PLANT DISEASE CONTROL SAMPATH KUMAR BANOTH . MSC . DEPARTMENT OF MICROBIOLOGY KAKATIYA UNIVERSITY WARANGAL-506009
INTRODUCTION:• Plant disease control is emient process in crop yeilding without complete or partial eradication of pathogen,or control measures of disease,one cannot get good crop yeild results without proper control ammendments of disease or pathogen.• Although there are several articals and books on management of plant diseases, one of the recent decade articles entitled “advances in plant health management in 20th centuary” by cook in 2000.• The major aspect of plant disease is to “eliminate or eradicate the pathogen from plant / crop, pre or post harvest to control the disease and loss of crop yeild by the pathogen.”
•Various methods are being followed for controllingthe diseases in plants, though the principle andbasic theme of plant disease control is similar in allmethods which include. 1)AVOIDENCE 2)EXCLUSION 3)ERADICATION 4)PROTECTION 5)IMMUNIZATION
• METHODS USED IN PLANT DISEASE MANAGEMENT : 1) CULTURAL METHODS 2) BIOLOGICAL CONTROL METHODS 3) BREEDING METHODS FOR DISESE RESISTANCE 4) CHEMICAL METHODS 5) PLANT DISEASE ASSMENT METHODS 6) POST HARVEST DISEASE CONTROL
CULTURAL METHODS : Stevans (1960) had discovered the cultural methods of disease control according to him, these measures involve agricultural croping, harvesting and storage, tillage, crop rotation, soil management, growing of resistant varieties, planning of land use, and other related practices. 1. AVOIDENCE OF PATHOGEN : Diseases can be prevented by a proper selection of the land or field, choice of time of sowing, selection of varieties, seed and plant stock and by modification of cultural practices. The aim of these measures is to enable the host to avoid contact with the pathogen or to ensure that the susceptible stage of the plant and favorable conditions for the pathogen not coincide. 2.PROPER SELECTION OF GEOGRAPHICAL AREA : Many fungal & bacterial diseases are more severe in wet areas than in dry areas, crop which are susceptible to these diseases, if grown in wet areas are likely to be effected by plant pathogens. Eg; smut disease of bajra caused by TOLYPOSPORIUM PENCILLARIAE.
3. SELECTION OF FIELD The selection of suitable area or field for cultivation is very important from the point of view of better yeild’s, as well as protection of the crop from the ravages in the case of many soil borne pathogens, Hence it is advisible not to grow in the same field, where there is high incidence of disease appearing, due to build-up of innoculm potential. Eg; the drinage conditions of the field are also important , low lying, water logged fields favour such diseases as red rot of sugarcane and downy mildews of bajra. In case of fruit orchards the selection of suitable site is very important4. CHOICE OF TIME OF SOWING : Pathogens are able to infect susceptible plants only under certain environmental conditions. Eg; Rhizoctina root rot of gram is severe if gram is sown immediately after the rains, due to the pathogen devlops rapidly under high temperate and moisture conditions.5. DISEASE ESCAPING VARITIES Certain varieties escape the onslaught of the pathogen and resist the attack due to their inherent charecteristic’s. Eg; maturing varieties of wheat or pea escape damage due to Puccinia Graminis Tritici and Esiphe Polygoni respectively.
5. DISEASE ESCAPING VARITEISCertain varieties escape the onslaught of the pathogen andresist the attack due to their inherent charecteristic’s. Eg;maturing varieties of wheat or pea escape damage due toPuccinia Graminis Tritici and Esiphe Polygoni respectively.6. SELECTION OF SEED AND PLANTING STOCK :since many plants propagate by vegitative parts, theselection of diseases free planting material, forms a veryimportant control measures.The planting of disease-freefields is often an important control measures for certaindiseases such as red rot of sugar cane and black scruf ofpotato etc.
