Plant Pathology

• Phytopathology / Plant Pathology

  Deals with the nature, causes, and control of plant diseases
• Plant disease


  Any malfunctioning of host cells and tissues that results from continuous irritation by a pathogen or an environmental factor and leads to the development of symptoms
• Disease: Abaca bunchy top


  Caused by BBT virus
• Disease: Late blight of potato


  Caused by Phytophthora infestans
• Biotic factors/parasitic agents of plant diseases

  • Parasitic flowering plants
  • Nematodes
  • Fungi
  • Protozoans
  • Mollicutes
  • Bacteria
  • Virus
  • Viroids
• Abiotic factors/non-parasitic agents of plant diseases

  • Temperature
  • Air pollution
  • Lack/excess of water
  • Nutrient deficiencies and toxicity
• Pathogen


  An agent of disease, i.e. living organisms that can cause disease to other organism
• Pathogens


  • Bacteria
  • Fungus
  • Virus
• Parasite


  An organism that wholly or partly depend on another organism for its food. Most parasites are pathogen.
• Obligate parasite


  An organism that is restricted to subsist on living organisms and attacks only living tissues
• Facultative parasite


  An organism that has ability to be a parasite although it is originally ordinarily a saprophyte
• Saprophyte


  An organism that lives on dead organic or inorganic matter
• Host/Suscept


  The plant that is under the attack of the pathogen
• Symptom


  The outward manifestation or expression of the disease
• Signs


  Typically detectable through observation or laboratory analysis
• Primary symptoms


  The immediate and direct results on the invaded tissues
• Necrotic symptoms


  Death of the protoplast, cells or tissues
• Secondary symptoms


  The effects on the distant and uninvaded plant parts
• Disease: Citrus canker


  Symptom: Canker
• Disease: Corn leaf blight


  Symptom: Blight
• Hypoplastic symptoms


  Inhibition or failure in the differentiation or development of some aspect of plant growth
• Disease: Tungro


  Symptoms: Chlorosis and stunting
• Hyperplastic symptoms


  Abnormal, excessive cell proliferation or tissue growth, often induced by pathogens or hormonal imbalances
• Disease: Corn smut


  Symptom: Kernel enlargement
• Types of overdevelopment


  • Hypertrophy: Increase in size of cells
  • Hyperplasia: Abnormal increase in the number of cells
• Disease: Root galls of eggplant

  Symptom: Gall formation
• Disease: Crown gall of gladiolus


  Symptom: Gall formation
• Specific symptoms


  • Abscission
  • Blast
  • Blight
  • Canker
  • Chlorosis
  • Curling
  • Damping-off
  • Flecks
  • Mosaic
  • Rosetting
  • Rotting
  • Scab
  • Shot-hole
• Virus


  A small infectious agent that replicates only inside the living cells of other organisms. It is a nucleoprotein particle containing either DNA or RNA as its nucleic acid and a protein coat surrounding its nucleic acid. It produces proteins during its replication.
• Viroid


  Infectious particles smaller than any of the known viruses, serving as an agent of a certain plant disease. They are RNA particles smaller than viruses, containing RNA as their nucleic acids, do not contain protein coat, and do not produce protein during their replication.
• Fungi


  • Small, generally microscopic, eukaryotic, usually filamentous, branched, spore-bearing organisms that lack chlorophyll
  • Have cell walls that contain chitin and glucans (but no cellulose) as the skeletal components
  • These are embedded in a matrix of polysaccharides and glycoproteins
• Oomycota


  • Fungal-like organisms, until about 1990 were considered to be true fungi
  • Have cell walls composed of glucans and small amounts of cellulose, but no chitin
• The Oomycota are now members of the kingdom Chromista rather than Fungi but continue to be treated as fungi because of their many other similarities to them, at least in the way they cause disease in plants
• Types of fungi based on their relationship with plants

  • Strictly saprophytic (live on dead organic matter, which they help decompose)
  • Cause diseases in humans (about 50 species)
  • Cause diseases in animals (about as many as cause diseases in humans, most of them superficial diseases of the skin or its appendages)
  • Can cause disease in plants (more than 10,000 species)
  • Obligate parasites or Biotrophs (can grow and multiply only by remaining, during their entire life, in association with their host plants)
  • Nonobligate parasites (require a host plant for part of their life cycles but can complete their cycles on dead organic matter, or they can grow and multiply on dead organic matter as well as on living plants)
  • Facultative saprophytes (primarily parasites)
  • Facultative parasites (primarily saprophytes)