Plant Disease Management: Eradication, Methods & Strategies PDF

Plant management strategies: Eradication 1 ⮚Primarilyaim at breaking the infection chain by removing the foci of infection and starvation of the pathogen ⮚Pathogen is established in the region but aims at the removal of the pathogen from the area. ◼Physical method...

Plant management strategies: Eradication 1 ⮚Primarilyaim at breaking the infection chain by removing the foci of infection and starvation of the pathogen ⮚Pathogen is established in the region but aims at the removal of the pathogen from the area. ◼Physical method ◼Cultural Method ◼Chemical Method  Cultural methods of plant disease 2 management  Cultural methods involve the principles of avoidance, eradication, and therapy. The cultural approaches are- Proper selection of geographical Manures and fertilizers: area: Mixed cropping: Proper selection of the field: Mixed cropping: Time of sowing: Barrier crop: Disease escaping Tillage operations: varieties/selection of cultivars: Depth of sowing: Proper selection of seed and Seed rate and plant density: planting material Soil amendments: Roguing: Soil reaction: Eradication of alternate and Soil reaction: collateral hosts: Irrigation and drainage: Crop rotation: Soil moisture: Crop sanitation:  Eradication of the pathogen a) Rouging:e.g. Smuts and virus diseases. b) Eradication of alternate and collateral hosts c) Crop rotation: d) Crop sanitation: e) Soil amendments: e.g. Application of Sulphur (900 Kg/ha) to soil brings the soil pH to 5.2 and reduces the incidence of common scab of potato (Streptomyces scabies). f) Irrigation and drainage: g) Chemical methods h) Physical methods i) Biological PHYSICAL METHODS OF PLANT DISEASE MANAGEMENT  Physical Methods 5 A. Methods of seed treatment  Hot water -Cold water -Anaerobic  Steam -Sun dry -Oven dry B. Methods of Soil treatment  Solarization  Hot water  Steam  Electric 6 Seed treatment  Seed treatment is a process of treating seeds by any physical, chemical, biological or other agents to destroy harmful organisms or to protect the seeds against infection. Objectives of seed treatments  To prevent germination failure and infection of seedling  To destroy external and internal seed borne pathogen 7 Soil treatment Soil treatment is a process by which soil treating chemicals are mixed with soil in few inches depth from soil surface for killing/controlling soil borne pathogens Objectives of soil treatments  To destroy soil borne fungi, bacteria, nematode without destroying natural balance.  Seed treatments 8 Hot water treatment  commonly used against loose smut of wheat (Ustialgo tritici),  black rot of crucifers (Xanthomonas campestris),  parasitic nematodes of rice (Ditylenchus sp) loose smut of wheat (presoaking in normal water (20°C) for 5- 6 hrs, dibbed in hot water after a little above 50°C for 10-15 min)  Seed treatments 9  Cold-water treatment: After presoaking in normal water (20°C) for 5- 6 hrs, the seeds are dibbed in cold-water (16-20°C) for 70-120 hr.  Anaerobic water treatment: soak in water and held under anaerobic conditions for a definite period of time. e.g. Loose smut of barley  Seed treatments 10  Dry heat treatment: Controls TMV of tomato and lettuce seed infected with lettuce mosaic virus can be controlled by treating at 95°C for 80-120 days.  Solar heat treatment: pre-soaked in water for 4-5 hrs at room temperature and then drained and dried on ground under sunshine for 4-6 hrs.  Aerated steam treatment/Aerobic steam treatment: treat dry seed in moving vapour by pressure flow. e.g. Cabbage seeds against Alternaria brassicae (at 56°C for 30 min)  Hot water desinfestation of 11 planting material Banana planting material treated in water of 53ºC for 20 minutes  Soil Treatments 12 Soil solarization 13 14 15 Steaming  Chemical disease control o Employs the use of chemicals that are either generally toxic and used as disinfectants or fumigants or chemicals that target specific kinds of pathogens, as in the case of fungicides, bactericides (or antibiotics) and nematicides. o No substances have yet been found that effectively control plant viruses. o As a last resort, judicious use of chemical applications may be used to mitigate plant disease losses  Terminology Fungicides: A chemical capable of killing fungi. Toxic to pathogen but not phytotoxic e.g. Dithane M45, Tilt, Bavistin etc Fungistatis: that does not kill, stop growth Antisporulants: that inhabit sporulation only without affecting the growth of vegetative hyphae Bactericide: chemical produced by micro-organisms, which destroy or injure living organisms, in particular, bacteria. e.g. Streptomycin Bacteriostatic: that prevent multiplication of bacteria without killing them e.g. Tetracyclines Nematicides: that kills or inhibit nematodes. e.g. Carbofuran 3G Characteristics of a good fungicide  High field performance: determined by  The inherent fungitoxicity  Availability of the active constituent so that it can act against fungi  Good coverage of the host surface  Not or low phytotoxicity  Stability in storage  Stability after dilution to spray strength  Not or low toxicity of human beings and cattle  Fungicide composition  Active ingredient (a.i.)  Carrier e.g. Dithane M-45 ( Mancozeb) Manganous Ethylene Bis-dithiocarbamate + Zn ion  Classification of fungicides On the basis of- A. Source: 1. Organic, 2. Inorganic B. chemical structure or composition: 1. Copper fungicide 2. Sulphur fungicide 3.Mercury fungicide 4. Heterocyclic fungicide 5. Oxanthiin fungicide 6. Benzimidazole 7. Quinone 8. Others  Classification of fungicides C. On the basis of use: o Seed protectants o Soil fungicides (preplant) o Foliage and blossom o Fruit protectants o Tree wound dressers D. On the basis of mode of action o Contact: Dithane M-45, Rovral, Amistar, Blitox-50 o Systematic: Tilt, Folicure, Ridomil-MZ, Score, Ptovax 200 WP  Classification of fungicides E. Classification of fungicides based on the formulation o Wettable powder: A WP is a powder formulation that forms a suspension when mixed with water prior to spraying  Dust: Dusts are free flowing powders containing technical material in the range of 2 to 10 per cent and a very fine dry inert carrier made from talc, kaolline, chalk, clay, nut hulls, or volcanic ash. o Solution o Suspension o Slurry: mixing the WP with a small amount of water form of a thin paste o Paste o Emulsifiable concentrate (EC): An emulsifiable concentrate (EC) formulation is a combination of an active ingredient dissolved in a water-immiscible solvent with emulsifiers.  