CPRT42 (Plant Pathology) Unit 1 , 2 and 3

• Pathogen - any living agent that causes a disease, such as fungus, bacterium or virus
• Parasite - an organism which depends wholly or partly on another living organism for its food, while conferring no benefit in return
• Obligate Parasite - an organism that is restricted to subsist on living organisms and attacks only the living tissues
• Facultative Parasite - an organism that is normally saprophytic but is capable of being parasitic
• Saprophyte - organism that grows on and derives its nourishment from dead organic or inorganic matter
• Host-plant that is being attacked by a parasite
• Suscept - plant that is susceptible or vulnerable to disease whether or not the pathogen is parasitic
• PLANT DISEASE - is an injurious physiological process caused by a continued irritation of a primary causal factor exhibited through abnormal cellular activity and expressed in a pathological condition called symptom.
• Symptom - is the manifestation or expression of the diseased plant.
• Sign - is the manifestation or expression of a disease-causing agent.
• Inoculum - is any part of a pathogen capable of initiating or causing infection.
• Infection - is a process that occurs when the pathogen has become established in the plant tissues and obtains nutrients from the host.
• 1. REQUISITES for DISEASEDisease development requires the presence of:1.Plant (susceptible)2. Pathogen (virulent)3. Environment (favorable)
• Host - age, sex, race, genetic profile, previous diseases, immune status, religion, customs, occupation, marital status, family background
• Environment - temperature, altitude, crowding, housing, neighborhood, water, milk, food, pollution, noise
• Agent - Biologic (bacteria, viral), chemical (poison, alcohol, smoke), physical (trauma, fire), Nutrition (lack, excess)
• Plant Disease Diagnosis is the identification of specific plant disease through its characteristic symptoms and signs including other factors that may be related to the disease process. Correct plant disease diagnosis is necessary for recommending the appropriate control measures.
• Studies and work that require actual proof of pathogenicity

  requires the application of Koch’s Rules of Proof (Koch’s Postulates)
• Robert Koch - The Father of Plant Pathology
• Constant Association - To establish that an organism is the cause of a disease, it must be found in all cases of the disease examined; it must be absent in healthy organisms
• Isolation - The pathogen should be grown in a laboratory to obtain and maintain a pure culture capable of producing the original infection
• Inoculation - The pure culture of the organism must produce the symptoms and signs of the disease when inoculated into a healthy test plant
• Re-isolation - The suspected causal organism must be reisolated in pure culture from the inoculated plant and must be identical to the original organism
• Disease Assessment - gathering of critical information in the amount of disease that is present in a plant or plant population

  - the purpose is to determine the disease severity and prevalence, relate these to yield loss and the farm economy
• Methods of Measuring Plant Diseases:

  1. Percentage of Diseased Plants (Disease Prevalence/Incidence)

  – for wilts, damping-off, root rots, viral diseases
• Methods of Measuring Plant Diseases;

  2. % Disease Severity – for fruit rots, leaf blights, leaf spots
• Methods of Measuring Plant Diseases:

  3. Measuring the diameter/length/width of the lesion

  4. Use of Descriptive Disease Rating Scales
• Forecasting – predicting when a particular disease will occur and how severe it will be so that farmers will be properly guided in making decisions on disease control
• Disease Forecasting Services:

  potato late blight grape downy mildew etc. Europe & US

  Bureau of Plant Industry National Crop Protection Center Phil