effective only if applied prior to fungal infection eg., Zineb, Sulphur 2. Therapeutant - Capable of eradicating a fungus after it has caused infection and there by
curing the plant eg. Carboxin, Oxycarboxin antibiotics like Aureofungin 3. Eradicant - eradicate the dormant or active pathogen from the host. eg. Organic
mercurials, lime sulphur, dodine etc.
Based on general use 1. Seed protectants: Eg. Captan, thiram, organomercuries carbendazim, carboxin etc. 2. Soil fungicides (preplant): Eg. Bordeaux mixture, copper oxy chloride, Chloropicrin,
1. Bordeaux mixture • It is prepared by mixing copper sulphate and lime in water (to get 1% mixture, mix 1 kg of CuSO4 and 1 kg of lime in 100 litres of water)
• CuSO4+Ca (OH) 2 ----------> Cu (OH) 2 + CaSO4 • Phytotoxic to apple, pear, peaches and high yielding
varieties of Rice, Maize
2. Bordeaux paste It is prepared by mixing 1 kg of CuSO4 and 1 kg of lime in 10 litres of water.
3. Burgundy mixture It is prepared by mixing 1 kg of CuSO4 and 1 kg of Sodium Carbonate in 100 litres of water,
4. Cheshnut compound It is prepared by mixing 2 parts of copper sulphate and 11 parts of Ammonium Carbonate
II. Copper carbonate preparation
Chaubattia Paste This is prepared by mixing 800 g of copper carbonate and 800 g of Red lead in 1 litre of linseed oil or lanolin.
i. Acetamides: e.g., cymoxanil ii. Acylalanines: e.g., Metalaxyl, Furalaxyl, Benalaxyl iii. Pyrimidines and purines: e.g., Dimethirimol, Ethirimol iv. Triazoles: e.g., R.H-24, Tricyclozole, Fluotrimazole, Triadimefon, v. Phenol derivatives: e.g., Chloroneb
13. Antibiotics Chemical substance produced by one microorganism which in low concentration can
inhibit or even kill other microorganisms. Antibacterial antibiotics
o Produced from Streptoverticillium o Given as soil drenching and foliar spray. o As a truck application/root feeding, 2 g of aureofungin-sol+1g of copper sulphate in 100 ml
of water effectively reduce Basal stem end rot of coconut. o Trade name: Aurefungin-Sol.
2. Griseofulvin o Produced by Penicillium griseofulvum. o Tradename: Griseofulvin, Fulvicin and Grisovin. o Highly toxic to powdery mildew of beans and roses, downy mildew of cucumber. o Control Alternaria solani in tomato Sclerotinia rot in apple and Botrytis rot in lettuce.
3. Cycloheximide o Produced by different species of Streptomyces, o Trade Name: Actidione, Actidione PM, Actidione RZ and Actispray.
4. Blasticdin o Product of Streptomyces griseochromogenes o Specifically used against blast disease of rice caused by Pyricularia oryzae. o Trade Name: Bla-s.
5. Antimycin o Produced by several species of Streptomyces, o Effectively used against early blight of tomato, rice blast and seeding blight of oats. o Trade Name: Antimycin.
6. Kasugamycin o Obtained from Streptomyces kasugaensis. o very specific antibiotic against rice blast disease.
• Initially formation of reddish brown specks on the leaf blade. • Later specks enlarge to form spindle shaped lesions with reddish brown margin and grey
centre. • Later the lesion coalesces and leads to drying of entire leaf.
2. Nodal blast/nodal infection • Black discoloration on the nodal region.
3. Neck blast/rotten neck • Initially black discoloration on the neck region. • Weakening of the tissue in the neck region - ear heads are broken and hang down.
4. Grain blast • Black irregular lesion on the grain is seen.
• Compared with healthy plants, infected plants are pale yellow, thin and lanky • Taller than the healthy plant and mature early. • Adventitious roots are seen in the 2nd and 3rd adventitious roots.
