PHYTOPATHOLOGY 431

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PHYTOPATHOLOGY - 431

• NUSRET ZENCIRCI, PhD.

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TOPIC 1 - The introduction (Agrios, Chapter 1)

• The introduction (Plant Pathology, by Agrios,
  Chapter 1) will cover
• The concept of disease in plants,
• Classification of plant diseases,
• History of plant pathology,
• Importance of plant diseases,
• Diagnosis of plant diseases,
• Identification of a previously unknown disease
  Kochs postulates

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TOPIC 1 - The introduction

• The growth and yield of plants -
• depend on
• Available nutrients and water for the plant,
• Environmental factors light, temperature.
• and reduced by
• Plant pathogens,
• Unfavaroble weather,
• Weeds, and
• Insect pests.
• Though no evidence why not, maybe- for any pain
  or discomfort, plants also suffer from diseases
  like human,
• The disease in plants develops the same way as it
  does in humans / animals.

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TOPIC 1 - The introduction

• Plant pathology is the study of
• the living entities and the environmental
  conditions that cause diseases in plants,
• the mechanisms by which these factors produce
  diseases in plants,
• the interactions between the disease-causing
  agents and the diseased plants,
• the methods of preventing disease, alleviating
  the damage it causes, or controlling a disease
  either before or after it develops in plant.

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TOPIC 1 - The introduction

• The disease-causing agents
• Fungi,
• Bacteria,
• Mycoplasmas,
• Parasitic higher plants,
• Viruses,
• Viroids,
• Nematodes,
• Protozoa.
• These are biotic stresses.

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TOPIC 1 - The introduction

• Plant pathology also studies Plant disorders
  caused by abiotic stresses.
• Excess / imbalance / lack of certain physical,
  chemical factors, i.e. moisture, temperature, and
  nutrients.
• In short Diseasing agents (factors) are
• BIOTIC, 2. ABIOTIC
• Plant pathology utilizes basic techniques and
  knowledge of
• Botany, mycology, bacteriology, virology,
  nematology, plant anatomy, plant physiology,
  genetics, biochemistry, horticulture, soil,
  science, forestry, chemistry, physics,meteorology
  , etc.
• Plant pathology, on one hand, increases our
  knowledge on the causes and the development of
  plant diseases, on the other hand, develops
  control mechanisms against to plant diseases
  Practical goal.

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TOPIC 1 - The introduction The concept of
disease in plants

• A healthy / normal plant With good physiological
  functions to the best of its genetic potential.
• Normal cell division, differentiation,
  development,
• Water and mineral absorbtion from the soil,
• Photosynthesis and translocation of the
  photosynthetic products for utilization or
  storage,
• Storage of food supplies for overwintering or
  reproduction.
• When one of these fails, then, plants become
  diseased.
• In order of disease development
• At the site of affliction Chemical natured,
  invisible.
• Then, widespread histological macroscopic
  manifestation, followed by clear symptoms of
  disease.

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TOPIC 1 - The introduction The concept of
disease in plants

• When disease appears
• Plants weakened,
• Reduced / fully eliminated physiological
  functions,
• The place of infection determines the function
  weakened or totally lost
• Roots (root rots) intreferes water and nutrition
  absorbtion from the soil.
• Flower infections interfere with reproduction,
• etc (See Fig 1).

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Diseases could happen any part of the plant.
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TOPIC 1 - The introduction The concept of
disease in plants
Diseases could happen any part of the plant.
Tomotoe antracnose
Bacterial wilt Melon
Bacterial spot of pepper
Corn leaf blight
Corn smut
NEMATODES ON a. Sugar beet, b. Pepper
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TOPIC 1 - The introduction The concept of
disease in plants

• Disease in plants, then, is
• Any disturbance brought about by a pathogen or an
  environmental factor which interferes with
  manufacture, translocation, or utilization of
  food, mineral nutrients, and water in such a way
  that the affected plant changes in appearance
  and/or yield less than normal.
• How pathogens cause diseases
• Consuming the content of host cells upon contact,
• Killing or disturbing the metabolism of host
  cells through toxins, enzymes, or
  gorowth-regulating substances they secrete,
• Weakening the host by continually absorbing food
  from the host cells for their own use,
• Blocking the transportation of food, mineral,
  nutirents, and water through conductive tissues.

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TOPIC 1 - The introduction Classification of
plant diseases

• Diseases could be classified by
• Symptoms (root rots, rusts, leaf spots, etc),
• Organs (leaf, fruit, foliage diseases, etc),
• Plant types (field crop, fruit, vegetable
  diseases, etc),
• Pathogen types
• indicates the cause, probable development,
  spread, and probable control of the disease.