Methods of Application of fungicide A. Methods of seed treatment B. Methods of soil treatment C. Methods of foliar application  Adjuvants Auxillary agents No fungicidal action Adjuvants are agrochemicals added to crop protection products to enhance the efficacy of active ingredients and improve the overall performance of the product. o Wetting agents: Long chain alcohol o Spreaders: soap o Stickers: Oil, Milk o Dispersing agent: Gelatine, glue, gum o Emulsiferes: Tween 20, petrolium o Saferners: Oleic acid, Glyceride oils  Bordeaux mixture (BM) French Prof. Millardet discovered BM in 1887 o Components: o Methods of preparation o Simultaneous o Dilute solution o Stock solution o Instantaneous o Testing of BM o Colour test o Indicator test o Chemical test Some Nematicides Methods of Application of Nematicides Methods of Application of Nematicides Methods of Application of Nematicides  Antibiotics 31  Antibiotic is defined as a chemical substance produced by one micro-organism which is low concentration can inhibit or even kill other micro-organism.  Because of their specificity of action against plant pathogens, relatively low phytotoxicity, absorption through foliage and systemic translocation and activity in low concentration, the use of antibiotic is becoming very popular and very effectively used in managing several plant diseases.  They can be grouped as antibacterial antibiotics and antifungal antibiotics. Most antibiotics are products of several actinomycetes and a few are from fungi.  Antibacterial antibiotics 32 Streptomycin sulphate Streptomycin is an antibacterial, antibiotic produced by Streptomyces griseus. Streptomycin are streptomycin sulphate is sold as Agrimycin,-100, Streptomycin sulphate, Plantomycin, Streptocycline etc. Agrimycin 100 contains 15 per cent streptomycin sulphate + 1.5 percent terramycin (Oxy tetracycline). This group of antibiotics act against a broad range of bacterial pathogens causing blights, wilt, rots etc.  Tetracycline  Antibiotics belonging to this group are produced by many species of Streptomyces. This group includes Terramycin or Oxymicin (Oxytetracycline). All these antibiotics are bacteriostatic, bactericidal and mycoplasmastatic. These are very effective against seed- borne bacteria. These are mostly used as combination products with Streptomycin sulphate in controlling a wide range of bacterial diseases. Oxytetracyclines are effectively used as soil drench or as root dip controlling crown gall diseases in rosaceous plants caused by Agrobacterium tumefaciens.  Antifungal antibiotics 33  Aureofungin  It is an antibiotic produced in sub-merged culture of Streptoverticillium cinnamomeum var. terricola. It is absorbed and translocated to other parts of the plants when applied as spray or given to roots as drench. It is sold as Aurefungin-Sol. Containing 33.3% Aureofungin and normally sprays at 50-100 ppm. The diseases controlled are citrus gummosis caused by several species of Phytophthora, powdery mildew of apple caused by Podosphaera leucotricha and apple scab (Venturia inaequalis), groundnut tikka leaf spot, downy mildew, powdery mildew and anthracnose of grapes, potato early and late blight etc.  Griseofulvin  This antifungal antibiotic was first discovered to be produced by Penicillium griseofulvum and now by several species of Penicillium, viz., P. patulum, P. nigricans, P. urticae, and P. raciborskii. It is commercially available as Griseofulvin, Fulvicin and Grisovin. It is highly toxic to powdery mildew of beans and roses, downy mildew of cucumber. Principles of Plant Disease Management Md. Mahidul Islam Masum, PhD Professor Dept. of Plant Pathology [email protected] 🞂 The ultimate aim of plant pathology is to control the disease 🞂 Real purpose of agriculture is not to control the plant diseases but to grow profitable crops Management strategies Measure(s) taken to prevent the incidence of the disease, reduce the amount of inoculum and finally minimize the loss caused by the disease It conveys a concept of continuous process which is based not only on the principle of eradication of the pathogen but mainly on the principle of minimizing the damage or loss below economic injury level.  Essential considerations in plant disease Management Θ Benefit-cost ratio Θ Procedures for disease control should fit into general schedule of operations of crop production Θ Control measures should be adopted on a co-operative basis over large adjoining areas. This reduces frequency of applications, cost of control and increases chances of success of control measures Θ Knowledge aspects of disease development are essential for effective economical control. Θ Prevention of disease depends on management of primary inoculum Θ Integration of different approaches of disease management is always recommended  Knowledge required for effective and economic control o Etiology: diagnosis of the disease and identification of the causal agent o Disease cycle: mode of penetration and dissemination, primary and secondary infection etc o Disease reactions: different aspects of host- pathogen system o Environment: favorable environment and host predisposing factors Objectives Θ reducing initial inoculum or Θ reducing rate of infection Principles It means different types of approaches/measures taken towards plant disease control. All measures under different methods of plant disease management works through six distinct and well-defined principles namely-i) Avoidance, (ii) Exclusion, (iii) Eradication, (iv) Protection (v) Vertical & Horizontal Resistance and vi) therapy Methods Methods are the steps, techniques or devices of application of the principles. Depending on the nature of the agent employed, the measures taken for the management of plant / crop disease can be classified as regulatory, cultural, biological, physical and chemical method. Plant Disease Control PLANT DISEASE MANAGMENT Plant disease management principles developed on a basis of well understand host protection coverage system, called immunization- prophylaxis system. Principles : Plant Disease Management A.Prophylaxis 1. Exclusion of inoculum: 2. Avoidance: 3. Eradication: 4. Protection: B. Immunization 1. Genetic Resistance 2. Induced Resistance Plant disease management strategy  Prophylaxis ❑ It consists of developing and using a set of practices to preserve health and prevent the spread of the disease ❑ Protection of the host from exposure to pathogens or infection and from environment which is favourable for disease development. 