• Kresek / wilting: wilting of entire plant within 30 days after transplanting. • Leaf blight: water soaked lesion at the tip of the leaf. • Later it leads to drying of the leaf from tip to bottom with wavy margin.
Management: • Seed treatment and foliar spray with Streptomycin sulphate - 200ppm. • Copper hydroxide – Kocide
WHEAT 1. Black stem rust: Puccinia graminis f.sp. tritici
• Seen only on the stem. Initially linear, elongated reddish brown raised pustules. Later it turns to black raised linear pustules.
2. Brown / orange leaf rust: Puccinia graminis fsp.recondida • Mostly seen on the leaves. Reddish brown/orange raised pustules scattered on the leaf
surface. Later the orange pustules turn to black lesion.
3. Leaf yellow stripe rust: Puccinia graminis fsp.striformis • Mostly seen on the leaves. Yellow, linear and elongated raised stripes on the leaf surface.
Later it turns to black elongated stripes. Management
Symptoms • Exudation of yellow, slimy liquid from individual spikelets. Oozing is deposited on the
stalk of the ear head, stem as well as surface of the leaves. After drying, tissues are malformed and twisted of leaves. Presence of nematode galls is seen on individual grains.
• Tundu disease / Yellow ear rot – Action of both bacteria and nematode • Ear cockle disease – Nematode alone
Management: • Soak the seeds in brine solution -10%, remove the floating infected grains and wash the
good seed with running tap water. • Seed treatment with streptomycin sulphate – 200ppm.
Other important diseases: • Flag smut : Urocystis tritici • Rough spored bunt or Stinking smut : Tilletia caries • Smooth spored bunt: Tilletia foetida • Karnal bunt: Neovassia indica • Foor rot: Pythium graminicolum and P. arrhenomanes • Powdery mildew: Erysiphe graminis var. tritici
• Downy mildew: White downy growth on the lower surface of the leaf. Yellow discoloration on the corresponding upper surface.
• Leaf shredding: formation of chlorotic streaks along the veins due to oospore formation. Shredding of the leaves along the veins at the final stage of the crop growth.
• Seen only at the flowering phase when crop is subjected to moisture stress. Lodging of the plants. When we split open the base of the culm internal portion is fibrous and hallow with black vegetative structures namely the sclerotia and pycnidia.
Management: Frequent irrigation at the time of flowering phase.
3. Rust disease: Puccini sorghi Symptom:
• Reddish brown raised pustules on the leaf surfaces. • Later the reddish brown pustules turn to black pustules.
Management: • Foliar spray with carboxin or oxycarboxin 0.1%
4. Ergot/ sugary diseases: Claviceps purpurea • Symptoms: • Mostly seen when the flowering phase coincides with the winter season. • Characteristic honey dew secretion from individual spikelets. • Each spikelets is converted into black ergot/sclerotia.
• Yellowing and drooping of the plants. • Partial wilting or entire wilting of the plant is seen. • Pink discoloration in the vascular region is the characteristic symptom.
Management: • Spot soil drenching with copper oxychloride @0.25%.
• Reduction of leaf size and proliferation of auxillary buds. • Sterility of the plant is also observed.
Management: • Spraying of dicofol-0.1%, inorganic sulphur.
6. Yellow mosaic: Pigeon pea yellow mosaic virus. Symptom: plants become stunted and on the leaves alternate patches of yellow and green discoloration is observed.
Symptoms: • On the pods initially water soaked lesion appear. • Later it turns to brown and enlarge into circular spots. • Spots are depressed at the centre with reddish brown margin and black centre.
• Pre emergence: Rotting of the seeds before the emergence of the seedling. • Post emergence: Rotting at the collar region of the seedling. • Crown rot: On the well-established plant, rotting at the basal portion and spreads
upward and leads to death of the entire plant. Management:
• Shallow sowing of the seeds and adopt wider spacing. • Spot soil drenching with copperoxychloride.