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TOPIC 1 - The introduction Classification of
plant diseases

• A. Infectious Plant Diseases
• Diseases caused by
• Fungi,
• Bacteria
• Mycoplasmas
• Parasitic higher plants
• Viruses and viroids
• Nematodes
• Protozoa

• B. Nonifectious or physiological disorders
• Too low or high temperature
• Lack or excess soil moisture
• Lack of excess of light
• Lack of oxygen
• Air pollution
• Nutrient deficiencies
• Mineral toxicities
• Soil acidity or alkanitiy (pH)
• Toxicity of pesticides
• Improper agricultural practices

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TOPIC 1 - The introduction History of plant
pathology

• Old testament blast and mildew mentioned.
• Theophrastus (370-286 B.C.) First one wrote
  about diseases of trees, cereals, legumes.
• Next 2000 years, Nothing was added though many
  writings by historians existed.
• Then, compound microscope in the middle of 17th
  century.

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TOPIC 1 - The introduction History of plant
pathology

• Fungi
• 1755, Tillet studied black dust of bunt. Showed
  bunt appeared in dusty seed more. He considered
  it a poisonous substance rather than living
  microorganisms.
• 1807 Povost Bunt caused a fungi. Studied
  spores, production, germination. Controlled
  dipping the seed in a copper sulfate.
• 1840s Late blight of potato in Ireland caused
  death of hundreds of thousands and imigrate many
  to the USA.
• Debary (1861) showed experimentally that late
  blight caused by Phytopthora infestans, a fungus.
  
• See potatoe famine (cards, films, cartoons) -

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TOPIC 1 - The introduction History of plant
pathology

• 1840s Late blight of potato in Ireland caused
  death of hundreds of thousands and imigrate many
  to the USA.

The Great Irish Potato Famine of the 1840s is
now recognized as the worst human disaster of
19th century Europe. In 1841 the population of
Ireland was 8.5 million people. By 1850, at least
one million died in terrible conditions. Another
million emigrated as refugees. Irelands 1845
Potato Blight is often credited with launching a
wave of Irish immigration to America. The fungus
which decimated potato crops created a
devastating famine. Starvation plagued Ireland,
and within five years, a million Irish were dead
while half a million had arrived in America to
start a new life. CHANGED THE FUTURE OF A
SOCIETY !!
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TOPIC 1 - The introduction History of plant
pathology

• Fungi
• 1878 Millardet Use of Bordeaux mixture
  copper sulfate and lime mix- to control the
  downy mildew of grape. Bordeaux mixture is a
  common pesticide. Asprin of plants !
• Bacteria
• 1876 Pasteur and Koch animal disease antrax as
  a bacterial one.
• 1878 Burril Fire blight on apple / pear a
  bacterium caused one.
• Nematodes 1743 Needham reported first in wheat
  galls (kernels). wheat seed gall nematode.

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TOPIC 1 - The introduction History of plant
pathology

• Viruses 1886 Mayer produced tobacco mosaic by
  injection juice from disesased to healthy ones.
• Tobacco mosaic effective on many crops
• Protozoa
• Mycoplasmas
• Viroids
• Rickettslike bacteria.

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TOPIC 1 - The introduction Importance of plant
diseases

• Kinds and amounts of losses
• 250 000 1 000 000 Irish died in 1845 due to
  Potatoe famine,
• Yr 9, yellow rust, 20-40 yield losses in
  Turkey, 1976, 1990 ???
• Sürak 1593-51, wheat cultivar, in 1976 had 15-20
  grams of 1000 KW compare to 40-45 g of normal
  1000 KW.

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TOPIC 1 - The introduction Importance of plant
diseases

• Kinds and amounts of losses
• Loss of all grape yards due to floksera ?? in the
  USA, Europe, and Turkey
• The great Bengal famine 1943 Brown spot of
  rice. - Helminthosporium oryzae
• Plant diseases alone cause 135 MT loss in
  cereals, 89 in pototoe, 232 in sugar beet etc.

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TOPIC 1 - The introduction Importance of plant
diseases

• Plant diseases could be induced by
• Changes in agricultural production i.e
  Irrigation, more fertilizer, dwarf wheat
  varieties..
• Dwarf wheat varieties Nobel Price to Borlaug,
  higher yield and green revolution in wheat, and
  more diseases, of course.