1. Exclusion of inoculum: ⮚Preventing the inoculum from entering or establishing in the field or area where it does not exist. ⮚Legal restriction of movement of commodities ⮚Disease free area remains disease free. 2. Avoidance 3. Eradication: 4. Protection:  Prophylaxis 1. Exclusion of inoculum: 2. Avoidance: Enables the host to o avoid the contact of the pathogen o avoid the susceptible stage of the host and o avoid the environment favourable for growth of pathogen 3. Eradication: ⮚ Primarily aim at breaking the infection chain by removing the foci of infection and starvation of the pathogen ⮚ Pathogen is established in the region but aims at the removal of the pathogen from the area. 4. Protection: Application of chemicals to prevent the infection by creating a chemical toxic barrier between the plant surface and the pathogen  1. Exclusion of the pathogen 1. Quarantine Rules and regulations issued prohibiting the movement of insects and diseases and their hosts from one place 2. Others measures a) Seed treatment Seeds are exposed to the heat, gas and chemical treatments to exclude the pathogen present in or on them b) Restricting movement of vectors  2. Avoidance of the pathogen a. Proper selection of geographical area b. Proper selection of the field c. Adjusting time of sowing d. Disease escaping varieties e. Proper selection of seed and planting material f. Modification of cultural practices Crop rotation, Tillage, Sowing depth, Mixed cropping, Soil moisture, Soil fertility.  3. Eradication of the pathogen a) Rouging: e.g. Smuts and virus diseases. b) Eradication of alternate and collateral hosts c) Crop rotation: d) Crop sanitation: e) Soil amendments: e.g. Application of Sulphur (900 Kg/ha) to soil brings the soil pH to 5.2 and reduces the incidence of common scab of potato (Streptomyces scabies). f) Irrigation and drainage: g) Chemical methods h) Physical methods i) Biological 4. Protection Preventing infection by creating a chemical toxic barrier between the plant surface and the pathogen. Methods 1. Seed treatment 2. Soil treatment 3. Foliar application  Plant Quarantine Plant quarantine (PQ) is defined as “a legal restriction on the movement of agricultural commodities for the purpose of exclusion, preventing or delaying the entry of a new or stronger (virulent) pathogens (pests) and diseases in uninfected areas”. PQ: All activities designed to prevent the introduction or spread of quarantine pests or to ensure their official control Purpose: Exclusion, prevention or delay in establishment of plant diseases in the area where they are not present previously.  Types of Plant Quarantine A. Based on the use of locality, plant quarantine is divided into two types- 1. Domestic plant quarantine: restrict the movement of a disease from one place to another within the same country. 2. International plant quarantine: restrict the movement of a disease from one country to another.  Types of Plant Quarantine B. Based on the nature of use of plant quarantine 1. Exclusive plant quarantine: prohibit importation of plant materials from a specified area into a stated or new area. Exclusive PQ may be two types: Total embargo: prohibit entry of all kinds of plant materials from a specified area. Specific embargo: prohibit entry of specific plant or plant parts from a specified area.  Types of Plant Quarantine 2. Regulatory plant quarantine: allow the entry of plant materials under certain conditions: Inspection and certification- that the shipment is pathogen free Disinfection and certification- that the shipment has been properly treated to make it pathogen free. Isolation and certification- that the seed crop was grown in an isolated area free from dangerous pathogens Phytosanitary certificate: It is an official certificate from the country of origin, which should accompany the consignment without which the material may be refused from entry.  Diseases came from different countries Rice blast in 1918 from the Philippines Potato late blight in 1963 from Holland Banana bunchytop in 1940 from Srilinka Powdery mildew in 1910 from Europe Unless quarantine regulations are scientifically sound and administratively feasible it can not be successful. Nature of the pathogen(s) Mode of dissemination of the pathogens Infection process(s) of the pathogens Host range of the pathogens Natural barrier to its distribution Quarantine pathogen Pathogen present in other country but not inside the country. Pathogen distributed in defined area but absent in other part/area of the country.  Pathogens under PQ rules Quarantine pathogens are classified into three categories: Category A: do not occur in the importing country and it can cause infection in epidemic form frequently. Example- Potato black wart: Synchytrium endobioticum Wheat yellow rust: Puccinia striformis Rice powdery mildew: Erysiphe graminis pv oryzae  Pathogens under PQ rules Catergory B: Pathogens are present in the importing country, are occasionally destructive, cause epidemic time to time. Example- Potato late blight: Phytophthora infestans Rice blast: Pyricularia oryzae Catergory C: includes all common pathogens ordinarily present in the importing country as minor pathogens. Example- Rice brown spot: Bipolaris oryzae  Suggested regulations Category A: Total embargo or specific embargo or regulatory PQ Category B: Regulatory PQ Catergory C: Regulatory PQ why?  Plant quarantine laws Plant quarantine laws were first enacted in France (1660), followed by Denmark (1903)and USA (1912). These rules were aimed at the rapid destruction or eradication of barberry bush which is an alternate host of Puccinia graminis tritici. In India, plant quarantine rules and regulations were issued under Destructive Insects and Pests Act (DIPA) in 1914.  Plant quarantine laws in Bangladesh In Bangladesh, it was issued under Destructive Insects and Pests Rules in 1966 (Plant Quarantine) 1989: Destructive Pest and Pathogens Act. 1992: Plant Quarantine Act Plant Quarantine Act, 2011 has been approved by the Parliament in March, 2011 Quarantine at international level The International Plant Protection Convention (IPPC) promotes action to protect plants. Codex Alimentarius sets sanitary and technical standards for food safety The Office International des Épizooties (OIE) – the world Animal health Organization – deals with animal health  Phytosanitary Applications in Bangladesh Current practices Quarantine Stations at Ports and Borders Issuance of Phytosanitary Certificates for Exports Pest Surveillance by Department of Agricultural Extension (DAE) Institution involved: Plant Quarantine Wing (PQW), DAE NARS Institutes Ministry of Agriculture (MoA).  