A Perspective on Integrated Disease Management … DR ABHAY PANDEY A...or more than one concepts of plant disease management. Use of such integrated approach in plant disease management

Bio Bulletin (2016), Vol. 2(2): 13-29, Pandey, Sain and Singh 13

ISSN NO. (Print): 2454-7913ISSN NO. (Online): 2454-7921

A Perspective on Integrated Disease Management in AgricultureAbhay K. Pandey*, Satish K. Sain** and Pooja Singh***

*Plant Health Management Division, National Institute of Plant Health Management,Rajendranagar, Hyderabad-500030 TS, India.

**ICAR- Central Institute for Cotton Research, Regional Station Sirsa, 125055 Haryana, India***Bacteriology and Natural Pesticide Laboratory, Department of Botany, DDU Gorakhpur University

Gorakhpur, Gorakhpur-273009 UP, India.

(Corresponding author: Abhay K. Pandey, [email protected])(Published by Research Trend, Website: www.biobulletin.com)

(Received 19May 2016; Accepted 22July 2016)

ABSTRACT: In this review we have described the history, biotic and abiotic stress of plantdisease, types of plant disease, and its integrated management. The history of plant diseasemanagement is showing the traditional, chemical and integrated approach for the plant diseasemanagement. The abiotic means environmental factors while biotic includes microbes,phanerogamic plants, viruses, nematodes etc. These abiotic and biotic factors cause severaldiseases in plants like necrotic symptoms, abnormal growth and development of plant tissues,gummosis, wilting, rust, mildews etc. A number of factors responsible for the transmission ofthese diseases, they are described under this chapter. Besides, disease triangle and disease cycleare also described. Furthermore, disease diagnostic procedure has been given in fragment ofsample collection method, sample submission method etc. Integrated disease management hasbeen described here which comprises cultural, physical, mechanical, genetic, biological andchemical. Institutional, sociological, economic and political constraints in integrated diseasemanagement are also mentioned.

Key Words: Plant Diseases, Cultural practices, Physical and Mechanical practices, Biological control,Chemical control

INTRODUCTION

Any biotic or abiotic agents, which induce thedisease in plant, are referred as the cause ofdiseases. Organisms that cause infectious diseaseinclude fungi, bacteria, viruses, viroids, virus likeorganisms, phytoplasmas, protozoa, nematodesand parasitic plants and environmental conditionssuch as lack or excess of nutrients, moisture, light,etc. to presence of toxic chemicals in Air or soil.Plant disease can be defined as “a series ofharmful physiological processes caused bycontinuous irritation of the plant by a primaryagent” or “physiological or structural dis-balance inplant caused by certain external agencies.

However, the definition which is accepted byAmerican Phytopathological Society and theBritish Mycological Society states that “Disease isa malfunctioning process that is caused bycontinuous irritation which results in somesuffering-producing symptoms”. Therefore, theplant disease is a structural abnormality orphysiological disorder or both due to an organismor unfavorable conditions that may affect the plantor its parts or products or may reduce theireconomic value. Integrated Disease Management(IDM) is a concept derived from the successfulIntegrated Pest Management (IPM) systems whichconsists of scouting with timely application of a

Bio Bulletin 2(2): 13-29(2016)(Published by Research Trend, Website: www.biobulletin.com)

mailto:[email protected]

www.biobulletin.com


combination of strategies and tactics. These mayinclude site selection and preparation, utilizingresistant cultivars, altering planting practices,modifying the environment by drainage, irrigation,pruning, thinning, shading, etc., and applyingpesticides, if necessary. But in addition to thesetraditional measures, monitoring environmentalfactors (temperature, moisture, soil pH, nutrients,etc.), disease forecasting, and establishingeconomic thresholds are important to themanagement scheme. These measures should beapplied in a coordinated integrated andharmonized manner to maximize the benefits ofeach component. The main goal if IDM are:

-Eliminate or reduce inoculum-Reduce the effectiveness of initial inoculum-Increase resistance within the host-Delay the onset of disease-Slow the secondary cycles-Uses several methods in which routine useprovides disease control

IMPORTANCE OF THE PLANT DISEASE

Plant disease sometimes spread as epiphytoticsand destroy the crops growing in the very largeareas. They damage the crop growing in the fieldas well as stored products in the storage. Thedisease can occur any time and at any stage ofthe plant growth from the time of sowing of seedsto the storage of the products and cause a greateconomic loss. In Asia alone, the food grainsamounting millions of dollars are being destroyedevery year due to crop diseases. One such case,which is often quoted in the plant disease historyis an example of famine caused due to plantdisease. Such diseases include late blight ofpotato by fungus Phytophthora infestans in Ireland(1847), coffee rust by Hemileia vastatrix inSrilanka (1870), sigatoka leaf spot disease ofbanana by Mycosphaerella musicola in Centraland South America (1930). In India, the famousBengal famine in 1942 was due to leaf spotdisease of rice caused by Helminthosporiumoryzae and approximately two million people diedof starvation. Due to impact of plant disease andeconomic losses caused by them, the science ofplant pathology is attracting interest of all most allthe countries of the world.

A. Milestone in Disease ManagementFarmers have been at the mercy of plant diseasessince plants were first domesticated. Themysterious appearance of blights and mildews,apparently coming from nowhere, led to theoriesof gods, vapors, demons, and decay as causes ofdisease. Beginning in the early 1800s, plant

scientists and chemists began the long journey todiscover and invent fungicides that would reducedisease losses. In 200, Cato mentioned thefumigation of trees with bitumen and sulphur.Prevost (France) (1807) recommended coppersulphate for wheat seed treatment against buntand demonstrated first time the fungitoxic value ofcopper compounds. During 1821-1851 sulfur wasemerge as effective fungicide for the control ofpowdery mildew disease. Millardet (French) (1882)discovered Bordeaux mixture to control downymildew of grapevine. Bewley (1921) developedchestnut compound to control damping –offdisease as a soil drench in nursery beds. Sanford(1926) conducted first experiment on biologicalcontrol of plant pathogens with antagonistic(Bacillus subtilis) in Canada. In 1932, Weindlingsuggested use of Trichoderma spp. as biocontrolagent. Waksman and Schatz (1943) discoveredfirst broad spectrum antibiotic streptomycin.During 1952-1978 fungicidal properties of firstheterocyclic nitrogen compound captan, systemicfungicide Oxanthin, benomyl (against powderymildew fungus of cucurbits), metalaxyl (againstoomycetes) and fosetyl-Al (against phycomycetes)were investigated. In 1996 first strobilurinsfungicide launched which was isolated from woodrotting mushroom fungi.

B. Scope of Integrated Disease ManagementSeveral synthetic fungicides have been used forthe management of diseases of commerciallyimportant agricultural crops. However, theircontinuous use in agriculture system causesseveral side effects in agro-ecosystem as well asin consumer’s health. Numerous health andenvironmental reasons to use non-toxicalternatives to pesticides exist. Use of integrateddisease management strategies can be certainlyan answer to these problems. The principles ofplant disease management should always bebased on the integration of basic concepts such asavoidance, exclusion, eradication, protection,resistance and therapy. Adoption of IntegratedDisease Management against the diseasesencountered in crops is of utmost importancebecause dependency on chemicals for themanagement of various diseases is a great healthhazard to the consumer. This assumes greaterimportance in the developing countries where thefarmers are not educated enough to follow somecutoff date for application of chemicals to thestanding crops. All these factors along with thegrowing awareness among the users regardingfungicides residues, pollution to the environmentand sub-soil water and increased problem of

www.biobulletin.com


pathogen resistance towards the fungicides, havebeen the compelling reasons for moving awayfrom the total dependence upon the fungicidesand to adopt IDM strategies that would involve oneor more than one concepts of plant diseasemanagement. Use of such integrated approach inplant disease management is cost effective,renewable, eco-friendly and non-toxic to the plantsas well as non-target organisms.