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TOPIC 1 - The introduction diagnosis of plant
diseases

• Environment vs pathogen
• Easy if typical symptoms are present, even in
  detail sometimes by experts which specific agent
  / factor.
• But a detailed examination / inquiry of
  characteristics needed for a correct diagnosis.

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TOPIC 1 - The introduction diagnosis of plant
diseases

• Infectious diseases
• Pathogens shows symptoms either on the surface or
  inside of the plants.
• Detection and identification
• Naked eye,
• Magnifier
• Microscope

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TOPIC 1 - The introduction diagnosis of plant
diseases

• Diagnosis of various diseasess
• Diseases by parasitic higher plants (Witchweed,
  broomrape)
• The presence is enough.
• Diseases by fungi and Bacteria
• Presence of fungal mycelium or bacterial spores
  means 1)both are the reasons for the diseases, or
  2)both saprophytic fungi or bacteria grow on dead
  tissue because of any other cause.
• Fungi
• Check mycelium, fruting structures, and spores,
  then compare the books of mycology.
• Bacteria
• Check the symptoms of the diseases.
• The surest way production of pure colony, and
  using single colony to infect susceptible host.

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TOPIC 1 - The introduction diagnosis of plant
diseases

• Diseases by viruses, viroids, mycoplasmas,
  ricketsalike bacteria and protozoa
• Difficult
• Small
• Symptoms are nonspecific and resemble those by
  environmental ones, insect induced ones, and
  root diseases.
• First, one has to know whether it is a pathogen
  or not, by transfering it to a healthy plant.
• Any budding, grafting indicate rickettsalike
  bacteria, protozoa,
• By vectors, sap, nematodes indicate virus or
  viroid.
• Further diagnosis
• Inoculate by known pathogens and the pathogen in
  hand, and compare the symptoms,
• Electron microscopy to compare pathogens known
  and in hand,
• Apply certain antibiotics for some agents
  penicillin susceptibility indicates a
  rickettsalike bacterium etiology.
• Thermoterapy (water or air) recovery in shorter
  periods or lower periods indicate rickettsalike,
  opposite, suggest viral etiology.

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TOPIC 1 - The introduction diagnosis of plant
diseases

• Noninfectious Diseases
• If not pathogen exist or found then the reason
  for the diseases is nonliving, environmental
  factor abiotic factor.
• Excess or limitations of water, nutrients (macro,
  micro), CO2, or light.
• Diagnosis
• Check to see if there is any sudden change in
  environmental conditions flood, late / early
  frost, or even drought,
• Each case with a disease is case specific. Use
  your knowledge to diagnose the disease of now.

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TOPIC 1 - The introductionIdentification of a
previously unknown diseases Kochs postulates

• Kochs postulates
• The pathogen must be found associated with the
  disease in all the diseased plants examined.
• The pathogen must be isolated and grown in pure
  culture on nutrient media, and its
  characteristics described (non-obligate) or on a
  susceptible host plant (obligate), and its
  appearance and effects recorded.
• The pathogen from pure culture must be inoculated
  on healthy plants of the same species or variety
  on which the disease appears, and it must produce
  the same disease on the inoculated plants.
• The pathogen must be isolated in pure culture
  again and its characteristics must be exactly
  like those observed in step 2.

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TOPIC 2 Parasitism and disease development
Parasitism and pathogenicity

• Parasite An organism lives and feeds on or in
  other organism.
• Parasitism The relationship between parasite and
  its host.
• Removal of nutrients and water causes reduced
  efficiency, development, and reproduction in the
  host.
• Parasitism, therefore, associated with
  pathogenicity.
• Benefical exceptions root nodule bacteria of
  legume and mycorrhizal infection of feeder roots
  of floering plants, both benefical to each
  others development and this is called symbiosis.
• The damage in diseased plants is more than
  removing of nutirents or water from the host. The
  damage increases 1) secretion of substances by
  the parasite, 2)response of host to the stimuli
  originating in the parasite.
• The result of these in tissues increased
  respiration, disintegration or collapse of cells,
  wilting, abscission, abnormal cell division and
  enlargement, degeneration of specific components
  such as chlorophyill.
• Some organisms but not all are parasitizing
  organisms. Those Fungi, bacteria, mycoplasms,
  rickettslike bacteria, and parasitic plants
  higher plants, viruses, and viroids.

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TOPIC 2 Parasitism and disease development
Parasitism and pathogenicity

• The success of parasite depend on invade,
  proliferate in it, and withstand the conditions
  of host.
• Some parasites (viruses, viroids, mycoplasmas,
  rickettslike bacteria, nematodes, protozoa, and
  fungi of downy mildew, mildew, rusts) can grow
  and produce only on living organisms OBLIGATE
  parasites.
• Some other parasites (most fungi and bacteria),
  can live on either living or dead hosts and on
  various nutrient media NONOBLIGATE parasites.