PQ stations in Bangladesh Quarantine station: Official station for holding plants or plant products or other regulated articles, including beneficial organisms, in quarantine At present 30 plant quarantine stations are functioning in the following entry points of Bangladesh- a) Airports: Hazrat Shah Jalal International Airport, Dhaka. Hazrat Shah Amanat International Airport, Chittagong. Osmani International Airport, Sylhet b) Seaports: Chittagong Seaport, Chittagong. Mongla Seaport, Khulna.  PQ stations in Bangladesh c) Land Border Check Post: 1.Benapole, Jessore 13. 14.Bibirbazar, Comilla 2.Darshana, Chuadanga. 14.Kamalpur, Jamalpur 3.Tamabil, Sylhet. 15.Belunia, Feni 4.Burimari, Lalmonirhat. 16.Betli (Fultali), Moulvi bazaar 5.Teknaf, Cox's Bazar 17.Chaltapur, Moulvibazar 6.Akhaura, Brammanbaria 18.Haluaghat, Mymensingh 7.Hilli, Dinazpur 29.Birol, Dinajpur 8.Sonamosjid, Chapinababgonj 20. Bianibazar, Sylhet 9. Rohanpur, Chapinababgonj 21. Vurungamari, Kurigram 10.Bhomra, Satkhira. 22. Nakugao, Sherpur 11.Bangla Bandha, Panchagarh 23. Daulatganj, chuadanga 12. Jakiganj, Sylhet d) River Port: Narayangonj. e) ICD, Kamalapur, Dhaka. DISEASE FORECASTING AND ASSESSMENT OF CROP DISEASES & YIELD LOSSES  Disease Forecasting The prediction of probable outbreaks or increase in intensity of plant disease in a specified area or region ahead of time so that suitable control measures can be undertaken in advance to avoid losses. It is an advance warning/ forewarning to prevent the outbreak of disease and to cover the crop with a protective chemical before infection starts. In practice, it is the use of weather data, frequently combined with biological data (infection period of disease), to predict disease incidence. Objectives of Disease Forecasting To give advance notice of the necessity for control measures To reduce disease intensity To save time, money and energy of the growers for control without risking crop health and also avoids the environmental pollution  Information needed for Disease Forecasting Knowledge of epidemiology is necessary for accurate forecasting. 1. Host factors 2. Pathogen factors 3. Environmental factors PRINCIPLES The nature of the pathogen [ monocyclic or polycyclic ] Effects of the environment on stages of pathogen development. The response of the host to infection [age-related resistance ] Activities of the growers that affect the pathogen or the host. Pre-Requisite of Plant Disease Forecast The crop must be a cash crop. The disease must cause economically significant damage in terms of yield loss or quality. Disease incidence must fluctuate from season to season Control measures must be available at an economically acceptable cost. Reliable means of communication with farmers. Growers must have sufficient man power and equipment to apply control measures when disease warning is given  Uses of disease forecasting Forecasting or assessment of disease is important for crop production management For timely plant protection measures : Information on whether the disease status is expected to be below or above the threshold level. Loss assessment : Forecasting actual intensity of loss and yield reduction can be predicted. Methods for Disease Forecasting Forecasting based on climatological method Forecasting based on primary inoculum Forecasting based on correlative information Use of computer for disease forecasting BLITECAST-late blight of potato EPIDEM- Early blight epidemic in tomato TOMCAST- anthracnose, Septoria leaf spot and early blight on tomatoes EPIMAY- Southern Maize leaf blight EPIVEN-Apple scab 1. Forecasting based on primary inoculums Presence of primary inoculum, its density and viability are determined in the air, soil or planting material. Occurrence of viable spores or propagules in the air can be assessed by using different air trapping devices. In the case of soil-borne diseases the primary inoculum in the soil can be determined by monoculture method. E.g. Loose smut of wheat, ergot of pearl millet and viral diseases of potato. 2. Forecasting based on weather conditions Weather parameters like temperature, relative humidity, rainfall, light, wind velocity etc., during the crop season and during the inter crop season are measured. Weather conditions above the crop and at the soil surface are also recorded. Forecasting based on weather conditions given by late blight of potato(Dutch rules). Dutch rules (in Holland) (Van Everdingen, 1926) Night temperature below dew points for at least 4 hours Minimum temperature of 10°C or slightly above Mean cloudiness on the next day of at least 0.8 or more Rainfall during next 24 hours for at least 0.1mm 3. Forecasting based on correlative information Weather data of several years are collected and correlated with the intensity of the diseases. The data are compared, and then the disease is forecasted. Forecasting criteria developed from comparisons of disease observation with meteorological data have been provided for diseases like leaf blotch of wheat, fire blight of apple and barley powdery mildew.  Rice blast forecasting In India, forecasting rice blast (Pyricularia oryzae) is done by correlative information method. The disease is predicted on the basis of minimum night temperature 20-26°C in association with high relative humidity of 90% or above. Computer based forecasting system has also been developed for rice blast in India.  