Plant Pathology: Pathogen Effects and Disease Management

Plant Management Strategies: Eradication

• Eradication primarily focuses on breaking the infection chain.
• This is achieved by removing infection sources and starving pathogens.
• Eradication aims for the removal of the pathogen in a region that it is established in.
• Eradication can use Physical, Cultural, and Chemical methods.

Cultural Methods of Plant Disease Management

• Cultural methods utilize avoidance, eradication, and therapy principles.
• Proper Selection of Geographical Area is key.
• Mixed Cropping is a crucial step.
• Manures and Fertilizers are important
• Proper Selection of the Field is important.
• Time of Sowing is a factor to consider.
• Barrier crops should be considered.
• Disease Escaping Varieties and selections of cultivars can be useful.
• Tillage operations are a part of cultural methods.
• Selection of Seed and Planting Material matters.
• The Depth of Sowing can affect plant health.
• Roguing should be considered.
• Seed Rate and Plant Density need consideration.
• Eradication of Alternate and Collateral Hosts is key to disease prevention.
• Soil amendments are important for disease control.
• Crop Rotation can benefit disease control.
• Soil reaction can effect disease.
• Crop sanitation and soil moisture are important.
• Proper Irrigation and Drainage is a key factor for plant health.

Eradication of the Pathogen

• Rouging is the removal of infected or diseased plants from a field.
• Smuts and virus diseases are reasons to use rouging.
• Eradication of alternate and collateral hosts helps control pathogen spread.
• Crop rotation can break disease cycles.
• Crop sanitation reduces pathogen levels.
• Soil amendments are also useful.
• Sulphur at 900 Kg/ha can lower soil pH to 5.2 and reduce common potato scab.
• Irrigation and drainage are helpful.
• Chemical methods, physical methods, and biological methods are used in pathogen eradication.

Physical Methods

• Physical methods are ways to manage the risk of plant diseases
• Methods of Seed Treatment consist of Hot water, Steam, Cold water, Anaerobic, Sun dry and Oven dry
• Methods of Soil Treatment consist of Solarization, Hot water, Steam, and Electric treatments

Seed Treatment

• Seed treatment is a process of treating seeds by physical, chemical, biological, or other methods.
• Treatments destroy harmful organisms or protect the seeds from infection.
• The objectives of seed treatments;
• Prevent germination failure and seedling infection.
• Destroy external and internal seedborne pathogens.

Hot Water Treatment

• Hot water treatment is commonly used against:
• Loose smut of wheat (Ustialgo tritici).
• Black rot of crucifers (Xanthomonas campestris).
• Parasitic nematodes of rice (Ditylenchus sp).
• For loose smut of wheat, presoaking in normal water (20°C) for 5-6 hrs, then dibbed in hot water (above 50°C) for 10-15 min.

Cold and Anerobic Water Treatments

• Cold-water treatment: Presoak in normal water (20°C) for 5-6 hours.
• Next seeds are dibbed in cold-water (16-20°C) for 70-120 hour.
• Anaerobic water treatment: soak seeds in water and hold under anaerobic conditions for a definite period of time.
• This treatment is used for loose smut of barley.

Dry and Solar Heat Treatments

• Dry heat treatment controls TMV of tomato and lettuce mosaic virus.
• Treat at 95°C for 80-120 days.
• Solar heat treatment: pre-soak seeds in water for 4-5 hrs.
• Then drain and dry on the ground under sunshine for 4-6 hrs.
• Aerated steam treatment/Aerobic steam treatment: treat dry seed in moving vapor by pressure flow.
• Apply to Cabbage seeds against Alternaria brassicae at 56°C for 30 min.
• Banana planting material can be treated in water of 53°C for 20 minutes.

Soil Treatments

• Soil treatment is a process by which to treat soil
• soil treating chemicals are mixed with soil in few inches depth from soil surface
• to kill/ control soil-borne pathogens
• Objectives of soil treatments:
• to destroy soil borne fungi, bacteria, nematode
• without destroying natural balance
• Soil solarization is a method of treating soil with heat from the sun
• Steaming is also an effective method

Chemical Disease Control

• Chemicals are generally toxic and used as disinfectants or fumigants.
• Chemicals target specific pathogen kinds in cases of fungicides, bactericides (or antibiotics) and nematicides.
• Substances have not been found that effectively control plant viruses.
• Judicious chemical applications mitigate plant disease losses as a last resort.