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TOPIC 2 Parasitism and disease development
Parasitism and pathogenicity

• No correlation between the degree of parasitism
  and the severity of diseases it can cause.
• Obligate and nonobligate parasites differ for
  their attacking and procuring their nutrients
  from the hosts
• Nonobligates secrete enzymes to disintegrate /
  kill cell and its components, and then invader
  (pathogen) utilizes the cells of the host. This
  is like Saprophytism of saprophytes.
• All obligate and some nonoblgates, do not kill
  cells in advance, but get their nutrients either
  penetrating or close contacting.
• Parasitism is a common phenomenon, and not always
  desttructive.
• 2500 parasitics of higher plants existing only
  few parasitize others.
• Wheat has 80, apple has 200 diseases.

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TOPIC 2 Parasitism and disease development
Host range of pathogens

• Pathogens differ for their attacking preferences.
  
• Some attack to
• A single species,
• One genus,
• A wide host range, including many taxonomic
  groups of higher plants.
• Some grow on
• Roots,
• Stems,
• Leaves,
• Fleshy fruits or vegetables.
• Some prefer
• Younger / tender seedlings
• Mature tissues.

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TOPIC 2 Parasitism and disease development
Host range of pathogens

• Oblgates are very specific since probably both
  parasites and host evolve together.
• Nonobligates parasites usually attack many
  different plants and their parts at varrying age,
  because they depend for their attack on
  nonspecific toxins or enzymes that affect
  substances / processes common in plants.
• A point to think about May a pathogen attack a
  host which was previously immune to it? HOW?

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TOPIC 2 Parasitism and disease development
Stages in the development of disease

• A series / chains of events after each other lead
  to development and perpetutaion of the disease
  and the pathogen called disease cycle.
• Disease cycle sometimes fairly corresponds life
  cycle of the pathogen, and occur mostly
  corresponding growth stages of the host.
• Disease cycle involves the changes in the plant,
  in the plant symptoms, in the pathogens and spans
  either within one growing season and or from to
  the next.
• The Main Events in a disease cycle are
• Inoculation
• Penetration
• Infection
• Growth and reproduction of the pathogen
• Dissemination of the pathogen
• Overwintering / oversummering of the pathogen.

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TOPIC 2 Parasitism and disease development
Stages in the development of disease

• Inoculation
• The contact of a pathogen with a plant.
• The pathogen(s) land on or brought into contact
  with a plant Inoculum
• Inoculum Any part of the pathogen causing the
  infection.
• in fungi mycelium fragments, spores, sclerotia
  (compact mass mycelium)
• in bacteria mycoplasmas, rickettsalike bacteria,
  viruses, viroids,
• in nematodes adult nematodes, nematode larvae,
  or egss.

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TOPIC 2 Parasitism and disease development
Stages in the development of disease

• Types of inoculum
• Primary inoculum is the one survives winter and
  causes original infections in the spring / early
  summer. The more abundant and more closer to the
  crop, the more severe the disease.
• Secondary inoculum is the one produced from
  primary infections and cause secondary
  infections.

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TOPIC 2 Parasitism and disease development
Stages in the development of disease

• Sources of inoculum
• Present right in the plant debris or soil of the
  field,
• Carried by seed, transplants, tubers, or other
  propagative organs,
• Other sources outside the field fields near or
  miles away.
• In many cases, the inoculum survives in perennial
  weeds or alternate hosts during winter / summer
  and becomes ready for the next season.

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TOPIC 2 Parasitism and disease development
Stages in the development of disease

• Sources of inoculum
• Present right in the plant debris or soil of the
  field,
• Carried by seed, transplants, tubers, or other
  propagative organs,
• Other sources outside the field fields near or
  miles away.
• In many cases, the inoculum survives in perennial
  weeds or alternate hosts during winter / summer
  and becomes ready for the next season.

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TOPIC 2 Parasitism and disease development
Stages in the development of disease

• Steps in inoculation
• Landing or arriving of inoculum
• inoculum carried by wind, water, insects, etc.,
• Thus, only, a tiny part lands on susceptible
  hosts,
• Some types of inoculum zoospores and nematodes
  attracted to the host by diffused substances
  from the roots.
• Germination of spores and seeds hatching eggs
• Pathogens could initiate infection during their
  vegetative phase.
• But fungal spores and seeds of higher parasitic
  plants first require humidity of longer periods
  enough to pathogen to penetrate.
• Germinated spores produces a germ tube the
  first part of the mycelium, that penetrates into
  host. Some fungal spores does the penetration by
  other spores produced, basidiospores or
  zoospores. Nematodes eggs require favorable
  conditions in some cases this might be drier
  conditions as happens in Central Anatolia.