4. Use of computer for disease forecasting In some advanced countries, disease forecasting is done using computers, which gives quick results. One such computer-based program in the USA is ‘Blitecast‘ for potato late blight. Many computer simulation models have been developed to predict plant diseases. Waggoner and Horsfall (1969) Developed the first computer simulation model (EPIDEM) against Alternaria solani causing early blight disease of tomato and potato. Software for calculations Late blight of potato JHULSACAST developed in Western Uttar Pradesh for rainy and non-rainy year India (non rainy years; 7 days moving graph) - RH> 85% for >50 hrs and Temp. 7.2-26.6°C for >115hrs, If above conditions prevail for 7 consecutive days, blight would appear 7-10 days  Late blight of potato Rainy years; 7 days moving graph Measurable rain 01-05 mm for two consecutive days 5-days moving RH> 85% for >50 hrs 5-days moving congenial temperature (7.2-26.6°C) for 100 hrs If above conditions prevail for 7 consecutive days blight would appear 7-10 days  Geographic information system (GIS) ❖Geographic information systems (GIS) and related technologies like remote sensing are increasingly used to analyze the geography of disease, specifically the relationships between pathological factors (causative agents, vectors and hosts, people) and their geographical environments. ❖A GIS is a computer system designed to capture, store, manipulate, analyze, manage and present all types of spatial or geographical data. ❖GIS provide important tools that can be applied in predicting, monitoring and controlling diseases. ❖Use of GIS tools on data collected to identify critical intervention areas to combat the spread of Banana Xanthomonas wilt (BXW).  Methods for developing disease forecasting models Mainly two Empirical method -model develop through climatological method e.g Dutch Rules (1926) Fundamental method -developed by obtaining data from artificial conditions. eg. BLIGHTCAST (1975)  ASSESSMENT OF CROP DISEASES Three assessments are commonly employed 1. Disease incidence 2. Disease severity 3. Loss- the proportion of the yield that the grower will not be able to harvest. Qualitative degradation of produces and quantitative reduction in harvest.  Crop Diseases assessment methods….. What do we actually measure? (The Parameters) Disease offers three parameters for measurement. 1. Disease incidence The proportion of infected host units, out of the total units sampled 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑖𝑛𝑓𝑒𝑐𝑡𝑒𝑑 𝑝𝑙𝑎𝑛𝑡 𝑢𝑛𝑖𝑡 Disease incidence (I)= x100 𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑙𝑎𝑛𝑡 𝑢𝑛𝑖𝑡 𝑎𝑠𝑠𝑒𝑠𝑠𝑒𝑑 2. Severity – the percentage area of diseased tissue/the proportion of the area of a plant or plant organ (e.g. leaf area, seed, root etc) that is affected 𝐴𝑟𝑒𝑎 𝑜𝑓 𝑑𝑖𝑠𝑒𝑎𝑠𝑒𝑑 𝑡𝑖𝑠𝑠𝑢𝑒 Disease severity(S)= x100 𝑇𝑜𝑡𝑎𝑙 𝑡𝑖𝑠𝑠𝑢𝑒 𝑎𝑟𝑒𝑎 3. Loss – diminution of the crop due to a disease. In actuality the harvested yield is measured and the loss will be computed. Loss refers to reduction in either quantity or quality (or both) of yield. Economic Threshold (ET) -ET is that point where growers should take action to prevent the EIL from being reached; it is NOT the point where economic losses will begin to occur. - that level of disease, at which control costs just equal incremental crop returns Economic Injury Level (EIL) - EIL is the point where damage can no longer be tolerated - Lowest population density that will cause economic damage or economic losses will begin.  METHODS OF DISEASE ASSESSMENT… Disease can be measured using Direct methods (i.e. assessing disease in or on the plant material, which could be qualitative or quantitative) or Indirect methods (e.g. monitoring spore population). Obviously direct methods are likely to be more strongly correlated with yield losses in the crop and are therefore to be preferred. However, recent methods involving remote sensing and detection of crop stress due to disease are likely to increase the accuracy of indirect disease measurements. Direct methods are concerned with both the quantitative and qualitative estimations of disease. Direct quantitative methods are largely concerned with measurements of incidence or severity Nematode density and crop loss Early modelling by linear regression of Meloidogyne incognita in tomato and carrot Partial resistance 10000 Partially resistant Susceptible 100 Pf 1 0 0,01 1 100 Pi Measurement of Disease severity  Assessment of Crop Losses There are two separate phases of approach for estimating yield loss due to disease incidence on a crop 1. Field survey Sampling Data Collection Calculation 2. Field experimentation Critical point model Multiple point model and others  Exercise-1: Examples of measuring disease from data collected through field surveys. Disease: leaf blast of rice Number of samples: 50 tillers. Crop growth stage: Post-planting tillering Leaf per sample: 4 / tiller. stage. Total number of leaves (working sample): 200 Land size: 1 hectare Obs. No. Lesion Grade Ratings covered (Number of leaves in this grade) (% leaf area) 1 0 0 75 2 1 1 25 3 10 2 45 4 25 3 30 5 50 4 20 6 >50 5 05 (Sum of disease ratings) % Disease Severity = X 100 Total ratings (Number of plants examined) X Maximum class grade  Exercise –2. Sampling and data collection were as follows : Data obtained : % leaf area diseased. Number of observations : 5. Leaf sample per observations: 5. Total number of leaf (working sample) : 25. Recorded actual yield : 2400 k.g. / hector. Job : Estimate the yield loss. Critical point or single point models are based on a disease assessment that is made at a given time in the plant's life (the critical point) and then related to yield loss. Critical point model represented by a straight line of the equation of regression time  Role of enzymes and other factors in Plant Pathogenesis How Pathogens affect Plants There are many ways in which plant disease pathogens can affect plants ❖By utilizing host cell contents ❖By killing host or by interfering with its metabolic processes through their enzymes, toxins etc. ❖By weakening the host due to continuous loss of the nutrients. ❖By interfering with the translocation of the food, minerals land water.  Chemical weapons of pathogen Enzymes Toxins Growth regulators polysaccharides All plant pathogens except viruses and viriods can probably produce enzymes, growth regulators and polysaccharides They don’t produce substances themselves but induce the host to produce certain substances  Why Secret the Chemicals ? Enzymes –Disintegrate Cell Structures –Interfere With Cell Functions Toxins –Interfere With Membrane Permeability, Functions Growth Regulators, e.g. Auxins, Gibberellins, cytokinins –Increase or Decrease Ability to Divide & Enlarge Polysaccharides –Vascular Pathogens Block Translocation of Water –May Be Used as Toxin  Constituting substances of cell wall Aerial plant surface -primarily of cuticle and cellulose In root (underground parts), - surfaces consists only of cellulose. Cuticle -wax with cutin Epidermal cell wall -may consist of Protein and lignin Therefore, all the substances are substrates of pathogen’s enzymes for degradation.  