HISTORY OF PLANT DISEASE MANAGEMENT

A century ago the science of plant pathology wasjust being born and L. R. Jones wondered, at ameeting in Atlanta in 1913, whether it was a goodthing to separate plant pathology as a disciplinefrom botany. This was only a few decades afterthe idea that fungi were causal agents of plantdiseases had been accepted and that the conceptof "spontaneous generation," which regarded fungias symptoms on plants suffering from badenvironmental conditions, had been on its way out.This new concept of germs being causal agents ofdisease had its earliest supporters among plantpathologists like Tillet for bunt in 1755, Prevost forsmut in 1807, Berkeley and de Bary for the lateblight fungus of potatoes in the 1850s.Unfortunately, the broader significance of thesefindings was not recognized, and it was only in the1860s that the work of Pasteur and Koch onhuman pathogens led to the breakthrough of thegerm theory. Therefore, it is not surprising that theunderstanding and the standard of fungicides acentury ago was very rudimentary. The history ofdisease management thus has three distinctphases, viz., the era of traditional approaches, theera of fungicides/bactericides and the era of IDM.

A. Era of traditional approachesAbout the time humans started aggregating intovillages and began planting selected food crops inclusters near rivers in fertile valleys, pests becamean increasing challenge. Through trial and error,humans began to learn how to improve conditionsand control the environment. People learned toperform cultural and physical control practices forcrop protection. Methods such as flooding,destroying or using crop refuse, roughing diseasedplants, tillage to expose and eliminate soil bornepathogens, removal of alternate hosts ofpathogens and insects, timing of planting, croprotation, trap crops, determining optimum plantingsites, pruning, dusting with sulphur, and othersreduced damage potential to many crops frommany pests. This was followed by the use of plantproducts from neem, chrysanthemum, rotenone,tobacco and several other lesser known plants in

different part of the world. These cultural andphysical control methods are still viable today.

B. Era of fungicidesAs with many inventions, "development" of the firstfungicide was the result of good observations. Thefirst use of brining of grain with salt water followedby liming took place in the middle of the 17thcentury to control bunt, and followed theobservation that seed wheat salvaged from thesea was free of bunt. Up until the 1940s chemicaldisease control relied upon inorganic chemicalpreparations, frequently prepared by the user. Themajor products used for the disease managementare given in the Table 1.

Table 1: Fungicides in use up until 1940.

From 1940 to 1970 there were a number of newchemistry classes introduced as fungicides. Thedecade from 1960 to 1970 the most widely usedprotectant fungicides, mancozeb andchlorothalonil, were introduced. The decade alsogave us the first broad-spectrum foliar systemic,thiabendazole, and the systemic seed treatmentcarboxin. The first case of resistance tobenzimidazoles occurred in powdery mildew ingreenhouses in 1969, one year after introduction.During the 1980s fenpropidin and fenpropimorphwere key fungicides in the European cerealmarket, while tridemorph was used extensively forsigatoka followed by the seed treatment carboxin(Vitavax), which is highly effective on bunts, smutsand assorted Basidiomycetes such as Rhizoctoniaspp.The intensive and extensive use, misuse andabuse of synthetic fungicides during the ensuingdecades caused widespread damage to theenvironment. Additionally, disease problems insome crops increased following the continuousapplication of fungicides. This, in turn, furtherincreased the consumption of fungicide resulting inthe phenomenon of the fungicide treadmill. The




















combined impact of all these problems togetherwith the rising cost of pesticides provided thenecessary feedback for limiting the use ofchemical control strategy and led to thedevelopment of the IDM concept.

C. Era of IDMThe IDM terms came from integrated pestmanagement (IPM).In the late 1960's, a movementto develop more environmentally benign cropprotection methods began. Although economicswas the prime driver to use crop scouting todetermine spray schedules, it was a first real steptoward an IPM approach. IDM calls for minimaluse of pesticides, and only if deemed necessary.IDM gives preference to other control methodssuch as host-plant resistance, cultural practicesand biological control. In the 21st century, the termof "agricultural sustainability" has become a normfor modern agriculture and numerous non-chemical methods for control of crop diseasessuch as pathogen-free seeds, disease resistance,crop rotation, plant extracts, organic amendmentsand biological control are considered less harmfulthan synthetic chemical pesticides and, therefore,offer great potential for application in conventionalagriculture, organic farming and/or soilless culture.No single method can provide satisfactory controlof crop diseases. Integration of all effective andeco-friendly measures in accordance with thedynamics of the agroecosystem managementwould be the best strategy for efficient control ofdiseases in crops.

CONCEPT OF PLANT DISEASE

The Greek philosopher Theophrastus (300, B.C)was the first to study and write about diseases oftrees, cereals and legumes. He believed that godcontrolled the weather that brought diseases.Plant diseases were a manifestation of the worthof God. It is due to religious belief, superstitions orit is the effect of star moon and bad wind. E.g.Romans actually created a special rust God calledRobigo for rust diseases of grain crops. Theyoffered sacrifice of red dogs and sheep. Afterinvention of compound microscope in the mid1600 scientist enable to see many microorganismsassociated with diseased plants and they come tobelieve that the mildews, rust, and othersymptoms observed on plants andmicroorganisms found on diseased plant. LouisPasteur (1860-63) provided irrefutable evidencethat microorganisms arises only from pre-existingmicroorganisms and fermentation is a biologicalphenomenon not just a chemical one. It isaccepted that a plant is healthy or normal when it

can carry out its physiological functions to the bestof its genetic potentials. The pathogen may causedisease in plant by:

-Weakening the host by continuously absorbingfood from the host cells for their own use.

-Killing or disturbing metabolism of host cellsthrough toxins enzymes or growth regulatingsubstances, they secrete.

-Blocking the transportation of food, mineral,nutrients and water through the conductivetissues.

-Consuming the contents of the host cells uponcontact.

A. Disease triangleThe interactions of the three components such ashost, environment (physical viz., climatic, soil andtopographical and biotic) and pathogen of diseasehave been visualized as a triangle generallyreferred to as the “disease triangle”. Each side ofthe triangle represents one of the threecomponents (Fig. 1). The length of each side isproportional to the sum total of the characteristicsof each components that favour disease i.e. if thehost is resistant, matured and widely spaced, thehost side and amount of disease would be small orzero, whereas if the host or plants are susceptible,at susceptible stage of growth or densely planted,the host side would be long and the amount ofdisease could be great. Similarly, the virulent,abundant and active the pathogen, the longer thepathogen side and greater is the amount ofdisease. Also more favourable the environmentalconditions (e.g. temperature, moisture and wind)help the pathogen or that reduces the hostresistance, longer will be the environmental sideand greater will be the amount of disease. Whenthese three components of the disease triangleare quantified, the area of the area of the trianglerepresents amount of disease in a plant or in aplant population. If any of the three components iszero, there can be no disease.

Fig. 1.Disease Triangle.

B. Mode of disease transmission


Transport of spores or infectious bodies, acting asinoculum, from one host to another host at variousdistances resulting in the spread of disease, iscalled transmission or dissemination or dispersalof plant pathogens. There are 2 major types oftransmission of plant pathogens i.e. direct andindirect transmission.

Direct transmission: Disease transmission,where the pathogen is carried externally orinternally on the seeds or planting materials likecuttings, sets, tubers, bulbs, etc. It may be(a) Germinative transmission, where plantpathogens are transmitted by seeds or propagulesof host plants, e.g. loose smut of wheat, loosesmut of barley, leaf blight of wheat and TMV etc.(b) In vegetative transmission pathogens aretransmitted through tubers, bulbs, rhizomes,cuttings, graft, e.g. ring and brown rot of potato,late blight of whip smut red rot of sugarcane etc.(c) In adherent transmission the propagules ofthe pathogens are carried over the surface of theseeds or vegitatively propagated parts e.g. Bunt ofwheat, covered smut of barley, ergot of rye andbajra, wart disease of potato etc.