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TOPIC 2 Parasitism and disease development
Stages in the development of disease

• Conditons favoring inoculation
• The amount of primary / secondary inoculum,
• The occurrence of longer periods of optimum
  temperature, moisture which favor inoculum
  release,
• The direction of air currencies or windblown
  rain,
• The distance of the incoulum from the host
  plants,
• The density of host plants,
• The number and size of the host plants.

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TOPIC 2 Parasitism and disease development
Stages in the development of disease

• Penetration
• Pathogens penetratae plant surfaces by direct
  penetration, through natural openings, or through
  wounds.

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TOPIC 2 Parasitism and disease development
Stages in the development of disease

• Infection
• The process by which pathogens establish contact
  with the susceptible cells and tisssues of the
  host and procure nutrients from them.
• During infection
• Pathogens grow / multiply in plant tissues and
  invade them
• Discolored, malformed, necrotic areas established
  on the host which are symptoms of the disease.
• Invisible changes together with visible changes
  in the appearance and functions of infected
  plants comprise the symptoms of the disease.
• Symptoms change from the moment they appear till
  the plant die.
• The time between inoculation and disease
  appearance is the incubation period, dependant on
  
• Host-pathogen combination,
• Development stage of the host,
• Temperature / humidity of the environment.

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TOPIC 2 Parasitism and disease development
Stages in the development of disease

• For a successful infection not only a pathogen
  comes into contact with a host but also other
  conditions must also be satisfied.
• A susceptible variety of host to
• the race of the pathogen, at the proper
• stage for the disease,
• Suitable environmental conditions
• Temperature
• Humidity
• Disease occur wherever all three
• factors meet, otherwise no disease
• happens.
• In other words, where host is weak, germ
• exist and the environment is suitable, then,
• the host get diseased as happens in all
• organisms.

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TOPIC 2 Parasitism and disease development
Stages in the development of disease

• Growth and reproduction of the pathogen
• Growth
• pathogens mostly invade and infect tissues by
  growing into them,
• Either producing a small spot, a large infected
  spot, or a general necrosis, till the spread of
  the pathogen stops or the tissue of the host
  dies,
• Reproduction could occur by
• Spores in fungi either sexual or asexual,
• Seeds in parasitic higher plants,
• Fission splitting of one mature individual into
  two smaller individuals in bacteria, mycoplasmas,
  protozoa,
• Eggs in nematodes.
• Though the rate of reproduction varies in
  pathogens but, in all of them, one or a few
  pathogens could produce tremendous (huge) numbers
  of individuals in one season.
• Bacteria double their numbers every 20-30 minutes
  in susceptible host,
• First virus particle occur after several hours of
  infection
• Nematodes lay 300 to 600 eggs and could produce a
  dozen generations per year.
• All depends on the conditions, of course. The
  numbers are under optimum conditions.

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TOPIC 2 Parasitism and disease development
Stages in the development of disease

• Dissemination of the pathogen is through
• Wind,
• Insects,
• Contaminated seeds,
• Infected transplants,
• Animals,
• Farm equipments tractors / plows
• Pruning shears.

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TOPIC 2 Parasitism and disease development
Stages in the development of disease

• Dissemination of rusts
• Yellow rust Yr 9
• Stem rust Ug 99

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TOPIC 2 Parasitism and disease development
Stages in the development of disease

• Overwintering / oversummering of the pathogen.
• Pathogens overwinter survive in cold long
  winters or oversummer survive in hot dry
  summers, regardless of host grows or dormant
  during that time. And get ready for coming
  season.
• Fungi has evolved a great ways to overwinter
• Mycelium or spores in fallen or infected leaves
  of fruit trees,
• overwinters as mycelium or seeds on perennials,
• Scleretia on plant debris.