MODIFICATIONS OF CULTURAL PRACTICES• The distance between plants, time and amount of irrigation ,quantity and quality of fertilizers or organic manures, time and method of planting, mixed croping method, depth of sowing, & so on are some cultural practices which influence the incidence and severity of certain diseases. For eg; tillage, mixed croping ,management of soil water offers a means to manage the associated microbiota directely through water potential and indirectely through gas exchange of the soil.
HERE ARE SOME MODIFICATIONS :• 1. exculsion of innocullum.• 2. seed treatment -> heat, gas, or chemical.• 3. inspection and certification.• 4. qurantine regulation -> domestic, internal, total, embargoes,• First regulated in usa in 1912 known as federal qurantine acts. – In india 1914,as destructive insect and pest act. – In 1951 rome a international plant protection conversion was drawn up which at present has 50 signatory nations.• 5. eradication of pathogen -> works on brekage of infection chain.• 6. roughing -> careful removal of infected plant or parts from field @an entry stage (removing of foci)• 7. eradication of alternate or collateral host.• 8. crop-rotation• 9. sanitation.• 10. heat or chemical treatment of diseased plants.• 11. soil trement.
BIOLOGICAL CONTROL METHODS• The term biological control clearly implies control of a disease through some biological agency, and the term biological agency, means a living micro organism or macro organism other than the diseased or damaged plant acting as host and the pathogen or pest causing the disease or damage.• According to Garrett (1965) “ biological control of plant disease may be defined as any condition or practice whereby survival or activity of a pathogen is reduced through the agency of any other living organism ( except man himself), with the result that there is a reduction in the incidence of the disease caused by the pathogen”.• Eg: Trichoderma viride, a common saprophytic fungus, is able to parasitize the mycelia of other fungi.
DIFFERENT MECHANISMS HAVE BEEN PROPOSED TO EXPLAIN DISEASE SUPPRESSION BY PSEUDOMONAS SPP. THEY INCLUDE :1. Production of siderophores ( iron chelating compounds) which remove iron from the soil environment and make it unavailable to pathogens.2. Anti biosis –various anti biotics have been reported to be produced by members of genus Pseudomonas.3. Induction of resistance, and4. Competitive root colonization.• MYCORRHIZAL FUNGI AS BIO CONTROL AGENTS:• Mycorrhizal fungi have received considerable attention in recent years, the role of these agents of fungal root pathogens is well known ( reid, 1900,Chandra 1992). Several mechanisms have been postulated. These are :
1. Creating a mechanical barrier for the pathogen to penetrate, 2. Inducing thickening of cell walls through lignification and production of other polysaccharides, 3. Stimulation of host roots to accumulate metabolites, 4. Stimulating flavanolic wall infusions, 5. Increasing concentrations of dihydroxy phenols in roots, 6. Producing anti bacterial and anti fungal anti biotics, and 7. Stimulating microbial activity in the root zone. SOIL AMENDMENTS: Many root diseases such as potato scab have been controlled by ploughing organic material into the soil, The organic amendments increase the activity of saprophytic organisms in a flush which results in the abundant liberation of Co2 as a result of the respiratory activity of the microbes. The pathogens sensetive to Co2 are inhibited. Due to the rapid multiplication of microbes in the soil, the available nitrogen in the soil is rapidly utilized by the fast growing saprophytes..
• This results in acute nitrogen scarcity which adversely affects the growth of the pathogens.• Maurer and baker (1965) showed that c/n ratios greater than 25/1 significantly suppress symptoms of been root rot.• Biological control in potato diseases of underground parts has been studied by shrivastava and saksena (1968).• HYPERPARASITISM ;• Certain fungi and bacteria are parasitic on plant pathogens.• Several workers have tried to utilize eudarluca australis (pycinidial stage known as darluca filum) for controling rusts.• Many fungi are known to parasitize phyto pathogenicnematodes.in 1934 rozsypal and schmidt reported a protomycopsis chytridiale which attacks heterodera schachitti.• BACTERIOPHAGES :• In 1917 d’Herelle presented evidence of a transmissible lytic principle that acted on the shiga bacillus, showing that bacteria have their infective diseases too. A number of phages have now been discovered for many phytophatogenic bacteria such as agrobacterium tumefaceians etc but no plant disease has been cured yet by treatment with phage after the diseases has developed.