Terminology

• Fungicides: Chemicals which are capable of killing fungi.
• Toxic to pathogens while not phytotoxic.
• Examples: Dithane M45, Tilt, and Bavistin.
• Fungistatis: Chemicals which do not kill fungi, but stop growth.
• Antisporulants: Chemicals which only inhibit sporulation without affecting the growth of vegetative hyphae.
• Bactericide: Chemicals which are produced by micro-organisms which destroy or injure living organisms, in particular, bacteria.
  • Example: Streptomycin
• Bacteriostatic: Chemicals that prevent multiplication of bacteria without killing them.
  • Example: Tetracyclines
• Nematicides: Chemicals that kill or inhibit nematodes.
  • Example: Carbofuran 3G

Characteristics, Composition and Classifications of a Good Fungicide

• High field performance: Determined by the inherent fungitoxicity, availability of the active constituent, and good coverage of the host surface.
• Should not be or have low phytotoxicity and have stability in storage with stability after dilution to spray strength.
• Should not be or have low toxicity to human beings and cattle.
• A fungicide composition is composed of an active ingredient (a.i.) and a carrier.
• Example: Dithane M-45 composed of Manganous Ethylene Bis-dithiocarbamate + Zn ion.
• Classification of fungicides:
• Upon their source:
• Organic
• Inorganic
• Chemical composition (Copper fungicide, Sulphur fungicide, Mercury fungicide, Heterocyclic fungicide, Oxanthiin fungicide, Benzimidazole, Quinone and Others)
• Upon their use (Seed protectants. Soil fungicides (preplant), Foliage and blossom, Fruit protectants, Tree wound dressers)
• Mode of action (Contact: Dithane M-45, Rovral, Amistar, Blitox-50 / Systematic: Tilt, Folicure, Ridomil-MZ, Score, Ptovax 200 WP)

Adjuvants

• Agro-chemicals added to crop protection products to enhance the efficacy of active ingredients and improve overall performance. They have no fungicidal action.
• Wetting agents is a type of auxiliary agent, such as Long chain alcohol
• Spreaders: soap
• Stickers: Oil, Milk
• Dispersing agent: Gelatine, glue, gum
• Emulsiferes: Tween 20, petrolium
• Saferners: Oleic acid, Glyceride oils

Bordeaux Mixture (BM)

• French Professor Millardet discovered BM in 1887.
• Methods for its preparation include simultaneous, dilute solution, stock solution, and instantaneous mixing.
• BM Testing includes color, indicator, and chemical tests.

Fumigants and Non-Fumigants use for Nematodes

• Fumigants: true nematicides and multipurpose fumigants which include are applied
  • D-D mixture and 1,3-D (), Dibro methane (),
  • 1,2-dibromo-3-chloro propane (1,2-DBCP)(*), chloropicrin, and methyl bromide (Telone).
  • MIT and related compounds (dazomet, and metam sodium) (Basamid, and Vapam).
• Non-fumigants: dichlofention, fenamiphos, ethoprophos, fosthiazate, cadusafos, aldicarb, oxamyl, and carbofuran
• Nematicide Trade names: Nemacur, Mocap, Nemathorin, Rugby, Temik, Vydate, and Furadan
• Applied Fumigants as: Liquefied gasses, Volatile liquids, Solids (granulate)
• Volatilizes through soil pores as a gas which interferes with respiration.
• Tarping (+/- impermeable plastic sheet) or surface seal by rolling soil surface prevents loss of a.i.
• Non-fumigants application
  • As granulated formulation (microgranules, 1 mm) or liquids (injected into soil, with irrigation, foliar)
  • Interfere with chemoreception of the nervous system, the host’s finding ability, movement, and hatch
  • Applied with precision in row, full field, and various depths
  • Exposure to nontargets, phytotoxicity, and costs are an issue

Antibiotics

• Antibiotics are chemical substance which are produced by one micro-organism, which in low concentrations can inhibit or even kill other micro-organisms.
• High specificity of Antibiotics action against plant pathogens, has relatively low phytotoxicity, gets absorbed through foliage, and causes systemic translocation and activity in low concentration, making it very popular and effectively used in managing several plant diseases.
• Antibiotics are grouped as either antibacterial or antifungal kinds

Antibacterial Antibiotics

• Streptomycin is an antibacterial antibiotic that’s produced by Streptomyces griseus.
• Streptomycin is sold as Agrimycin-100, Streptomycin sulphate, Plantomycin, or Streptocycline
• Agrimycin 100 contains 15% streptomycin sulphate + 1.5% terramycin (Oxytetracycline)
• Effective against a broad range of bacterial pathogens, can cause blights, wilt, and rots.
• Tetracycline: Includes Terramycin or Oxymicin (Oxytetracycline).
• It Is bacteriostatic, bactericidal, and mycoplasmastatic.
• Effective against seedborne bacteria.
• Used as combination products with Streptomycin sulphate in controlling a wide bacterial diseases range.
• Oxytetracyclines use effectively as soil drench or as root dip controlling crown gall diseases in rosaceous plants, which are caused by Agrobacterium tumefaciens.