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TOPIC 3 - How pathogens attack plants

• How pathogens attack plants
• A healthy plant is a community of cells built in
  a fortresslike fashion. In other words, it is too
  difficult to surrender.
• Cellulose in the epidermal cells of roots and in
  the intercellular spaces of leaf parenchyma
  cells,
• A layer of cuticle covering epidermal cells,
• An extra layer of waxes outside of cuticle,
  especially on younger plant parts.
• Pathogens attack plants since evolved to live off
  with the plant and capable of acquiring
  substances from the plants. However, the
  pathogens need to first penetrate outer barriers
  of the plants, then, cell walls, and have the
  substancec transformed and be ready for them to
  utilize. Moreover, plants also produce
  stuructures and chemical substances, which
  interfere with the pathogen.
• In other words, a pathogen has to overcome all
  the obstacles such as
• Pathogen must enter and exist the plant,
• Obtain nutrients from the plants,
• Neutralize defense reactions of the plant.
• In most cases, pathogens suuceed the activities
  by secretions of chemical substances on their
  hosts.
• But, penetration and invasion require a
  mechanical force.

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TOPIC 3 - How pathogens attack plants

• Mechanical forces exerted by pathogens on host
  tissues
• Only some fungi, parasitic higher plants, and
  nematodes apply a mechanical pressure to the
  plant surface.
• The amount of pressure vary with the amount of
  presoftening by pathogenic secretions.
• Fungi and parasitic higher plants first adhere to
  the surface, induced by intermoleculer forces
  developing plant and pathogen because of their
  close contact.
• After contact, the diameter of hypha or radicle
  on the host increases and forms a bulblike
  structure appressorium. Then a penetration
  peg arises and advances into cell wall.
  Penetration occur directly via appressorium or
  haustoria - a single piece of mycelia.
  Penetration is always followed by secretion of
  enziymes (See the pictures of next slide).

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TOPIC 3 - How pathogens attack plants
Germinating conidium attaching to leaf surface.
Appressorium (A) and infection peg (I).
Appressorium (A) infection peg (I) and haustorium
(H).
Hyphae colonizing the host cell.
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TOPIC 3 - How pathogens attack plants

• Chemical weapons of pathogens - 1
• Beside mechanical forces, pathogens mostly uses
  chemical compounds while penetrating plants.
• Thus, pathogenic effects on plants result from
  biochemical reactions between those pathogen
  secreted substances and plants produced ones
  readiliy available or not.
• Main groups those substances are
• Enzymes,
• Toxins,
• Growth regulators,
• Polysaccharides,
• Some are very important (growth regulators in
  crown gall, toxin in the Helminthosporium of
  Victoria oat the only reason of the disease)
  and some not (enzymes in soft rots).
• All pathogens except viruses and viroids could
  produce enzymes, growth regulators,
  polysaccharides and possibly toxins.

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TOPIC 3 - How pathogens attack plants

• Chemical weapons of pathogens 2
• In general, plant pathogenic enzymes disintegrate
  the structural components of host cells, break
  down inert food substances in the cell, or affect
  the protoplast directly and interfere with its
  functioning protoplast.
• ENZYMES large proetein molecules, catalyzing all
  interrelated reactions in a living cell.
• A different enzyme for each reaction

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TOPIC 3 - How pathogens attack plants

• Chemical weapons of pathogens 3
• ENZYMATIC DEGRADATION OF CELL WALL SUBSTANCES
• Pathogen first meet the host on a plant surface,
  consisting either cellulose of epidermal cell
  walls, or cellulose plus cuticle of aerial plant
  parts. Cuticle is mostly covered by a wax outside
  of it.
• Cuticular wax as granular or rodlike
  projections or continous layers no report yet if
  any enzyme by a pathogen to degrade it only
  mechanically penetratable by fungi and parasitic
  higher plants (PHPs).
• Cutin main component of cuticular layer, upper
  parts admixed with waxes, and lower parts admixed
  with pectin and cellulolose. Some fungi could
  breakdown cutin via cutinases.
• Pectic Substances the main component of middle
  lamella cement of cells holding them in tissues
  and a large part of primary cell wall Pectic
  substances are polysacharides many enzymes,
  pectinases break down pectic substances.
  Pectinases involved in many diseases production.

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TOPIC 3 - How pathogens attack plants

• Chemical weapons of pathogens 4
• Cellulose a polysacharide, but with chains of
  glucose molecules. The skelatal of cell walls in
  higher plants as microfibrils iron bars of
  concrete building. Many enzymes by pathogens of
  fungi, bacteria, nematodes, PHPs could degrada
  cellulose. The breakdwon of cellulose finally
  produces glucose, carried out by cellulases.
• Lignin exists in the middle of lamella and cell
  wall of xylem vessels and the fibers. Also in
  epidermal and hypodermal cell walls. Lignin is
  phenypropanoid more resistant to enzymatic
  degradation than any substance. The amount of
  lignin degradation is enormous, decomposition of
  all annual and perennial plants in nature. 500
  fungus decompose wood, one-fourth cause
  degradation of lignin.