Indirect transmission: The pathogen spreadingitself by way of its persistent growth or certainstructures of the pathogen carried independentlyby natural agencies like wind, water, animals,insects, mites, nematodes, birds, etc. are thedifferent methods of indirect transmissions.(a) Autonomous transmission. Some root rottingfungi infecting certain seasonal crops also aretransmitted by this method. Wood rotting fungisuch as Armillaria, Fomes, Polyporus etc. migratefrom plant to plant through soil. Others include rootrot of cotton and wilt disease caused byPhymatotrichum omnivorum and Fusarium sp. etc.(b) Wind dispersal: Pathogens causing powdery,downy mildews, leaf spots, blasts, blights and rustdiseases are transmitted through wind.(c) Water dissemination: Certain soil inhabitingpathogenic fungi and bacteria causing root andcollar rots, wilts, foot, rots, etc. are likely to betransmitted to much longer distances through theagencies like irrigation water, streams and rivers,etc.(d) Transmission by insects, mites andnematodes: Most of the viral diseases of plantsare transmitted through the agency of differentinsects (Fig. 2). Both types of insects viz., suckingand chewing or/biting are capable of transmittingviral diseases. Insects in such cases are called the`vectors’ for the particular viral pathogen.

The insects responsible for transmission of viraldiseases belong to the species of aphids, thrips,jassids (leaf hoppers), whiteflies, mealybugs, etc.Certain bacterial and several fungal pathogens arealso known to be carried by insects. Manybacterial diseases such as cucurbit wilt, black legof potato are transmitted by maggot and fire blightof apple is transmitted by bees. It is suspected thatsome viral diseases of chillies, tomato, brinjal andpigeon pea etc. have vector relationship withmites. Nematodes are soil borne organisms whichsometimes act as agent for dissemination ofbacterial, fungal and viral pathogens. For exampleyellow ear rot disease of wheat is transmitted by

ear cockle nematodes.

Fig. 2. Some insect vectors responsible fortransaction of plant disease.

(e) Biological transmission: Dodder, a higherflowering parasite is known to transmit certain viraldiseases which remain `persistent’ in the dodderplant.(f) Cattle and birds: Cattle while feeding oncontaminated fodder ingests the viable fungalpropagules into the intestine which pass out assuch in the dung and when such dung is used asmanure may be source of inoculum e.g. smutspore.(g) Human dispersal: While handling thediseased material and unknowingly and indirectlytransmit the pathogens to healthy seedlings orplant parts through his contaminated hands. Thisis a kind of `continuous’ mode of transmission.(h) Farm implements tools: The pathogens inthis case are usually carried in the form of bits ofplant disease debris lying in the soil. Similarly toolsused for carrying out operations like cutting,pruning, budding, grafting, thinning etc. also helpin the transmission of certain diseases from plantto plant. Several viral diseases are disseminatedthrough the budding and grafting operations.


C. Biotic and abiotic stressThere are so many agents which initiate thereactions in host plant causing diseases. Suchagents are called causal agents of the diseaseand are basically two types i.e. biotic and abiotic.Abiotic disorders are caused by nonliving factors,such as drought stress, sunscald, freeze injury,wind injury, chemical drift, nutrient deficiency, orimproper cultural practices, such as overwateringor planting too deep. Mango necrosis or black tipof mango is caused due to brick kiln fumescontaining SO2, coal gas and chlorine. Despite ofthese problems, excessive mineral or deficiency ofminerals are also responsible for major diseases.Some mineral deficiency symptoms includes redleaf of cotton (nitrogen), dwarfing of cotton(phosphorus), cotton rust and little spot of alfalfa(potassium), heart rot of beet, brown heart ofcabbage, internal cork of apple (boron), die backof citrus (copper), gray speck disease of oat(manganese), whiptail disease of cauliflower(molybdenum) and khaira disease of rice (zinc).Biotic plant problems are caused by livingorganisms, such as fungi, bacteria, viruses,nematodes, insects, mites, parasitic floweringplants and animals. Unfortunately, the damagecaused by these various living and nonlivingagents can appear very similar.

D. Parasitism and pathogenesisAn organism that lives on or in some otherorganism and obtains its food from the latter iscalled a parasite. Parasitism is the removal ofnutrients from a host by a parasite. There are twomajor types of parasitism: obligate and non-obligate.

-Obligate parasites are biotrophs depend onliving cells for their existence. This group includesrust and mildew fungi, viruses, viroids, mollicutes,fastidious bacteria, nematodes, protozoans, andparasitic plants.-Non-Obligate parasites can be biotrophic ornecrotrophic. Necrotrophic pathogens kill theirhost's cells in advance of colonization. Thenecrotrophs typically use enzymes and toxins tokill the cells they feed on.-Facultative saprophytes are parasites thattypically depend on living material, but can utilizenecrotic materials in situations where no livematerial is available. Facultative parasites livepredominately as saprophytes, but under specificconditions can parasitize living organisms.Pathogenicity is the ability or capacity to incitedisease. Relating to pathogenicity, the termsvirulence and aggressiveness are oftenused. Aggressiveness is the relative ability to

colonize and cause damage to plants. In short, it'swhether the pathogen causes a little or a lot ofdisease under standard conditions.Virulence is the degree of pathogenicity of a givenpathogen. Pathogenesis is the sequence ofprogress in disease development from the initialcontact between a pathogen and its host to thecompletion of disease symptoms. The event ofpathogenesis consisted of three steps i.e. pre-penetration, penetration and post penetration. Pre-penetration is the stage that includes theinteraction of host pathogen before entry ofpathogen into the host. Once a pathogen reachesa suitable infection site at the plant surface, it mustbreach a series of barriers to gain entry into itshost before establishing a parasitic relationshipduring the penetration stage. After successfulpenetration, the pathogen proceeds further toestablishment of proper infection. This stage iscalled invasion.After successful infection, the pathogen derives itsnourishment from the host, starts multiplicationand secretes some chemical substances toexpress the symptom of the disease. Thehaustoria absorb nutrients from the host andsupply it to the main body of pathogen. Thesepathogens soon start reproduction andmultiplication.

E. Disease cyclePlant disease cycles represent pathogen biologyas a series of interconnected stages ofdevelopment including dormancy, reproduction,dispersal, and pathogenesis. The progressionthrough these stages is determined by acontinuous sequence of interactions among host,pathogen, and environment. The main events ofstages comprising the disease cycle include thefollowing: production and dissemination of theprimary inoculum, primary infection, growth anddevelopment of the pathogen, secondary infection,and overwintering (Fig. 3).1. The primary inoculum is the part of the

pathogen (that is, bacterial or fungal spores orfungal mycelium) that overwinters (over-seasons) and causes the first infection of theseason, known as primary infection.

2. Dissemination refers to the spread or dispersalof the pathogen from an inoculum source to ahost. Dissemination can occur by wind,splashing rain, insects, infested pruning tools,infected or infested transplants, and othermeans.

3. Primary infection occurs when the pathogencomes into contact with a susceptible hostunder favorable environmental conditions. Most


fungal and bacterial pathogens require freewater for spore germination; consequently,infection is favored by prolonged warm, wetperiods with high relative humidity.

4. Growth and development of a pathogen usuallyoccurs on or within infected plant tissue. Fungigrow and spread within their host by means ofmycelium. Bacteria spread by rapidlyincreasing in numbers.

5. Secondary infection results from spores or cellsproduced following primary infection or fromother secondary infections. The secondaryinfection cycle can be repeated many timesduring the growing season. The number ofcycles is dependent on the biology of thepathogen and its host and the duration ofenvironmental conditions needed for infection.

6. Overwintering or over seasoning is the ability ofa pathogen to survive from one growing seasonto the next.

Fig. 3. Stage in disease cycle.

F. Causes and Identification of Plant Diseases:A plant disease is the resultant of close interactionbetween the host plant and the disease incitingagent. There are so many agents which initiate thereactions in host plants causing the diseases.Such agents are called cause of disease. Suchagents include living and non-living as well asviruses and have been described earlier.