• Mosaic mottling of the leaves with alternate dark green and light patches. • Stunting of the plant. • Bushy appearance due to the proliferation of the auxillary buds.
Management: • Destruction of the infected plants and foliar spray with systemic insecticide.
Symptom: • Formation of the phylloid flowers. • All the floral parts are converted into green leaf like structure.
Management: • Foliar spray with tetracycline – 100ppm. • Foliar spray with systemic insecticides from two-leaf stage.
SUNFLOWER 1. Head rot: Rhizopus nigricans Symptom:
• Irregular water soaked lesion is seen on the backside of the head portion. • Lesion turns to black and spread to entire head and leads to rotting of the head.
Management: • Foliar spray with mancozeb -0.25%, calixin -0.1%
• Irregular water soaked lesion on the leaves. • Later it turns to black color and it spreads to petiole and stem.
Management: • Foliar spray with fosetyl aluminium -0.1%
COCONUT 1.Basal stem end rot: Ganoderma lucidum Symptom:
• Reddish brown oozing from the base of the stem and spreads upward. • Drooping of the lower fronds. • Oozing is through the cracks. • Formation of sexual fruiting body – basidiocarp.
5.Bud rot of coconut: Phytophthora palmivora Symptom:
• Pale yellow discoloration of the heartleaf. Withering of the heartleaf. • Infected leaves can be easily pulled out. • At the base of the fronds reddish brown rotting is seen.
Management: • Foliar spray and trunk injection with fosetyl aluminium – 0.1%
6.Grey blight : Pestalotia palmarum Symptom:
• Irregular/ circular shaped lesions with brown margin and grey centre. Management:
• Foliar spray with copper oxychloride. • Trunk injection with calixin.
7.Lethal yellowing: Phytoplasma Symptom:
• Stunting and yellowing of the plant. • Reduction of leaf size.
Management: • Destruction of the infected plants and foliar spray with systemic insecticide.
• Pre emergence: before the emergence of the seedling. Death of the sets occurs inside the soil itself.
• Post emergence: after the establishment of the seedling. Reddish brown lesion at the collar region of the seedlings is seen.
Management: • Spot soil drenching with copperoxychloride -0.25%.
2. Redroot of sugarcane: Colletotrichum falcatum Symptom: • Shrinkage of the cane. • Yellowing and drying of leaves in patches. • Reddish brown discoloration interrupted with white patches of fungal growth.
• On the leaves reddening of midrib is also seen. Management:
• Set treatment with carbendazim -0.1% • Foliar spray with tridemorph – 0.1%
3. Wilt: Cephalosporium sacchari Symptom:
• Stunting, yellowing of crown leaves. • Midrib of the leaves turn yellow white leaf lamina remains green. • Reddening of internal tissues without any white patches. • Infected canes emit foul smell.
Management: • Set treatment with carbendazim -0.1% • Foliar spray with tridemorph – 0.1%
4. Set rot/ pineapple disease: Ceratocystis paradoxa Symptom:
• Reddening of internal tissues without any white patches. • Infected cane emits pineapple odour. • Internodes become hollow and black in color.
Management: • Set treatment with carbendazim -0.1% • Soil drenching with coc-0.25%
5. Whip smut: Ustilago scitaminea Symptom:
• Severe infection is seen in ratoon crop. • Central shoot is converted into single whip like smut spores.
Management: • Foliar spray with carboxin/oxycrboxin -0.1%
• On the leaves tiger stripe symptom is seen. Veins turn brown and interveinal areas become chlorotic.