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TOPIC 3 - How pathogens attack plants

• Chemical weapons of pathogens 5
• TOXINS
• Many interdependent biochemical reactions occur
  in one way or the other. Disturbance of these
  reactions cause disruption of live processes,
  lead to disease development and damage in host.
  Common disturbing agents are toxins, mostly
  produced by pathogens. Toxins act on
  protoplasts and damage or kill cells of plants.
  Some toxins are specific while some effect a wide
  range general of families.
• Toxins with a wide range
• The wildfire toxin or tabtoxin of tobacco caused
  by Pseudomonos tabaci necrotic yellow spots on
  leaves, sterile culture filtrates produce
  symptoms not only on tobacco but also on other
  plants.
• Alternaria spp., Aspergillus, Fusarium spp., and
  Penicillium, causing black point on wheat
  kernels, may produce toxic substance even to
  human. The upper limit as 5 for seeds in silos
  in Australia (Rees et al., 1984 Lehmensiek et
  al., 2004). Politic debates few years ago in
  Turkey.

55
TOPIC 3 - How pathogens attack plants

• Chemical weapons of pathogens 6
• TOXINS
• Host-specific toxins
• Victorin Produced by H. victoriae on oats,
  affects plants from a distance and causes leaf
  blight,
• Periconia circinata toxin by a fungus on sorghum
  roots and lower parts with a scalded appearance
  like oil spots on leaves,
• Alternaria kikuchiana toxin by black spot
  diseases of Japanase pears ) Pyrus serotina,
  susceptible pears are harmed by the filtrate of
  cultures.

56
TOPIC 3 - How pathogens attack plants

• Chemical weapons of pathogens 7
• GROWTH REGULATORS IN PLANT DISEASE
• Plant growth regulated by small number of
  hormones growth regulators. These are
• Auxins Naturally occur in plants as
  indole-3-asetic acid (IAA), moves from young
  tissues to older ones, and destroyed by
  indole-3-asetic acid oxidase and thus IAA is in
  low concentration. IAA leads cell elongation,
  increase membrane permeability, and respiration,
  and promotes synthesi of m-RNA, and protein.
• Gibberellins Normally found in green plants and
  also produced by many microorganisms. The first
  synthesis was from Gibberella fujikuroi, a rice
  disease foolish seedling diseasese. Gibberellic
  acid is a common one. Spraying plants of virus,
  or mycoplasma infected plants, with gibberellin
  reduces some symptoms.
• Cytokinins Necessary for cell growth and
  differentitaion, and inhbit breakdown of proteins
  and nucleic acids, and, thus, inhibit the
  senescence. It occur low in green plants, seeds,
  sap stream.
• Ethylene Lead leaf abscission, fruit ripening.
• Polysaccharides Mucilaginous coat fungi,
  bacteria, nematodes, etc, induce wilt diseases by
  mechanically blocking vascular bundles.

57
TOPIC 4 - Pathogen effects on plant physiological
functions

• Effect of pathogens on photosynthesis
• Effect of pathogens on translocation of water and
  nutrients in the host plant
• Effect of pathogens on host plant respiration

58
TOPIC 4 - Pathogen effects on plant physiological
functions

• Effect of pathogens on photosynthesis
• Photosynthesis
• a basic function of green plants, enabling
  transformation of light energy into chemical one,
  to utilize in cell activities,
• Ultimate sources of all energy used in plant or
  animal,
• Produce energy for all other activities but
  itself.
• Photosynthesis
• light
• 6 CO2 6H2O -? C6H12O6 6 02 chlorophyl

59
TOPIC 4 - Pathogen effects on plant physiological
functions

• Effect of pathogens on photosynthesis
• Photosynthesis
• a basic function of green plants, enabling
  transformation of light energy into chemical one,
  to utilize in cell activities,
• Ultimate sources of all energy used in plant or
  animal,
• Produce energy for all other activities but
  itself.
• Photosynthesis
• light
• 6 CO2 6H2O C6H12O6 6 02
• chlorophyl
• Assumed that photosynthesis has a significant
  role in plants life, then any disturbance of
  photosynthesis by pathogens would result A
  DISEASED condition in plant.
• Result is Chlorosis, necrosis on leafs and
  reduced growth, fruit, etc.