Antifungal antibiotics

• Aureofungin
  • Is produced in sub-merged culture
  • Of Streptoverticillium cinnamomeum var. terricola
  • Absorbed and translocated to other parts of the plants (when applied as spray/drench)
  • Sold as Aurefungin-Sol (containing 33.3% Aureofungin)
  • Sprays normally at 50-100 ppm
  • Diseases controlled include:
    • Citrus gummosis (caused by Phytophthora).
    • Apple powdery mildew (caused by Podosphaera leucotricha)
    • Apple scab (Venturia inaequalis)
    • Groundnut tikka leaf spot, downy mildew, powdery mildew.
    • Anthracnose of grapes, potato early and late blight
• Griseofulvin
  • Was discovered to be produced by Penicillium griseofulvum/several species of Penicillium (P. patulum, P. nigricans, P. urticae, and P. raciborskii)
  • Available as Griseofulvin, Fulvicin and Grisovin.
  • Is highly toxic to powdery mildew of beans and roses, and downy mildew of cucumber

Effect of Management Strategies

• Disease control is the ultimate aim of plant pathology.
• The real purpose of agriculture is not to control the plant diseases but to grow profitable crops.
• Management strategies: measures taken to prevent the incidence of disease, reduce inoculum amount and minimize the damage caused.
• Management strategies convey concepts of continuous processes, based not only on the principle of eradication of the pathogen, but also on minimizing damage or loss to below economic injury level.

Key Differences: Control Versus Management

• Control
• Kills undesired organisms
• Takes place within a limited time period
• Reduces numbers (up to zero)
• Is a single measure
• Management
• Concerns the entire system
• Uses different strategies
• Takes place during longer period
• Aims to reduce impact to non-injurious level

Characteristics of a successful strategy:

• Is cheap or cost-effective
• Has ease of application
• Is Effective and efficient,
• Must be Accessible
• Environmentally friendly
• Durable

Knowledge Necessary for Control

• Etiology: diagnosis of disease and identification of the causal agent.
• Disease cycle: mode of penetration and dissemination, primary and secondary infection.
• Disease reactions: different aspects of host pathogen system.
• Environment: favorable and predisposing factors.

Objectives and Principles

• Objectives: reducing the intitial inoculum or reducing infection rate.
• Principles:
  • Is measures/approaches taken towards plant disease control
  • Works through 6 defined principals
  • Avoidance
  • Exclusion
  • Eradication
  • Protection
  • Vertical/Horizontal Resistance
  • Therapy
• Methods: are steps, techniques, or devices of application of principles.
  • Depending on nature of agent employed
  • Disease measures are classified as regulatory, cultural, biological, physical, and chemical methods.

Principles of Plant Disease Management

• Plant disease management has principles for how to understand a host protection’s coverage system which is called an immunization-prophylaxis system.
• There are 2 principles that are included:
  • Prophylaxis
  • Immunization
• Prophylaxis
  • Exclusion of inoculum
  • Avoidance
  • Eradication
  • Protection
• Immunization
  • Genetic resistance
  • Induced resistance
• There are a set of practices that must be used to perserve health and reduce the span of disease:
  • Protection of host ( Exposure on pathogen, Enviroment, and Infection)
  • Preventing Inoculum(Entering or establishing field)
  • Leagal restriction of movement
  • Remain disease free
  • Eradication
  • Removing infection breaking, infection of staruation and pathogen
  • Protection
  • Prevent infection, plant toxic barrier and chemical between plate surface.

Avoidance

• Proper geographical area
• Proper field section
• Adjust time zone
• Disease escaping varieties
• Proper seed selection
• Adjust cultural properties

Plant Quarantine

• Defined as a legal restriction on the movement of agricultural commodities to prevent the entry of new pathogens into uninfected areas.
• Encompasses all activities to prevent the introduction or spread of quarantine pests and ensure their official control.
• Purpose: Exclusion, prevention, and/or delay in the establishment of plant diseases to areas where they were not previously present.
• A plant quarantine is based in two locations
• Domestic Plant Quarantine (Same Country) Restriction on the movement of disease and locations
• International Plant Quarantine ( New Country) Restricts the movement of specific disease location to the new country.
• Exclusive Plant Quarantine
• Prohibiting the import of plant material from an unknown location to a specified area - Total Embargo (Prohibit entires of all kind of plant material from location.
• Specific Embargo ( Only Prohibt certain types of plants that may include pest.