ENTOMOGENOUS FUNGI :• There are several fungi ,which are capable of growing in the bodies of insects thus destroying them . Scientists are looking for ways of protecting crops against insect pests .in late 1940 with the introduction of DDT, it was felt that a method had been found to destroy insects affecting crops.• One important fungus which has been utilized is entomphthora, about 011 spp are known, mostly as insect parasites.• CHEMICAL METHODS :• Plant diseases play an important role in determining the amount and cost of food. plant pathology must alleviate the food problem by devising new control measures and improving the older ones.• The use of chemical sprays , dusts or seed treatment for protecting plants from the ravages of pathogens is not an innovation of 20th century.• The first landmark in the control of fungal diseases of plants was discovery by anton and debary that the causal agents of many plant diseases are fungi.
•The fungicides used on plants may be classified as,1. Protectants2. Eradicants3. Therapeutants• On the basis of their uptake by mobility within plants.• The fungicides are dealt with below under the following catagories;1. Inorganic copper compounds2. Inorganic mercury compounds3. Sulphur sprays4. Organic sulphur compounds5. Quinone and phenolic fungicides6. Hetrocyclic nitrogen compounds7. Benzene compounds8. organomercurials9. Systemic fungicides10. Organophosphate fungicides11. Antibiotics12. Soil fumigants13. oils
BREEDING FOR DISEASE RESISTANCE : • The use of disease resistant varieties for controlling plant diseases has been termed the “painless method” because it does not cost the farmer anything. • The use of resistant cultivars and hybrids has several other advantages it eliminates the hazards to human health and wild life which is caused by large scale use of dangerous fungicides and pesticides it also reduces pollution which results from the use of poisonous chemicals and their residues, resistant crop varieties check epidemics of pathogens and pests and thus help to maintain the biological balance environment. • A very superior variety of hops (humulus lupulus) was cultivated in western europe. In 1917. taichung native 1 etc.
TYPES OF RESISTANCE :• Plant pathologists commonly divide resistance into monogenic, Poloigenic, and Oligogenic according to wether the resistance is governed by one or many genes, or a few genes resistence can be discribed as genetic, machanical or epidemilogical.• Oligogenic resistance is determined by 2 to several genes• Polygenic resistance involves many genes which are more difficult to analyse and which are known to be included in a large no of diseases such as cotton wilt.FEW STEPS INCLUDED :• Extra chromosomal inheritance• Gene interaction• Modifier genes• Reversal of dominance
• Concept of vertical and horizontal resistance• Methods of selection of resistant geno types• Selection from existing crops1. Selection from crops that escape damage in infected fields2. Pure line selection3. Plant introduction4. Hybriedization5. Selection from wild verities6. Induced mutations
POST HARVEST CONTROL METHODS1. Post harvest diseases types• Bacterial Rots• Fungi• Non Pathogenic Diseases CULTURAL METHODS TO CONTROL P.H.D.C.• Harvesting and Handling• Packaging• Transportation• Storage• Temperature and Relative Humidity• Control of Pre Harvest Infection
STRATEGIES FOR POST HARVEST DISEASE CONTROL1. Orchard Management2. Disinfection and Washing3. Post Harvest Chemical Treatment4. Fumigation5. Fruit Wraps, Waxing, Coating and Packaging6. Heat Treatment7. Irradiation8. Low Temperature Storage9. Controlled Temperature storage10. Maintenance of Host Resistance11. Moderation of Disease Symptoms12. Chemical Treatments, Etc.