60
TOPIC 4 - Pathogen effects on plant physiological
functions

• Effect of pathogens on photosynthesis
• Result is Chlorosis, necrosis on leafs and
  reduced growth, fruit, etc.
• Earlier stages The reduction in photosynthesis
  is because of the size for photosynthesis but,
  in later, stages, is for affecting chloroplasts,
  and regenerating them.

Fungi on a tree
61
TOPIC 4 - Pathogen effects on plant physiological
functions

• Effect of pathogens on translocation of water and
  nutrients in the host plant
• Water and organic / inorganic nutrients are a
  must for plants to live.
• Water and inorganic nutrients via xylems from
  roots to leaf veins, and then, into leaf cells.
• Some water and inorganics are used by leaf /
  other cells, and some diffuses to atmospheres,
  via stomota.
• On the contrary, organic nutrients are produced
  in leaf cells, and, translocated downward, mostly
  through phyloem.
• Any disturbance of upward and / or downward
  movement by the pathogen would result in diseased
  conditions.
• The plant parts deny or do not receive the
  materials needed, then, become diseased.

62
TOPIC 4 - Pathogen effects on plant physiological
functions

• INTERFERENCE WITH UPWARD TRANSLOCATION OF WATER
  AND INORGANIC NUTRIENTS
• Pathogens interfere with the translocation of
  water / inorganic nutrients by
• Affecting the intergrity or function of the roots
  and causing decreased absorption of water,
• Growing in the xylem,
• Or, even, interfering with water economy, and
  cause excessive transpiration.
• Effect on water absorbtion
• Many pathogens (fungi of damping fungi,
  rootrotting and bacteria etc.) destruct roots
  before even symptoms appear, and, thus decrease
  water absorbtion by roots.
• Effect of water translocation through the xylem
• Damping off, stem rots, and canker pathogens
  destruct xylem of young plants, induce them to
  collapse. Or production of diseases after xylem
  invaded by Vascular wilt causing agents.
• Effect on transpiration
• With disease, transpiration increses, because of
  destruction of leaf cells, protecting the leaf by
  the cuticle, increase in permeability, and
  dysfunction of stomata.

63
TOPIC 4 - Pathogen effects on plant physiological
functions

• INTERFERENCE WITH THE TRANSLOCATION OF ORGANIC
  NUTRIENTS THROUGH THE PHLOEM
• Organic nutrients produced in leaf cells first
  move through plasmodesmata into adjoining phloem
  elements, then, into phloem sieve tubes again via
  plasmodesmata, and into protoplasm of
  nonphotosynthetic cells for utilization or
  into storage organs for storage. Pathogens
  could be active in any stage. They mostly cause
  increase in photosyntehis products and
  respiration.
• - Mercury Mostly in roots, but plants also could
  accumulate atmospheric mercury in leaves - SEE
  the picture on the right.
• - An environmental factor Still a disease,
  disorder.

64
TOPIC 4 - Pathogen effects on plant physiological
functions

• Effect of pathogens on host plant respiration
• Respiration controlled oxidation (burning) of
  CHs and fatty acids, and liberating energy for
  various cell processes. It has 2 steps
• Degrading glucose to pyruvate either
  glycolytic pathway, or glycolysis, or pentose
  pathway,
• Degradation of pyruvate to CO2, water, and 678.
  000 Calories.
• C6H12O6 6 O2 ? 6 CO2 6 H2O 678 000
  Calories
• The energy could be used for
• Accumulate or mobilize compounds,
• Sythesize proteins, activate enzymes, cell
  growth, division etc.

65
TOPIC 4 - Pathogen effects on plant physiological
functions

• RESPIRATION OF DISEASED PLANTS
• Pathogens increase respiration rate, starting
  just after inoculation, and rises, during the
  multiplication and sporulation of the pathogen.
  Then, declines to or lower than healthy plants.
• In resistant varieties increase rapidly with
  infection but declines fast as well,
• In susceptible varieties increase slowly with
  infection bur remains at maximum for longer
  periods.
• Many other changes are observed beside increased
  respiration.
• Increase in activity or concentration of many
  enzymes
• Increase in phenolic compunds,
• Increase in pentose pathway,
• Increase in fermentation
• The increased respiration in disesaed plants is
  the result of increased metabolism in the plant.
• Diseases, first, stimulate growth, increase
  protoplasmic stream and sythesized, translocated
  and accumulated materials.
• The more ATP is utilized for these activities.
  The more ATP is utilized, the more ADP is
  produced and further stimulates RESPIRATION.
• Or less efficent utilization of ATP energy
  induces respiration exta energy leads extra
  activities in plant and MORE respiration.

66
Plant remnants in Çatalhüyük