Constituting substances of cell wall Wall of parenchymatous cells -Cellulose, Pectins, hemicelluloses, and structural proteins Middle lamella -pectins. The chief substances contained in plant cells are proteins , starch, and lipid. Therefore, all the substances are substrates of pathogen’s enzymes for degradation. ❑Enzymes are large protein molecules Enzyme which act as catalysts to bring a specific set of reactants to a specific product. ❑Plant pathogenic enzymes disintegrate the host cells; break food substances present in the cell and interfere with its functioning systems. ❑Enzymes secreted by microorganisms play a key role in disease development. They break down plant substances into smaller molecules, which the pathogen easily absorbs and utilizes for its growth and energy. ❑ Schematic diagram of morphology and arrangement of some cell wall components along with the respective enzymes responsible for the degradation of the cell wall components Hemicellulase Cellulase Proteases Pectinase Proteases Cellulase Hemicellulase Cellulase  Enzymes in Plant Disease Development Cutinases Cutinases, which are the components of the culture, is known to be produced by many fungi and bacteria. Eg-Puccinia hordei Pectinases Degrade pectic substances, which are the chief component of the middle lamella of plant cells. Eg-Phytophthora, Pythium Cellulases Produced by several plant pathogenic fungi, bacteria and nematodes, which plays a major role in softening Eg-Fusarium Hemicellulases Which break down hemicelluloses, are complex mixture of polysaccharides and a major component of primary cellwall. Eg-Sclerotinia sclerotiorum  Enzymes in Plant Disease Development Ligninases Break down most resistant component to enzymatic gradation, lignin Eg-Brown rot fungi, white rot fungi, Xylaria polymorpha Proteases Which degrade proteins Thedegradationofhostproteinsbyproteolyticenzymessecretedbypathogensaff ectstheorganizationandfunctionofthehostcell. Eg-Helminthosporium oryzae Amylases Which breakdown starch into glucose and utilised by the pathogen Fatty Acid is directly utilized by the pathogen. Eg–Manyfungi, bacteria,and nematodes Lipases Which breakdown lipids(phospholipids, glycolipids). Several fungi, bacteria &nematodes. Eg-Sclerotium rolfsii, Botrytis cinerea Plant constitutes Enzymes that degrade substrates Cutins Cutinase. Eg-Puccinia hordei Cuticular wax Mechanical force Pectin substances Pectinases/ pectolytic enzymes/ (polysaccharides) polygalacturonases Celluloses Cellulases produced by Fungi, bacteria (polysaccharides) & Nematodes Hemicelluloses Hemicellulases produced by fungi Lignins Ligninases-mostly by basidiomycetes Proteins Proteases/ Proteinases/ Peptidases Starch Amylases Lipids Lipases/Phospholipases  Examples ▪ Pathogens that produce higher levels of cutinase seem to be more virulent than others. e. g. The germinating spores of a virulent isolate of the fungus Fusarium produced much more cutinase than those of an avirulent isolate of the same fungus. The fungus Botrytis cinerea, which causes numerous types of diseases on many plants, produces a cutinase and a lipase, both of which break down cutin. ▪ In some Colletotrichum-caused anthracnoses, the fungus produces one pectin lyase, a key virulence factor in disease development. ▪ In some diseases, e.g., the bacterial wilt of solanaceous crops caused by Ralstonia solanacearum, pectinolytic enzymes Diagrammatic representation of cuticle penetration by a germinating fungus spore. Constitutive cutinase releases a few cutin monomers from the plant cuticle. These trigger expression of the cutinase genes of the fungus, leading to the production of more cutinase(s), which macerates the cuticle and allows penetration by the fungus.  Growth hormones e.g. Auxins The bacteria inciting hyperplasia or gall formation on plants include- A. tumefaciens, P. syringae pv. savastanoi, Outgrowth is induced through continuous stimulation by auxin such as indoleacetic acid (IAA) by the causal bacteria in intercellular spaces  Extracellular polysaccharide Extracellular polysaccharides or exopolysaccharides (EPSs) are high molecular weight sugar-based polymers synthesized and secreted by many microorganisms. Aggregative polysaccharides act as molecular glue, allowing the bacterial cells to adhere to each other and surfaces. The mechanical blocking of the xylem with a mixture of bacterial cells and EPS dysfunctions water-conducting system.  Disease resistance in Plants Resistance: Ability of a host to restrict or even prevent the attack of pathogens Susceptibility: The inability of a plant to resist the effect of a pathogen or other damaging factor  Types of disease resistance True resistance: It is the ability of plant to withstand, oppose, lessen, or overcome the attack of pathogens due to presence of resistance gene. Disease resistance that is controlled genetically by the presence of one, a few, or many genes for resistance in the plant is known as true resistance. There are two kinds of true resistance: partial, also called quantitative, polygenic, or horizontal resistance and R gene resistance, also called race specific, monogenic, or vertical resistance. Apparent resistance: Disease escape & Tolerance Vertical vs Horizontal Resistance Resistance 1 2 3 4 5 6 Susceptibility Races Vertical Resistance to Races 2, 5, and 6 Vertical vs Horizontal Resistance Resistance 1 2 3 4 5 6 Susceptibility Races Horizontal Resistance to all Races Plants have several layers of defences against pathogens Pre-existing defences Structural Chemical Induced defences – innate immunity Basal defence Resistance genes Systemic Acquired Resistance SAR The gene for gene concept: “For each gene that confers resistance in host there is a corresponding gene in the pathogen that confers virulence to the pathogen and vice versa.”- H. H. Flor, 1942 Table: Quadratic check of gene combinations and disease reaction types in a host-pathogen system (monogenic) Pathogen genotype Host genotype R (Resistant) r (Susceptible) dominant recessive A (Avirulent) AR (-) Ar (+) dominant a (Virulent) aR (+) ar (+) recessive - = Incompatible reaction + = Compatible reaction In general, plants defend themselves against pathogens by a combination of weapons from two arsenals: 1) Structural characteristics that act as physical barriers and inhibit the pathogen from gaining entrance and spreading through the plant and 2) Biochemical reactions that take place in the cells and tissues of the plant and produce substances that are either toxic to the pathogen or create conditions that inhibit growth of the pathogen in the plant.  