• Cupping of leaf and tissues b/w the veins dry in patches. Management:
• Spot soil drenching with copperoxychloride -0.25%
3. Black arm of cotton: Xanthomonas axonopodis pv.malvacearum Symptom:
• Seedling blight: Watersoaked lesions on the cotyledon leaves. • Angular leaf spot: On mature plants, water soaked spots on the leaves restricted in b/w
the vein and veinlets. • Vein blight: Angular spots in leaf lamina extend to the vein and veinlets. The vein and
veinlets become black and blighted. • Black arm: Blackening extends from veins to the sympodial branches leaving the plant
as bare resembles like black arm. • Boll rot: On the boll depressed, circular, reddish brown lesion is seen.
Management: • Spot soil drenching with copperoxychloride -0.25%. • Foliar spray with streptomycin sulphate- 200pm.
1. Panama disease – Fusarium oxysporumf.sp. cubense
- Symptoms appears only after 6 months of transplanting - Spliting of pseudostem @ the base near soil level - Cross section of the corm shows – vascular discolouration (Reddish brown streak around
the periphery of center of the corm - If we split open the infected rootlets – pinkish discolouration is seen due to nematode -
Management - Pairing &prolinage before plant for elimation of nematode damage - Sprinkle wthcarbofuran @20g/corm on surface before planting - Corm injection – with 2% carbendazim – 3ml / corm @ 6th and 7th month - Capsule application with carbendazim
- Spindle shaped lesions characterized by dark brown margin & grayish centre - It is surrounded by yellow halo and later they coalesce and cause drying
- Yellow streaks is seen in the centre of the corm with bacterial oozing - If we cut immature fruit – Blackening of the pulp is seen
6. Tip over disease / Erwinia rot – Erwinia caratovora Symptoms
- In both nursery and main field drying and wilting of plants is seen - At the base of the pseudostem rotting is seen - By giving slight pressure pseudostem will fall leaving corm inside
7. Bunchy top disease – Banana bunchy top virus (Vector: Pentalonianigronervosa) Symptoms
- Stunting of plants, bunching of terminal leaves gives resette appearance - Dark green streaks on petiole, midrib and leaf lamina - Green leaf like structure is seen at the tip of bract
On leaves: Small yellowish spots on leaves – spots swell and raised above the surface as brown corky outgrowth of spongy eruption – spots surrounded by yellow halo. On twigs: irregular raised cankers on the surface resulting in drying On fruits: round to irregular raised cankerous growth on the surface.
- Reduced foliage with severe die back of twigs - Fruits fails to ripen and remain green imparts unpleasant flavour to juice
7. Tristeza – Citrus tristeza virus Symptoms
- Vein flecking seen on leaves - Severe stem pitting is seen - Die back of entire tree
8. Exocortis – Citrus exocortis viroid
9. Fruit rots i. Blue & Green mould – Penicillium spp ii. Alternaria rot – Alternaria citri iii. Soft rot – Aspergillus niger iv. Sour rot – Geotrichumcandidum
- Fruits – Depressed, circular, brown spot on fruit surface resembling bird’s eye with grey centre
- Laves – Dark brown spot with grey centre surrounded by yellow halo - Stem – Black elliptical sunken lesions on young shoots cause girdling & death
4. Fruit rot i. Grey mould – Botrytis cinerea ii. Blue mould – Penicillium digitatum iii. Soft rot – Phomopsis viticola iv. Stalk end rot – Aspergillus niger v. Penicillium rot – Penicillium canescens vi. Rhizopus rot – Rhizopus nigricans
5. Fan leaf – Grapevine fan leaf virus (Vector: Xiphinema index) 6. Leaf roll – Grapevine leaf roll associated virus (Vector: Mealy bug)
- All parts of tree are affected. Small grayish or white patches of fungal growth appear. - Affected leaves become crinkled, curled and the entire surface of leaf is covered with
fungus. - On fruits causes depression andaffected fruits harden and develop cracks.
3. Fire blight – Erwinia amylovora Symptoms
- Infected flowers, leaves and twigs become water soaked, shrivel, turn brown to blackish and fall or remain hanging in the tree.
- Infected fruits mummified and finally turn black and clinging to tree
4. Crown gall – Agrobacterium tumefaciens Symptoms
- Hard and corky galls appear on the stem and roots at the crown region and infected plants are stunted and chlorotic.