Classification of plant disease: Plant diseasemay be classified in various ways on the basis ofcasual agencies, spread and severity of infection,their perpetuation and transmission, the part ofhost affected and symptoms produced by the hostplants.Classification based on causes of diseases:On the basis of causes of the diseases, they canbe divided into noninfectious and infectiousdisease.

a. Non-infectious diseases: Such types ofdiseases are not caused by living organisms andusually occur by lack of environmental conditions,nutritional deficiencies, and physiological disordersi.e. heat canker of flax caused by hightemperature, apple scald and black tip mangocaused by injurious atmosphere, whiptail diseaseof cauliflower caused by deficiency ofmolybdenum, tip rot or necrosis of mango fruitscaused due to boron deficiency etc.b. Infectious disease: Such diseases are causedby living organisms (bacteria, mycoplasmas, fungi,nematodes, algae, protozoans) and viruses andare parasitic in nature. These types of diseasesshow presence of sign and can be easilytransmitted form diseased plants to healthy plantsthus, are infectious in nature.

Classification based on spread and severity ofinfection: On the basis of geographicaldistribution and severity of infection, plantdiseases are classified into following categoriesi.e. endemic, epidemic, sporadic, etc. on the samelines of insect pests.

Classification based on the part of hostinfected: On this basis disease may be localisedor systemic. In localised infection, diseaseoccurs in a particular part or organ of the hostplant. Such types of example include root disease,stem disease, foliage disease, spike disease,depending upon the organ infected. In systemicinfection the disease spread throughout the plantbody.

Classification based on perpetuation anddispersal of diseases: On this basis, diseasesare categorized into following parts.a. Soil borne diseases: Inoculum of the diseasescausing pathogen remains in soil and penetratethe plant resulting in diseased condition e.g. rootrot, wilt.b. Seed borne diseases: The micro-organismsare carried along with seeds and cause diseaseswhen congenial condition occurs e.g. Alternarialeaf spot.c. Air borne diseases: The micro-organisms arespread through air and attack the plants causingdiseases e.g. blight, rust, and powdery mildew.d. Water borne disease: This category of plantdisease includes those in which primary inoculumis perpetuated and transmitted through water e.g.blight of paddy.e. Diseases spread by insects: The viraldiseases are spread by insects. The insects whichcarry the viruses are known as vectors.


Classification based on diseases symptoms:Such categories include smut, anthracnose,canker, mosaic, powdery and downy mildewdamping off, rots, gall etc.Symptoms of plant diseases: The symptoms areexternal or internal expressions of a plant thatindicate that it is suffering from. Generalizedsymptoms may be classified as local or systemic,primary or secondary, and microscopic ormacroscopic. Local symptoms are physiological orstructural changes within a limited area of hosttissue, such as leaf spots, galls, andcankers. Systemic symptoms are those involvingthe reaction of a greater part or all of the plant,such as wilting, yellowing, and dwarfing. Ingeneral, the kinds of systems produced by specificgroups of casual organisms can be listed asfollows:Symptoms caused by fungi: Fungi and fungi likeorganisms (FLOs) such asPythium and Phytophthora collectively cause morediseases in the plants then do rest of the pathogenas a whole. These symptoms can be broadlycategorized as following depending upon theprocesses involved in the appearance of diseasesymptoms on the host.a. Necrotic symptomsb. Abnormal growth and development of planttissuesc. Other symptomsa. Necrotic Symptoms: These symptoms involvethe death and destruction of plant tissues resultingin brittle appearance of the tissue.1. Leaf spot: Localized lesions produced on theleaves of the host plants as a result of pathogeninfection (Fig. 4 A).Examples: Alternaria sp.,Cercospora sp., and Pyllachora sp. spots the deadtissue of the spot is shed leaving a circular hole,called shot hole e.g. etc. (Fig. 4 B).2. Blight: Blights are the general and rapiddestruction of the growing succulent tissues likeleaves, shoots, twigs and blossom. For e.g.,Phytophthora sp., Cryophonectriaparasitica, Ascochyta sp. (Fig. 4 C).3. Blast: Necrotic lesions are visible on theleaves, nodes, and at the base of heads resultedto rapid browning and death of the tissue.Example: Rice blast by Pyricularia oryzae (Fig. 4D).4. Cankers: The localized necrotic lesions aresunken and surrounded by successive layers ofcork cells. For eg.: Phytophthora sp., Nectaria sp.(Fig. 4 E).5. Scab: These are the localized lesions which aredue to the slightly raised and cracked outer layerof the fruits, leaves or tubers etc. The cracked

tissue becomes dry and corky. Example: applescab by Venturia inaequalis (Fig. 4 F).6. Anthracnose: It is a type of disease in whichdark necrotic, sunken lesions are produced onmainly leaves, fruits and stem. Example: Elsinoeveneta on raspberry and Colletotrichum spp.cause anthracnose of cotton (Fig. 4 G).

Fig. 4. Symptoms of fungal diseases. A. Leafspot, B. Shot holes, C. blight, D. Blast, E. Canker,

F. Scab, G. Anthracnose, H. Blotch, I. Dieback.

7. Blotch: These are usually large, irregularshaped spots on the surface of the plant leaves,stem or flowers. At initially spots appear purplish,circular on upper surface and later on lower andlater become glossy dark purple and then beown.Example: Septoria tritici blotch of wheatand Cladosporium leaf blotch of peony (Fig. 4 H).8. Dieback: It is the progressive and extensivedeath of the shoots and roots that starts from thetip of the shoots. Example: Lasiodiplodiatheobromae cause dieback of mango (Fig. 4 I).9. Damping off: The young or seedlings collapseat the back due to pathogen attack before or afterthe germination.Example: Pythium sp., Phytophthora sp., Rhizoctonia solani (Fig. 5 B).10.Basal stem rot: The pathogen destruct thecambium and vascular tissue hence the plantshows typical symptoms of wilting.Example: Ganoderma zonatum cause basal stemrot in palms (Fig. 5C).11. Root rot: The disintegration and decay of thetissues of roots by various fungal pathogens.Example: Phymatotrichum omnivorum cause rootrot of cotton (Fig. 5D).12. Soft and dry rot: Wet rots are caused bycertain fungi which caused by disintegration of thetissues in leaves, fruits, wood, tubers etc.Example: Rhizopus spp. cause soft rot of sweetpotato (Fig. 5E).


b. Abnormal growth and development of planttissues: These symptoms results due tothe hypertrophy (increased cell size)and hyperplasia (increased number of cells) due tothe interaction of chemicals produced by thepathogen and the tissues of host. The tissuesshow abnormal growth pattern which result inaltered morphology and physiological functioningof the affected part or entire plant.

Fig. 5. Symptoms of fungal diseases. A. Decline,B. Damping off, C. Basal stem rot, D. Root rot, E.

Soft rot, F. Galls, G. Club root, H. Wart, I. Powderyscab.

1. Galls: Abnormal growths (swollen/raisedtissues) formed by the interaction of the certainfungi on the host leaves, stems, roots or flowers.Example: Dibotryon morbosum causes "poop gall"of choke cherry (Fig. 5F).2. Club-root: Gall formation or distortion takeplace in the roots giving the appearance of spindleor clubs.Example: Plasmodiophora brassicae cause clubroot of crucifers (Fig. 5G).3. Warts: Hard, benign protuberances(called warty excrescences) produced on thestems or tubers and caused by fungal or viralpathogen. Example: Synchytriumendobioticum cause potato wart disease (Fig. 5H).4. Powdery scab: The infected tissue has brownspongy spots, which are dry and in severeconditions give appearance of warts.Example: Sponiophora subterranean causespowdery scab of potato (Fig. 5I).5. Witchs’ broom: Profuse branching of the twigstakes place in which the new twigs are turnedupward, short, and bear small leaves giving theappearance of witches’ broom. Example:Moniliophthora perniciosa cause witches' broomdisease (WBD) in cocoa (Fig. 6A).

6. Leaf curling: Easily distinguishable symptomslike distortion, discoloration and curling of theleaves due to fungal pathogen (Taphrinadeformans). In the early stages the leaves showred colouration, thicker and softer than normalmature leaves (Fig. 6B).

Fig. 6. Symptoms of fungal diseases. A. Witchesbroom, B. Leaf curl, C. Gummosis, D. Wilt, E.