A. STRUCTURAL DEFENSE MECHANISM I. Pre-existing, which exist in the plant even before the pathogen comes in contact with the plant II. Post-infectional or Induced, i.e, even after the pathogen has penetrated the preformed defense structures, one or more type of structures are formed to protect the plant from further pathogen invasion.  I. Pre formed or pre existing structural defense Some structural defense are present in the plant even before the pathogen comes in contact with the plant. Passive or Preexisting or Pre- infectional structural defense mechanism or static anti-infection structures A. I. i. Waxes and hairs A. I. ii. Cuticle and epidermal cells. A. I. iii. Sclerenchyma cells A. I. iv. Structure and number of natural openings. II. Active or induced or post- infectional structural defense structures: Pathogen penetration through the host surface induced the structural defense mechanism in the host cells. These may be regarded as i. Induced histological (at tissue level) defense mechanism. cork layer, abscission layers and tyloses ii. cellular defense structures (hyphal sheathing). Cork layer: Infection by pathogens induce plants to form several layers of cork cells beyond the point of infection Furthermore, cork layers stop the flow of nutrients and water from the healthy to the infected area and deprive the pathogen of nourishment.. ABSCISSION LAYERS An abscission layer consists of a gap formed between infected and healthy cells of leaf surrounding the locus of infection. Gradually, infected area shrivels, dies, and sloughs off, carrying with it the pathogen. Schematic formation of an abscission layer around a diseased spot of a Prunus leaf. [After Samuel (1927).] (A–C) Leaf spots and shot holes caused by Xanthomonas arboricola pv. pruni bacteria on (A) ornamental cherry leaves; characteristic broad, light green halos form around the infected area before all affected tissue falls off, (B) on peach, and (C) on plum. The shot hole effect is particularly obvious on the plum leaves. TYLOSES Tyloses are the overgrowths of the protoplast of adjacent living parenchymatous cells, which protrude into xylem vessels through pits and completely blocking the further advance of the pathogen in resistant varieties.  ii. Cellular defense structures Hyphal sheathing: The hyphae penetrating the cell wall and growing into the cell lumen are enveloped by a cellulosic sheath (callose) formed by extension of cell wall, which become infused with phenolic substances and prevents further spread of the pathogen. Ex: Hyphal sheathing is observed in flax infected with Fusarium oxysporum f.sp. lini.  B. BIOCHEMICAL DEFENSE MECHANISM I. Pre-existing chemical defense i. Inhibitors o Released by plant in it’s environment o Present in plant cells before infection ii. Phenolics iii. Tannins iv. Glucanases v. Dienes vi. Chitinase II. Induced chemical defense i. Hypersensitivity response (HR) ii. Production of Antimicrobial substances o Phytoalexins o Plantibodies  II. INDUCED CHEMICAL DEFENSE ❖ Phytoalexins:- (Phyton = plant; alexin = to ward off) ❖ Muller and Borger (1940) first used the term phytoalexins for fungistatic compounds produced by plants in response to injury (mechanical or chemical) or infection. ❖ Phytoalexens are toxic antimicrobial substances. ❖ It produced in appreciable amounts in plants only after stimulation by phytopathogenic micro-organisms or by chemical or mechanical injury. ❖ Phytoalexins are not produced during compatable reaction.  Hypersensitivity Response (HR) The HR is a localized induced cell death in the host plant at the site of infection by a pathogen, thus limiting the growth of pathogen The hypersensitive response (HR) is a mechanism, used by plants, to prevent the spread of infection by microbial pathogens.  Biological control Management of plant disease through the use of another (other than the pathogen) biological agent is called biological control. The agent which is used to biological control is called biological agent. Biological agents always act in its viable stage/state  Disease will not occur when- oPathogen is absent oHost is resistant oEnvironment unfavorable to the pathogen oAntagonists are active  What is antagonist? Any organism acting against pathogen. Organism which is antagonistic to the growth, development and reproduction of the pathogen is called antagonist Properties An antagonistic should always selected from the nature of ecological balance Non pathogenic for plant Fast growth or rapid multiplication capacity Fast spread  What can antagonist do? Antagonist reduce disease through Reduction of inoculum of the pathogen Reduction of infection of the host Reduction of severity of attack How can an antagonist do the job? It may inhibit growth or development of the associate It may stimulate to formation of resting spores by the pathogen It may cause lyses of the pathogen Kinds of antagonists i. Bacteria, ii. Actinomycetes, iii. Fungi, iv. Viruses, v. Nematodes Antagonism The relation between the antagonist and pathogen or mechanism/activities of action how the antagonist kill the pathogen.  Methods of biological control 1. Hyperparastism 2. Parasitism/predation 3. Trap crops 4. Antagonistic plants 5. Mixed cropping 6. Microorganism 7. Organic amendments 8. Bacteriophage 9. Cross protection 10. Induced resistance  Biotechnology in Plant Disease Management Biotechnology: It is defined as genetic modification and manipulation of living organisms through the novel technologies such as tissue culture and genetic engineering resulting in production of improved or new organisms that can be used in variety of ways.  Application of biotechnology in plant disease management: 1. Diagnosis of plant diseases 2. Strain improvement of biocontrol agents 3. Transgenics for plant disease management 4. Determination of biochemical nature and the signals 5. Manipulation of resistance of host  1. Diagnosis of plant diseases a) Diagnostic kits helps in identification of plant diseases, viz., bacterial canker of tomato, soybean root rot, viral diseases of potato, etc., at an early stage of development and helps in devising suitable management practices. b) Polymerase Chain Reaction (PCR): Detection of very small amount of pathogen in a sample by amplifying the pathogen sequences to a detectable level. PCR is especially used in plant quarantine.  