VEGETABLES TOMATO
1. Damping off – Pythium aphanidermatum • Seedlings are affected. • Brown discolouration at the lower portion of stem.
2. Early blight – Alternaria solani • Symptoms are observed on leaves, stem and fruits. • Brown, necrotic and irregular with concentric zones on leaf • On stem brown discoloration leads to girdling.
5. Spotted wilt – Tomato spotted wilt virus - Thrips • Necrotic irregular spots are visible on the surface of leaf with green centre. • Leaf exhibits bronzing. • On fruit, pale yellow patches are scattered on the surface.
CHILLIES 1. Damping off – Pythium aphanidermatum 2. Die back and fruit rot - Colletotrichum capsici
• Symptoms are seen on stem and fruit – stem shows die back symptoms. • Water soaked spots are seen on mature fruits - Affected portion turns white. • Acervuli are formed on the spots and seen as black dots in large numbers.
• Depression on the upper surface of leaf • Bulging on lower surface covered with myceial growth • On stem – Blisters are seen showing craking symptoms
Fruit & vegetables – 20-30% Food grains – 9.3% Post Harvest disease occurs in transit and storage are mainly due to the activity of fungi,
bacteria and of non-parasitic origin.
Effects of storage fungi on grains 1. Decrease the germination 2. Reduce the quality of grains 3. Cause discoloration of seeds 4. Produce toxins in stored grains 5. Cause biochemical changes and damage seeds 6. Cause heating and affect quality
Aflatoxin produced by Aspergillus flavus in groundnut, which is highly toxic. Heating favours growth of storage fungi. At higher temperature (45oC) grains get killed.
A. A. flavus & A. glaucus - 45oC B. Mucor - 30oC C. Fusarium - 35oC D. Alternaria - 25oC
Fungus require Moisture content of about Aspergillus flavus – 17.5 – 18%
Management • Harvest and store the crops at optimum moisture content 12-13% and temperature
12-15oC • Fumigate the storage godowns • Provide proper ventilation to storage godowns
Disease of vegetables and fruits Infection may occurs before harvesting, during post harvest handling or storage. Ripened fruits are infected easily, while green fruits show resistance. Reasons are,
1. Nutritional requirement of fungus is not met out b the fungus 2. Higher enzyme potential is needed to invade green fruits 3. Phenolics and some other toxins present in the green fruits 4. Energy requirement of fungus is met out in ripening stage of fruit only.
Causal organism Biotic factors Soft rot producing bacteria, Fungus due to predisposing factors such as humidity, temperature, presence of bruises or lesions on fruits and vegetables
Abiotic factors When fruits and vegetables stored in poor ventilated conditions such s High level of CO2, Low O2 post harvest disease may happen.
Black heart of apple and Potato – caused by lack of oxygen (High temp, poor ventilation)
Crop Fungus Damage
Paddy Trichoconis pudwickii Black discoloration of grains
Drechlera oryzae Alternaria alternata Fusarium moniliforme Aspergillus niger, A. flavus Penici l l ium chrysogenum, Mucor, Rhizopus sp
Brittleness of grain
Wheat Anguina tritici (Nematode) Produce galls in seeds
Sorghum Fusarium moniliforme Grains converted in to smuts
Groundnut Aspergillus flavus, A. candidud, A. repens, A. restrictus
BIOLOGICAL CONTROL Biological control - reduction of inoculum density or disease producing activities of a Pathogen by introduction of one or more antagonists. Biological control is nothing but control of plant diseases using living microorganisms. The four main mechanisms involved in the biocontrol are
(i) Parasitism - antagonist parasite the other organism, (ii) Antibiosis - antagonist may secrete harmful metabolites (iii) Competition - antagonist may compete with the pathogens for nutrients or space (iv) Lysis - may cause death of the parasite by producing enzymes