Rust, F. White rust, G. Smut, H. Downy mildew, I.Ergot.

7. Atropy: It is the reduction in size due to theparasitic fungi which induce hypertrophy and thegrowth is said to be suppressed.Example: Peranospora brassicae suppresses thefloral buds in Brassica sp.

c. Other Symptoms:1. Gummosis: It is the oozing out (seeping) of theamber coloured exudate from the diseased tissuewhich may be bark of the stem, leaves or fruitsand later sets into solid mass. Different species ofBotryosphaeria cause gummosis in different plants(Fig. 6C).2. Leaf dropping and fruit drooping: Dropping ofleaves or fruits is also very common symptomassociated with infection of any fungal pathogen.Example: Phytophthora attack onpalm, Cercospora and Hemileia.3. Wilt/Vascular wilt: Vascular bundle is blockedout by the pathogen and results in the loss inturgidity and drooping of the leaves and shoots ofthe plant leading to permanent wilting. Mostcommon vascular wilts are causedby Fusarium and Verticillium (Fig. 6D).4. Rust: Rusty appearance on the leaves andstems of the host plant as a result of the infection,produced by the fungal pathogen belonging to theorder Uredinales (rust fungi) (Fig. 6E).


5. White rust: White coloured spots of conidiaspores of oomycete Albugo candida in brassicafamily (Fig. 6F).6. Smuts: It is a disease characterized by massesof dark, powdery spores of smut fungi belonging toorder Ustilaginales (Fig. 6G).7. Mildews: Presence of whitish mycelium andfructification covering the areas on leaves stemsor fruits. In Powdery mildew mycelium is on theupper surface while in Downy mildew it presenton the lower surface. Example: Bremia,Peranospora, Plasmopara,and Pseudoperanospora cause downy mildews ofdicotyledonous plants such as lettuce, tobacco,grapes and cucurbits. Peronoslerospora,Sclerophthora and Sclerospora cause downymildews of monocots such as corn, sorghum andsugarcane (Fig. 6H).8. Ergot: The grains in the heads of the cerealsare replaced by black or purple colour edsclerotiaof ergot fungus Claviceps purpurea, just before theharvest (Fig. 6 I).

Symptoms caused by bacteria: Bacterialdiseases in plants may affect stems, leaves orroots or be carried internally. Some examples ofcommon bacterial diseases of vegetable crops areprovided in the Fig. 7.

Fig. 7.Symptoms of bacterial diseases. A. Blackrot, B. Scab/bacterial canker, C. Bacterial soft rot,D. Bacterial leaf spot, E. Bacterial wilt, F. Bacterialblight, G. Bacterial speck, H. Bacterial brown spot,I. Tumors and Galls.

1. Black rot: Light-brown to yellow V-shapedlesions on the leaf, this becomes brittle and drywith age. Vein blackening occurs with the necroticarea. E.g. Xanthomonas species (Fig. 7A).

2.Scab/Bacterial canker: Scabs and cankers arecorky outgrowth which is formed on leaves, twigs

and all other plant parts above the ground. Scab isformed by epidermal infection while canker is deepseated. E.g. Clavibacter michiganensis,Streptococus etc (Fig. 7B).3. Bacterial soft rot: Wet, slimy, soft rot thataffects any part of vegetable crops includingheads, curds, edible roots, stems and leaves. E.g.Pseudomonas spp., Erwinia spp (Fig. 7C).4. Bacterial leaf spot/Bacterial spot: Largebrown to black circular areas that start as smalltranslucent spots; water soaked, usually on outerleaves. E.g. Xanthomonas campestris strains (Fig.7D).5. Bacterial wilt: Plant wilt rapidly and die withoutany spotting or yellowing; vascular tissue appearsbrown and water-soaked; white ooze appearswhen pressure is applied to affected tubers orstems. E.g. Ralstonia solanacearum (Fig. 7E).6. Bacterial blight: Water-soaked spots on leavesand stipules which become dark-brown andpapery in warm weather or black in cool weather.E.g. Pseudomonas syringae strains (Fig. 7F).7. Bacterial speck: Small dark spots surroundedby a yellow halo on leaves; dark raised specks onfruit. E.g. Pseudomonas syringae strains (Fig. 7G).8. Bacterial brown spot: Water-soaked spotswhich enlarge and become sunken and tan withdistinctive reddish-brown margins. E.g.Pseudomonas syringae strains (Fig. 7H).9. Tumors and Galls: In many bacterial diseasesthe effect of invasion by the pathogen ishyperplasia and hypertrophy of invaded tissues.As a result, tumours develop on the affectedorgans. E.g. Crown gall tumors by Agrobacteriumtumefaciens (Fig. 7I).

Symptoms caused by viruses:The most obvious symptoms of virus infectedplants are usually those appearing on the leavesbut some viruses may cause striking symptoms onthe stem, fruits and roots.a. Local: These are the symptoms produced atthe site of artificial inoculation on leaves with virus.-Chlorotic local lessions: Infect cell loosechlorophylls and other pigments. Ex. TMV onCowpea host.-Necrotic local lessions: Infect cell die. Ex. TMV onNicotiana glutinosa host.-Ring spot local lesions: Consist of central groupof died cells near inoculated area (Necrotic ring)Ex. Potato Virus: On Chenopodium amaranticolarhost.b. Systemic: In almost all viruses of plantoccurring in field, the virus is present throughoutthe plant. Such types of disease includedecolouration in patches on leaves, sharpness of


boundaries and distribution and discolouration oflamina.1. Mosaic: Light green yellow or white areasintermingled with normal green of leaves of fruit orof whitish areas are intermingled with the areas ofthe normal colour of flowers or fruits. Example:Streak or stripe (Red stripe of jowar), Vein clearing(BCMV), Vein banding (Beat curly top) and Interveinal mosaic light discolouration restricted inbetween veins (Fig. 8A-D).

Fig. 8. Symptoms of viral diseases. A. Chlorosis,B. Ring spot, C. Vein clearing, D. Vein banding, E.

Mottling, F. Leaf curl.

2. Mottling: If the discoloured patch of avariegated leaves are rounded the variegation isusually designated as mottling (Fig. 8E).3. Malformation: This includes uneven growth ofleaf lamina leaves becomes curled, brittle (Crinkling) and show, prominences anddepressions (puckering) upward and downwardcurling, vein distortion, leaf enation, galls andtumours (Fig. 8F).4. Stunting and premature defoliation: Diseaseis characterized by under development of tissueas a result of which normal growth of plantbecome arrested and suppressed leads to thestunted growth of the plant and prematuredefoliation.5. Others: Other viral symptoms includeblistering, (Dark green area may be raised to giveblistering effect), enations (These are the outgrowth in different shape and form either onveins), leaf roll, dwarfing galls and stem pitting etc.Symptoms caused by mycoplasmas,spiroplasmas and fastidious bacteria:(i) They are known to cause “Yellows” disease inplant. Economically important plant diseasecaused by mycoplasmas are sandle spike asteryellows, mulberry dwarf, grassy shoot ofsugarcane, citrus greening, sesame phyllody, littleleaf of brinjal, etc. (Fig. 9). The plants give a bushyappearance, show stunting growth and fail to

produce flowers and fruits. The flowers commonlybecome phyllody.(ii) Spiroplasmas are helical prokaryotes lacking arigid cell wall. Unlike Phytoplasma, they can becultured on artificial media. They transmittedmostly by leaf hoppers. Common symptoms dueto spiroplasmas include citrus stubborn(Spiroplasma citri), leaf roll, yellow dwarf of rice,pear decline, corn stunt, etc.(iii) On the other hand fastidious bacteria alsocalled RLO (Rickettesia Like Organisms) confinedeither to phloem or xylem of the host plant andcauses disease. Stunting is the main diseasecaused by RLO e.g. Sugarcane ratoon stunting(Clavibacter xyli pv. xyli) and Bermuda grassstunting.

Fig. 9. Symptoms of phytoplasmal/spiroplasmaldiseases. A. Little leaf, B. Citrus stubborn, C.

Phyllody.