2. Strain improvement of biocontrol agents: It has the following advantages a) Expanding the range of target species b) Restricting the range of non-target species c) To improve the survival ability or rhizosphere competence d) Expanding the bio-agents environmental range beyond its congenial habitat e) Development of fungicide tolerant strains 3. Transgenics for plant disease management a) Coat protein mediated resistance for papaya ring spot virus in Hawaii islands b) Cloning of resistance genes, viz., Xa 21, bacterial blight resistance gene isolated from African rice, Oryza longistaminata was introduced into cultivable rice, Oryza sativa 4. Determination of biochemical nature and the signals involved in plants reaction to pathogen invasion and disease development. Ex: Host-pathogen interaction has been studied in rice blast disease incited by Magnaporthe grisea. 5. Manipulation of resistance of host by expression of PR-proteins, antifungal peptides, etc. Ex: Expression of multiple PR-proteins (Chitinases and β-1,3 glucanases) in rice enhanced disease resistance to rice sheath blight pathogen, Rhizoctonia solani.  Plant Tissue Culture: In vitro culture of plant cells, tissues as well as organs. Totipotency is the ability of a plant cell to perform all the functions of development which are characteristic of zygote, i.e., its ability to develop in to an entire plant. Important Tissue Culture Techniques Of Importance To Plant Pathology: 1. Meristem tip culture: Cultivation of axillary or apical meristems, particularly of shoot apical meristem, is known as meristem culture eg. Production of virus free plants 2. Protoplast culture: Interspecific, intraspecific and intrageneric hybridization could be done by this technique for strain improvement of biocontrol agents to enhance the biocontrol potential for the management of pathogenic fungi  Gene cloning/ Recombinant DNA technology / Genetic engineering: Integration of specific fragment of foreign DNA into a cell through a suitable vector in such a way that the inserted DNA replicate independently and transferred to progenies as a result of cell division. Recombinant DNA molecule is a vector into which the desired DNA fragment has been inserted to enable its cloning in an appropriate host. Recombinant DNA molecule is produced by joining together two or more DNA segments usually originated from different organisms. Steps in gene cloning: 1. Identification and isolation of the desired gene or DNA fragment to be cloned (Restriction digestion and electrophoresis) 2. Insertion of the isolated gene in a suitable vector (ligation) 3. Introduction of this vector into a suitable organism or cell called host (transformation) 4. Selection of transformed host cells (selectable markers) 5. Multiplication / integration followed by expression of the introduced gene in the host  Vectors used in gene cloning: A vector is a DNA molecule that has the ability to replicate in an appropriate host cell, and into which the DNA fragment to tbe cloned (called DNA insert) is integrated for cloning. Ex: Tumor inducing (Ti) plasmid of Agrobacterium tumefaciens  Integrated Plant Disease Management (IPDM) IPDM: Rationale combination of all possible management practices to keep pathogen population/disease pressure below economic threshold level. Components of IPDM: 1. Regulatory measures (quarantine) 2. Cultural practices 3. Physical methods 4. Biological methods 5. Genetic engineering 6. Chemical methods Main strategies of IPDM: 1. Use of resistant or tolerant cultivars of plants 2. Modification of cultural practices 3. Encouragement and enhancement of biocontrol agents 4. Need based application of pesticides 5. Use of any other strategies that interrupts host- pathogen interactions  Advantages of IPDM 1. Avoids chemical pollution of soil, water, air and food products 2. Avoids fungicides 3. It is an eco-friendly strategy for management of plant diseases 4. It is an economically feasible approach 5. It is a multipronged strategy for efficient management of plant diseases Therefore, IPDM utilizes all suitable strategies in a compatible manner to reduce and maintain pathogen populations at levels below those causing economic losses.  IPDM strategy in rice: 1. Selection of healthy seed 2. Selection of resistant cultivars 3. Removal and destruction of collateral hosts 4. Balanced fertilization 5. Rouging of diseased plants 6. Seed treatment with carbendazim or tricyclazole at 2g/Kg seed 7. Need based foliar application of [email protected]% or [email protected]% for the management of blast. 8. Need based foliar application of validamycin for the management of sheath blight and sheath rot. 9. Soil application of carbofuran granules or foliar spray of any systemic fungicide is followed to manage insect vectors, thereby  IPDM in sugarcane: 1. Collection and destruction of infected crop debris 2. Hot water treatment of setts (520C for 30 min) 3. 3. Hot air treatment of setts (540C for 2-3 hrs) 4. Balanced irrigation and fertilization 5. Avoid selection of seed material from Ratoon crop 6. Need based spray of systemic insecticides to minimize the spread of viral and Phytoplasmal diseases 7. Selection of disease resistant or tolerant cultivars Fungi: Fungi are the eukaryotic, achlorophyllous, nucleated, branched, unicellular or multicellular microorganisms, cell wall consists of chitin and glucan reproduce by the division of vegetative cells, well defined asexual and sexual spores. Bacteria: Single-celled, prokaryotic microscopic organisms that lack nuclei and other organized cell structures  Virus: Infectious nucleoprotein particle that multiply only within living host cell and has the ability to cause disease Nematode: Nematodes are non segmented, usually microscopic worms, under the Phylum - NEMATODA, that inhabit soil, water, and plant tissues.  SYMPTOMS OF PLANT DISEASES Blight- Sudden and rapid death of plant tissue Spot- Isolate and individual lesion on plant organ of limited extent Die back- Dead and drying of twigs and moving downwards Anthracnose-Depressed or sunken lesion in infected plant parts  Rot- Softening and disintegration of plant tissues by enzymes secreted by pathogens Wilt- Loss of rigidity and drooping of plants or plant parts  SIGN Bearing Diseases Rust- Pustules (Blister like) over the infected area of plant Smut-  Mildews- Sclerotium rot- Mosaic