UPLB

• Crop Protection
• Plant Pathology

  From "pathos" (Greek) = suffering, "logos" = to study, Study of the suffering plant (do plants really suffer?)
• Plant Pathology

  • As a science: Understand the nature of plant disease, Cause - etiology of plant disease, Plant-pathogen interaction, Determine factors affecting disease development, Study methods of control or management of diseases
• Plant Pathology

  • As an art: Plant disease diagnosis, Assessment and forecasting, Recommend control measure
• Ultimate objective of Plant Pathology is to control or manage plant diseases so that losses will be brought to a minimum
• Characteristics of Plant Disease

  • A malfunctioning process that results in suffering
  • Generally harmful/detrimental
  • Produces symptoms - histological and morphological abnormalities
  • Caused by an agent
• Vital Processes of Plants Affected by Disease

  • Root absorption
  • Uptake of water and minerals
  • Photosynthesis
  • Respiration
  • Transport of photosynthates
  • Reproduction
• Importance of Plant Diseases

  • Plant diseases endanger food supply
  • Reduce the quantity and quality of plant produce
  • Cause financial losses
  • Limit the kinds of plants and industries in an area
  • Make plants poisonous to humans
  • Increase cost of production due to control measures
• Types of Losses due to Diseases

  • Losses due to reduction in yield
  • Losses due to deterioration during storage, marketing or transport
  • Losses due to reduction in quality
  • Losses from produce contaminated with toxins that cause various disorders and/or death to animals and man
  • Losses due to predisposition of host to attack by other pathogens
  • Losses from increased cost of production and handling
• Pathogen


  Any agent that causes disease especially the biotic or living agent
• Parasite


  An organism that depends wholly or partly on another organism for its food
• Is a pathogen always a parasite?
• Is a parasite always a pathogen?
• Types of Parasites

  • Obligate parasite - subsist on living organisms and attacks only living tissues (e.g. virus, rust fungi, downy mildew fungi)
  • Facultative parasite - an organism, which has the ability to become a parasite but is ordinarily a saprophyte
• Saprophyte


  An organism that lives on dead organic or inorganic matter
• Facultative saprophyte


  Has the ability to become a saprophyte but is ordinarily a parasite
• Host


  The plant that is being attacked by a parasite, a food relationship between the host and the parasite is implied
• Suscept


  A plant that is susceptible to a disease whether or not the pathogen is parasitic
• Pathogenicity

  The capacity of an organism to cause disease
• Pathogenesis


  Refers to a series of events that lead to disease development in the plant
• Virulence


  Refers to the quantitative amount of disease that an isolate (the pathogen) can cause in a group of plants, a characteristic of a pathogen
• Plant Disease Diagnosis


  Identification of diseases based on symptoms and signs
• Symptom

  Manifestation or expression of a plant as a result of a disease
• Sign


  A pathogen or a part of a pathogen found on a host plant
• Types of Symptoms

  • Local symptoms - Expressed as physiological or structural changes in a limited area of the tissues of the host (e.g. spots, cankers)
  • Systemic symptoms - Expressed as the reaction of a greater part of or all of the plants (e.g. dwarfing, wilting, yellowing)
• Primary vs. Secondary Symptoms

  • Primary - the direct result of pathogen activity on the invaded tissues
  • Secondary - the physiological effects on distant and uninvaded organs
• Microscopic vs. Macroscopic Symptoms

  • Microscopic - expressions of disease in cell structure or arrangement that can be studied only under the microscope
  • Macroscopic - expressions of the disease in the plant or in its parts that can be studied with the unaided eye
• Types of Macroscopic Symptoms

  • Pre-necrotic - stage preceding death of cells
  • Necrotic - characteristics of dead cells and tissues
• General Types of Symptoms

  • Necrotic - Involve the death of protoplast (e.g. spot, canker, blight, scorch)
  • Hypoplastic - Inhibition or failure in the differentiation/development of some aspect of plant growth (e.g. stunting, chlorosis, mosaic, curling and rosetting)
  • Hyperplastic - Expressed with the excessive multiplication, enlargement or overdevelopment of plant organs (e.g. prolonged retention of green color, gall formation, scab, knots)
• Types of Hyperplastic Symptoms

  • Hypertrophy - overdevelopment due to the increase in the size of the cells
  • Hyperplasia - abnormal increase in the number of cells
• Signs of Pathogens

  Structures of the pathogen or pathogen itself; may be the result of the interaction between the pathogen and the host (e.g. ooze, odor)
• Examples of Signs


  • Fungal mycelia, conidia, oospores, teliospores, sclerotial bodies, chlamydospores; nematodes; virus particles; seed of phanerogams
• Koch's Postulates

  • Association - the pathogen or signs of the pathogen must be found associated with the disease in all the diseased plants examined
  • Isolation - the pathogen must be isolated and grown in pure culture on nutrient media, and its characteristics described
  • Inoculation - 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
  • Re-isolation - the pathogen must be re-isolated from the inoculated plants and grown once more in pure culture, its characteristics must be exactly like those observed in the previous steps
• Classification of Plant Diseases

  • Affected plant organ
  • Symptoms
  • Type of affected plants
  • Type of pathogen (infectious diseases - biotic agents, non-infectious diseases - abiotic)
• Abiotic Stress or Injury

  Non-living, Not spread from diseased to healthy plants, Non-infectious, Knowledge of environmental factors before and during disease occurrence necessary for correct diagnosis
• Kinds of Abiotic Diseases or Injury or Stresses

  • Injury caused by adverse physical factors (e.g. freezing injury, chilling injury, sun scald, heat necrosis, black heart, light stress)
  • Injury caused by air pollutants (e.g. ozone, peroxyacylnitrates, hydrogen fluoride, ethylene, nitrogen oxide, particulates)
  • Stress caused by mineral deficiencies and mineral excesses
  • Diseases caused by improper agricultural practices
  • Diseases caused by naturally occurring toxic chemicals
• How to Prevent These Stresses or Injuries

  • Avoid the factor
  • Protect the plants
  • Supply the factor
  • Good management of the crop to produce healthy plants
• Parasitic or Biotic Agents of Plant Diseases

  • Viruses and viroids (subcellular entities)
  • Bacteria and phytoplasmas (prokaryotes)
  • Fungi and fungal-like protists
  • Nematodes
  • Parasitic flowering plants
  • Protozoa
  • Others
• Virus

  Ultramicroscopic made up of nucleic acid and a protein coat, Obligate parasites (replicate only in cytoplasm of living hosts), Nucleic acid core (RNA or DNA) - infectious part, Protein coat - provide a protective sheath, facilitate movement, for transmission by vectors
• Transmission and Spread of Viruses

  • Mechanical means
  • Grafting
  • Nematodes
  • Soil-borne fungi and fungal-like organisms
  • Infected vegetative planting materials
  • Infected seeds
  • Mites
  • Insects - Aphids, leafhoppers, plant hoppers, thrips, whiteflies, mealy bugs