Symptoms caused by viroids:Commonsymptoms include retardation of plant growth andstunting. Potato plants infected with the potatospindle tuber viroid are smaller than healthyplants. The diseases tubers are spindle shaped.Stunting is the important symptom of tomatoplants affected by the tomato bunchy top viroid,hop plants infected by the hop stunt viroid andchrysanthemum plants infected by thechrysanthemum stunt viroid and thechrysanthemum chlorortic mottle viroid. Viroids arehighly contagious and mechanically transmitted.Potato spindle tuber viroid has been reported to betransmitted by aphids, grass hoppers, flea beetles.Phanerogamic plant parasites: There are fewseeds plants called flowering parasites(Phanerogams) which are parasitic on livingplants. There are two types of phanerogamicparasites.a. Root parasites: They include Striga (Partialroot parasite which attacks sugarcane jowar,Maize, cereals and millets; Fig. 10A) andOrobanche (Complete root parasite which attacktobacco, tomato, brinjal, cabbage, cauliflower Fig.10B).b.Stem parasites: They include Dodder (CuscutaFig. 10C) (Complete stem parasite which attacks


attacks berseem alfalfa, clover, flax, onion, potato,ornamental and hedge plants) and Loranthus(Partial Stem Parasite which attacks mango,citrus, apple, guava; Fig. 10D).

G. Disease diagnostic proceduresProper diagnosis may be extremely important inpreventing the problem on other plants or inpreventing the problem in the future. How does aplant pathologist go about diagnosing plantproblems? The diagnostician must have very goodobservation skills, and s/he also needs to be agood detective. It is important to keep an openmind until all of the facts related to the problemcan be collected. The possibility of multiple causalfactors must also be considered. Controlmeasures depend on proper identification ofdiseases and of the causal agents. Therefore,diagnosis is one of the most important aspects ofa plant pathologist's training. Without properidentification of the disease and the disease-causing agent, disease control measures can be awaste of time and money and can lead to furtherplant losses. Proper disease diagnosis is thereforevital.

Fig. 10. Phanerogamic plant parasites: A. Striga;B. Orobanche; C. Cuscuta; D. Loranthus.

Sample collection methods: Before going to thefield for the collection of diseased plant samplesthe field kits to be taken with are plastic and paperbags, pruning shears, pruning saw, wire twist ties,paper towels Knife, hatchet, increment borer,plastic/rubber gloves, trowel, shovel, soil probe,rubber bands, hand lens 5-10X, forms, pencil,labels vials/jars with lids, padded collection boxes,

camera, maps, field manuals, disinfectant forhands & tools, portable soil pH and soluble saltsmeter. After deciding what to include in thesample, the following procedures for obtaining,packaging, and submitting the sample aresuggested:a. Obtain fresh material in reasonable quantity,several examples of the various symptoms beingexpressed. Be certain to include as manyidentifiable stages of the disease as arerepresented. Most recently developed symptomsusually afford the best material for diagnosis.b. Lift roots carefully so as not to leave feederroots or rotted roots behind. Include about a liter ofsoil for pH, soluble salts, and possibly a nematodeassay.c. Place samples in appropriately sized plasticbags, including a paper towel for a blotter, ifsample is very wet. Duplicate dry samples arerecommended if the sample is succulent or fragile.d. Wrap a wire twist-tie around stem at ground lineto keep soil off of above-ground plant parts.Accurately label samples. Place the entire samplein a paper bag or an unsealed plastic bag.e. Keep samples cool, protected from crushing.f. Gather following information from the grower:1. Host: Cultivar/variety; age; propagationmethod; site prep; names; dates and rates offertilizer, pesticide history and schedule*, growthregulator applications; pruning; pinching;transplant; omissions or additions to usual /conventional culture program.2. Irrigation: Frequency, rate, timing; waterquality; determination of need.3. Soil/media: pH, soluble salts, texture, drainage,homogeneity, aeration, temperature, plantingdepth, cultivation, cropping history, earthmoving/construction, burial/disposal site, trashburning.4. Environmental conditions: Temperature,humidity, ventilation, wind, lightning, exposure,light intensity, air quality, method of heating andcooling, etc. during syndrome development.5. Date of first symptoms and rate of syndromedevelopment, coincident with any treatment orenvironmental event.6. Recent human, animal, insect, mite activityaround or on symptomatic plants.7. Habits of plants in question, predisposition(plant made more susceptible) by cultural orenvironmental conditionsg. Make pertinent observations.1. Spatial and chronological pattern of disease incrop, on individual plants. Are symptoms differentor consistent, uniform or scattered?


2. Are symptoms spreading across crop orprogressing on individual plants?3. What is the frequency and intensity of thesyndrome?4. Any signs of pathogen/causal agent? (Fruitingstructures, chemical residues, insects/mites, frass,etc.).5. Any evidence of host recovery?6. Nearby plants (same or different) show anysymptoms? Are root zones shared?7. Inspect interior, crown, roots of plant. Cut openstems, crowns, flowers, fruits, and roots. Are thereany hidden, internal symptoms/signs of disease?Sample Submission methods: The methodsinclude:a. Take samples before applying pesticides,otherwise the ability to recover pathogens may belimited.b. Submit generous amounts of plant materialrepresenting a range of symptoms.c. Don’t add water or pack a sample that is wet.d. Keep samples refrigerated after collection untilthey are submitted. After collecting good samples,do not allow them to bake in the sun or on theback seat of a car prior to submission becausedoing so will ruin them.e. Do not mix different samples in the samesubmission bag. Moisture from root samples willcontribute to the decay of foliage samples if theyare mixed together.f. Plant disease identification procedures do notutilize soil. Excess soil can be hand shaken fromroot systems, but leave enough soil to keep rootsat field moisture levels.g. Please mark sample packages with “Warning” ifsample has thorns or spines.h. All samples must be accompanied with acompleted Plant Clinic Diagnostic Form. Theseare available at all county Extension offices oronline. Give complete information on the form andkeep it separate from the sample. Complete aseparate form for each sample and plant problem.i. Remember to note recent pesticide history onthe Plant Diagnostic Form accompanying thesample.j. Mail samples early in the week to avoid theweekend layover in the carrier facility.h. For emergency samples, use overnight courierservices or surface mail. Complete mailingaddresses and map locations are necessary ifowners want to be informed of diagnosis or sitemust be revisited.Diagnostic methods: Diagnostic tests foridentification of biotic causal agents: A majorproblem in identification of biotic causal agents isthe inability of some infectious pathogens to grow

on artificial media. Viruses, as well as some fungi(e.g. powdery and downy mildew causing agents)and some prokaryotes (e.g. phytoplasmas),require a living host in order to grow. In caseswhere the plant pathogen is difficult or impossibleto grow on artificial media, other methods may beused for their detection, such as the use ofserological tests for viruses. Viral identification isoften accomplished utilizing ELISA (enzyme-linkedimmunosorbent assay). Other techniques used forthe identification of viruses include negativestaining and electron microscopy to view the viralparticles in plant tissue or suspensions. PCR andELISA tests, as well as other laboratory tests, maybe used for organisms that will grow on artificialmedia. Additional tests may include analysis offatty acids of organisms, carbohydrate utilization(i.e. BIOLOG test), and enzyme activity testing(i.e. pectinase, isozyme patterns).Diagnostic tests for identification of abiotic plantdisease causal agents:It is extremely important tolook for abiotic factors that may be important inobserved symptoms. Soil and water tests may benecessary to determine pH, nutrient composition,salinity, and other factors such as pesticideresidues that may induce various symptoms. Itmay also be important to get samples of planttissue analyzed for nutrient content to determine ifthere is macro- or micronutrient deficiencies ortoxicities.Plant Disease Management: The goal of plantdisease management is to reduce the economicand aesthetic damage caused by plant diseases.Traditionally, this has been called plant diseasecontrol, but current social and environmentalvalues deem “control” as being absolute and theterm too rigid. Disease management might beviewed as proactive whereas disease control isreactive, although it is often difficult to distinguishbetween the two concepts, especially in theapplication of specific measures.Principles of plant disease management: Thebasic principles are:Avoidance of pathogen: It comprises properselection of geographical areas, selection of thefield, sowing date, choice of disease escapingvarieties, selection of diseases free seeds andplanting stock and cultural practices.Exclusion of the pathogens: It includesquarantine measures, seed certification, plantdisease notification and prevention of sale ofdiseased plants.Reduction and eradication of pathogeninoculum: This can be performed by adoptingcultural, physical, mechanical, biological andchemical practices.