Regulatory Plant Quaratine

• This allows the entry of plants but under a few set condiotions to regulate
• Conditions could be:
• Inspected and if infection free.
• Is free from pathogens.
• Undergo isolation to prevent infection.
• Undergo official certifcate without extra materials

Key Details

• Rice Black came from Philippines In 1918
• Potato Late Blight came from Holland in 1963.
• Banana Brunchytop came from Sri Lanka in 1940
• Downy Mildew came from Europe in 1910
• Regulations need to be sound with administrative feasibilty
• Nature of pathogens.
• Mode of dissemination of pathogens.
• Process of infection.
• How pathogens effect host.
• Barrier to disease.
• Plants were distributed inside and outside areas.
• Pathogens effect country inside and outside.
• Pathogens are grouped in three categories based on level and infection amount:
  • Potato black wart: Synchytrium endobioticum
  • Wheat yellow rust: Puccinia striformis
  • Rice powdery mildew: Erysiphe graminis pv oryzae
• 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.
• Plant quarantine regulations
• First enacted in France 1660, the by Denmark and the U.S.
• These rules were aimed to help destroy or eradicate plants to promote agriculture production.

Plant Disease Forecasting

• Forecasting is the prediction of probable outbreaks or increase in intensity of plant disease in a specified area.
• It is an advance warning to prevent disease outbreak and protect crop w/chemicals before disease occurs.
• Weather data is often combined with biological data to predict incidence.
• Forecasting objectives:
• Help give advance notice of necessity for control measures.
• Reduce disease intensity.
• Save the growers time, money, and energy for control without risking crop health, and avoids environmental pollution.
• Knowledge of epidemiology is necessary for accurate forecasting:
• Host factors.
• Pathogen factors.
• Environment factors.
• Principles:
• Pathogen nature.
• Effects of environment on stages of pathogen development.
• Host response to infection.
• Grower activities that affect the pathogen or the host.
• Crop factors:
• Crop must be a cash crop.
• Disease causes significant economic damage.
• Disease incidence fluctuates from season to season.
• Control measures must be available at an economically acceptable cost. Reliable communication with farmers is needed.

Application of Plant Disease Forecasting

• Timely Information which ensures on whether the disease status is expected to be below or above the threshold level.
• A loss assessment; forecasting actual intensity of loss and yield reduction can be predicted.
• Methods to do so:
• Forecasting the climate.
• Forecasting the incoulum
• Compare information
• Computer forecast
• Presence of primay to the air.
• Loess smut , pearl millet and the viral.
• Steps to take.
• Parameter data
• Condition above crops and soil structure
• Blot of Wheat
• Fire Blight.
• Factors of rice. Data related to minimum night temperature and or humidity if the computer.

Application of Computers in Plant Disease Forecasting

• Developed countries are the first who utilize computors to give fast resull
• "Blitecast" is used for late blight forecast
• Developed Models.
  • 14Waggoner :Horssall(1969) to computer and simulate it. And to help with early blight dissaes.

Models Of Plant Disease Measurement

• Tarpped / non tarpped
• depth of area inside soil
• Start of the warm/mild
• Measure based
  • Temperture
  • Nemacur
  • Mocap
  • Nemaothirin
  • Rucky
  • Temik
  • Wylate
  • Furadan

Assessment

• Completely, there are three steps.
• The severity
• The incidence
• The loses with the portion that can be harvested and harvested. Assessment Methods. - What am i measuring and is it based on paramters - Disease which offeres three ways to
• Propotinty of host - Number infected - number with assessed
• Sevority portion to all effects
• Loss : Reduction in quantity or in quantity of total

###Economic Consideration for Disease

• Economic Threshold (ET)
  • The pint were farmers will take action to prevent damage to crop
  • A level to which controls cost match crop production
  • Economic Injury Level (EIL)
• EIL Level when damage cant be tolearted
• Damage : Economoic and high

###Methods of Disease Assessment

• Can be measured using : direct and indirect methods
• Are used strongly with yield loos
• Is to increase the likely of data
• Quantize direct is used. -Nematodes
  • Linear with models

Role Of Enzymes (Plant Diseases )

• Pathogens effeect plants when they utilizes it (Enzymes, Toxins, And More)
• Weaking of crop with continuess loss an translocation
• Pathogens except virous cant produce Ensymes (All PATHGENIC)
• They indunce sustance with host and certian pathogenss.

Why Secret ?

• Disinerigate with function cells - To increase ablitly to enalrge and divided - Vasculiar ,Toxians and more;

All Cells Include::

::

• Areial
• Surface
• In the root, are always only cellious
• Have wax and cution

Plant Defenses

• Large Protiens: Catalyst
• Planthongenic : disintergrat hosts with cell interfence systers
• Enysumes, play a very key role in play function and ability