Resistance to pathogens: Host resistance andproduction of resistance varieties.Integrated approach: It comprises ofcombination of disease management strategieswith overall aim to develop sustainable system ofdisease management based on a soundunderstanding or whole crop ecosystem.Disease epidemiology and factors affectingspread of disease: Epidemiology or epiphytologyis the study of the outbreak of disease, its course,intensity, cause and effects and the various factorsgoverning it. Based on the occurrence andgeographical distribution they are classified asendemic, epidemic and sporadic which aredescried earlier. An epidemic may causewidespread and mass destruction of crop in ashort time or may persist for long periodsdepending upon the three factors host, pathogenand environment. A disease is sometimessporadic and assumes epidemic proportions underspecial circumstances. The essential conditionsfor an epiphytotic or the factors governingepidemics can be grouped under the three headsi.e. Nature of host; Nature of the pathogen andEnvironment.Components of integrated diseasemanagement: The components of IDM includequarantine & regulatory measures, cultural,genetic resistance, physical and mechanical,biological and chemical.Quarantine and regulatory measures:-Plant quarantine is the legally forced restriction onthe movement of diseased plant materials or offungi, bacteria or viruses that cause disease inplants.-The legislation has been placed on thestatute-book in most agriculturally advancedcountries. When plant pathogens are introducedinto an area in which they did not previously exist,they are likely to cause much more catastrophicepidemics than do the existing pathogens.-Some of the worst plant disease epidemics thathave occurred throughout the world, for examplethe downy mildew of grapes in Europe and thebacterial canker of citrus, the chestnut operation ofthe quarantine regulations.-It is extremely difficult to predict accuratelywhether an exotic organism will becomeestablished, and once established, becomeeconomically important.

-The purpose and intent of the Quarantine Act in acountry is to prevent the introduction of any insect,fungus or other pest, which is or may bedestructive to crops.

-Further, the significance of Plant Quarantine hasincreased in view of Globalisation andliberalisation in International trade of plants andplant material in the wake of Sanitary andPhytosanitary (SPS) Agreement under WTO.-The phytosanitary certification of agriculturalcommodities being exported is also undertakenthrough the scheme as per International PlantProtection Convention (IPPC), 1951.Cultural Practices: Cultural practices serve animportant role in plant disease prevention andmanagement. The benefits of cultural controlbegin with the establishment of a growingenvironment that favors the crop over thepathogen. Reducing plant stress throughenvironmental modification promotes good planthealth and aids in reducing damage from someplant diseases.1. Deep ploughing of the field results in exposureof propagules to elevated temperatures andphysical killing of the pathogen. This can beregarded as dry soil solarization. Summerploughing was effective at reducing populations ofcyst nematodes and increasing wheat yield.2. Flooding of the field somewhat resembles soildisinfestation. Long-term summer soil flooding,with or without paddy culture is found to bedecreased populations of soil borne pathogens.3. Sanitation practices aimed at excluding,reducing, or eliminating pathogen populations arecritical for management of infectious plantdiseases. It is important to use only pathogen-freetransplants.4. In order to reduce dispersal of soil bornepathogens between fields, stakes and farmequipment should be decontaminated beforemoving from one field to the next. Reduction ofpathogen survival from one season to anothermay be achieved by crop rotation and destroyingvolunteer plants.5. Avoid soil movement from one site to another toreduce the risk of moving pathogens. Forexample, sclerotia of Sclerotinia sclerotiorumand Sclerotium rolfsii are transported primarily incontaminated soil. Minimizing wounds duringharvest and packing reduces postharvest diseaseproblems. Depending on crops and other factors,soil sanitation can be achieved to some degree bysolarization.

6. Crop rotation is a very important practice,especially for soil borne disease control. For manysoil borne diseases, at least a 3-year rotationusing a non-host crop greatly reduces pathogenpopulations. This practice is beneficial for


Phytophthora blight of pepper and Fusarium wilt ofwatermelon, but longer rotation periods (up to 5–7years) may be needed. Land previously croppedto alternate and reservoir hosts should be avoidedwhenever possible. Vegetable fields should belocated as far away as possible from inoculum andinsect vector sources.6. Weed control is important for the managementof viral diseases. Weeds may be alternate /collateral hosts for many important vegetableviruses. Eliminating weeds might reduce primaryinoculum. Non-host cover crops help to reduceweed populations and primary inoculum of soilborne pathogens.7. Excessive handling of plants, such as inthinning, pruning, and tying, may be involved inspreading pathogens, particularly bacteria. It isadvisable to handle plants in the field when plantsare driest. Because some pathogens can onlyenter the host through wounds, situations thatpromote plant injury should be avoided.8. If applicable, plants can be staked and tied forimproved air movement in the foliar canopy. Amore open canopy results in less wetness,discouraging growth of most pathogens.9. Soil aeration and drying can be enhanced byincorporating composted organic amendments inthe soil. The pathogen inoculum can be reducedby removing plant material (infected and healthy)after harvest.10. Polyethylene mulch can be used as a physicalbarrier between soil and aboveground plant parts.This is an important practice for fruit rot control inthe field for vegetables. Highly UV-reflective(metalized) mulches repel some insects thattransmit viruses as vectors.Genetic resistance: It is the inherent ability of aplant to prevent or restrict the establishment andsubsequent activities of potential pathogens. Aparticular host may be resistance against all racesof the pathogens (i.e. horizontal resistance) ormay be effective against a few races of thepathogens (i.e. vertical resistance). Controlmeasures by the development of new varietiesresistance to diseases are being applied in almostall the economically important plants. If a newvariety with high yield is produced by the breedersand if it is not resistant to the local pathogens andpests, it cannot be recommended to the farmers.Breeding of the disease resistance is achieved byusual methods such as introduction, selection,hybridization, mutation, polyploidy, budding andgrafting. For the resistant varieties farmers shouldcontact to nearest research centres / localextension functionaries.

Physical and mechanical measures: Mechanicaland physical controls kill a pathogens directly ormake the environment unsuitable for it. Thecommon methods are:1. Collect and destroy the disease infected plantparts.2. Soil sterilization at 50-60ºC for about 30 minkills the all soil borne pathogens.3. Some seed borne diseases like loose smut ofwheat (52ºC for 11 min), leaf scald (50ºC for 2-3h), red rot (54ºC for 8 h) and ratoon stunting ofsugarcane (50ºC for 3h), black rot of crucifer (50ºC for 20-30 min) etc. can be treated by hot watertreatment by immersing infected seeds in hotwater at recommended temperature and time.4. Hot air treatment is given to remove excess ofmoisture from plant organs and protect them fromfungal and bacterial attack. Several virus infecteddormant plants are treated by hot air treatment ata temperature ranging from 35-54ºC for 8 h.5. Refrigeration (low temperature treatment) ismost common method used to prevent post-harvest diseases of perishables fruits andvegetables.6. Use various traps like yellow (aphids,whitefly)/blue (thrips) for the control of insectvectors that are transmission carrier of variousviral diseases.Biological Control: The use of biocontrol agentsin disease management is increasing, especiallyamong organic growers. These products areconsidered safer for the environment and theapplicator than conventional chemicals. Examplesof commercially available biocontrol agentsinclude the fungi Trichodermaviride/harzianum and Gliocladium virens, anactinomycete Streptomyces griseoviridis, and abacterium Bacillus subtilis. Bacteriophages(phages) have been found to be an effectivebiocontrol agent for managing bacterial spot ontomato. Phages are viruses that exclusively infectbacteria. Paecilomyces lilacinus is acommon saprobic, filamentous fungus has beenisolated from a wide range of habitats frequentlybeen detected in the rhizosphere of many crops.The fungus has shown promising results for useas a bio-control agent to control the growth ofdestructive root-knot nematodes.Cross protection is also a one of the modern bio-control method for the disease management. Inthis method mild strain of virus or microorganismsis inoculated in host plant. These provideprotection of host plants from those viruses andmicroorganisms which may cause much moresevere damage e.g. papaya ring spot disease,citrus tristiza disease, etc. One of the limitations of


using biocontrol agents is their inability to survivein certain field conditions. However, biocontrolagents have the ability to improve diseasemanagement when integrated with othermanagement options described in this document.

Table 2: Commercially available bio-controlproducts to control plant disease.

Bio controlProduct

Source Target pathogens

BacterialGalltrol Agrobacterium

radiobacter stain 84Crown gall (A.tumefaciens)

Dagger G Pseudomonasfluroscens

Pythium, Rhizoctonia

Actinovate Streptomyceslydicus

Soil borne pathogens

Messenger Erwinia amylovorahairpin protein

Wide spectrum

Kodiak Bacillus subtilisstrain GB03

Fusarium,Rhizoctonia,Alternaria etc.

Bio-save 10LP, 110

Pseudomonassyringae

Postharvest Botrytis,Mucor, Penicillium

BlightbanA506

Pseudomonasfluorescens A506

Erwinia amylovora,russeting bacteria,frost injury

FungiKalisena Aspergillus niger

AN-27Rhizoctonia solani

Biotrox C Fusariumoxysporum (non-pathogenic)

Fusarium oxysporum

Root Shield,Plant ShieldT-22 PlanterBox

Trichodermaharzianum strain,KRL-AG2 (T-22)

Pythium, Fusarium,Rhizoctonia

Soil Gard(Gliogard)

Trichoderma virensGL-21

Rhizoctonia solani,Pythium

Trichodex Trichodermaharzianum

Colletotrichum,Plasmopara,Sclerotinia

Trichopel Trichodermaharzianum and T.viride

Armillaria,Botryosphaeria,Fusarium

Trichojet Trichodermaharzianum and T.viride

Phytophthora,Pythium, Rhizoctonia

Aspire Candida oleophila182

Botrytis spp. andPenicillium spp.

A number of botanicals are also tested againstfungal disease like sheath blight. Somecommercially used botanicals against plantdiseases are extract of Neem (Azadirachta indica,A. Juss), Garlic (Allium sativum, Linn., Eucalyptus(Eucalyptus globulus, Labill.), Turmeric (Curcumalonga Linn.) Tobacco (Nicotiana tabacum Linn.)Ginger (Zingiber officinale Rosc.) and essentialoils of Nettle (Urtica spp.), Thyme (Thymusvulgaris Linn.), Eucalyptus (Eucalyptus globulesLabill), Rue (Ruta graveolens Linn.), Lemon grass(Cymbopogon flexuosus (Steud. Wats.) and Teatree (Melaleuca alternifolia).

Foliar sprays with Neem gold @ 20 ml /l orNeemazal @ 3ml/l has been found to be effectivein reducing sheath blight and increasing grainyield. Leaf extracts of Eucalyptus globosus (5%)and Azadirchta indica (5%) have been proved toexhibit greater antifungal activity against A.brassicae and Albugo candida and showedsignificant reduction in the severity of Alternariablight and white rust diseases.Chemical measures: When all the abovemethods are not-effective and pathogens causedestructive loss of the crops then we should go forchemical measures. Fungicides and bactericidesare an important component of many diseasemanagement programs. It is important toremember that chemical use should be integratedwith all other appropriate tactics mentioned in thischapter. Information regarding a fungicide'sphysical mode of action helps producers improvesfungicide application timing. Physical mode ofaction of fungicides can be classified into fourcategories: protective, after infection, pre-symptom, and anti-sporulant (post symptom).Protectant fungicides include the bulk of the foliarspray materials available to producers. In order tobe effective, protectant fungicides, such as coppercompounds and mancozeb, need to be on the leaf(or plant) surface prior to pathogen arrival.Systemic (therapeutic) fungicides, based on theirlevel of systemic nature are active inside of theleaf (can penetrate at different rates through thecuticle). Systemic fungicides may stop an infectionafter it starts and prevent further diseasedevelopment.

Constraints in IDM and future thrust: Theconsultant group of the IDM Task Force hasconducted as in-depth study of the constraints onthe implementation of IDM in developing countries,which are mainly institutional, sociological,economic and political.a. Institutional constraint: IDM requiresinterdisciplinary approach to solve pest problem.Lack of coordination among different institution isa constraint. Research programme based onfarmer’s need - is lacking.b. Informational constraint: Lack of informationon IDM among farmers and extension worker.Lack of training on IDM.c. Sociological constraint: Some farmers feel itis risky to adopt IDM compared to use ofpesticides alone. Our farmers are habituated tousing more pesticides.d. Economic constraint: Lack of funds fortraining farmers and extension workers on the useof IDM.


These are the some other constraints for theimplementation of IDM:1. By offering seeds, fertilizers and fungicide oncredit to the farmers, fungicide dealers pose athreat to IDM.2. Pesticides companies use mass media liketelevision and newspapers for popularizing theirproducts through attractive advertisements.3. Farmers are addicted to subsidy and theyalways look for some financial support for adoptingNPM methods.4. Bio-pesticides, bio control agents and other IDMcomponents are not readily available.5. Large farmers discourage small farmers inadopting IDM methods by emphasizing more ontheir risky and unstable nature.6. Scientific community is constrained inrecommending use of IDM technology becausefarmers may ask for compensation in case offailures.

THE FUTURE THRUST

All of the above considerations illustrate that byusing fungicides reduction techniques inagriculture is a wise shift in ecologicalstewardship. Recent market trends show thepublic is increasingly recognizing the need to gofungicide-free as organic sales are growing forvirtually every commodity, from vegetables to petfood to lawn care products. Adopting IDMpractices that emphasize fungicide reduction, andorganic practices, provide real-world solutions fora healthier environment.

CONCLUSION

The disease occurs in plant is by biotic and abioticmeans and causes a significant loss in agriculturesystem. The success and sustainability of IDMstrategy, especially with resource poor farmersgreatly depends on their involvement in helping togenerate locally specific techniques and solutionssuitable for their particular farming systems andintegrating control components that areecologically sound and readily available to them.

Training and awareness raising of farmers,disease survey teams, agricultural developmentofficers, extension agents and policy makersremains to be an important factor for thesuccessful implementation of IDM strategies. Alldirect stakeholders including farmers, extensionworkers, and local crop protection techniciansshould have a practical understanding of theecology, etiology and epidemiology of the majordiseases of the crop. Intensive training usingparticipatory approaches should be used toempower farmers with the appropriate knowledgeto become better managers of their own fieldstranslating this knowledge into appropriatedecision-making tools and practical-control tactics.

ENDNOTESHansen, M.A. and Wick, R.L. 1993. Plant disease

diagnosis: present and future prospects.Advances in Plant Pathology, 10: 65-126.

Maloy, O.C. 2005. Plant Disease Management. ThePlant Health Instructor. DOI: 10.1094/PHI-I-2005-0202-01

Morton, V. and Staub, T. 2008. A Short History ofFungicides. Online, APSnet Features. doi:10.1094/APSnetFeature-2008-0308.

Putnam, M.L. 1995. Evaluation of selected methods ofplant disease diagnosis. Crop Protection, 14:517-525.

Shutleff, M.C. and Averre, C.W. 1997. The plant diseaseclinic and field diagnosis of abiotic diseases.American Phytopathological Society, St. Paul,MN.

Stover, R.H. 1962. Fusarium wilt of Panama diseases ofbananas and other Musa species.Phytopathological Paper No. 4, CommonwealthMycological Institute, Kew, UK.

Documents

A Perspective on Integrated Disease Management … DR ABHAY PANDEY A...or more than one concepts of plant disease management. Use of such integrated approach in plant disease management