Terminologies and Pre-necrotic/Plesionecrotic

• Pathogen – any agent (biotic/ abiotic) that causes a disease
• Parasite – an organism that depends wholly or partly on another living organism for its food
• Obligate parasite – organism that is restricted to subsist on living organisms and attacks only living tissues
• Facultative parasite – organism which can be a parasite although it is ordinarily a saprophyte
• Saprophyte – organism that lives on dead organic or inorganic matter
• Facultative saprophyte – can become a saprophyte but is ordinarily a parasite
• Suscept – organism that is susceptible to a specific disease whether the pathogen is parasitic
• Host – refers to the plant that is being attacked by a parasite
• Pathogenicity – capacity of a pathogen to cause or incite a disease
• Pathogenesis – refers to disease development in plant
• Virulence – refers to the quantitative amount of disease that can isolate of a given pathogen can cause (size/ number of lesions)
• Aggressiveness – measures the rate at which virulence is expressed by a given pathogenic isolate
• Diagnosis – is the identification of specific plant disease through their characteristic symptoms and signs, and other factors related to disease process.
• A. Symptoms of plant diseases:

  - Refers to the expressions by the suscept or host of a pathologic condition by which a plant disease may be distinguished from other plant diseases.
• - Include visible response to infection, such as, increased respiration, increase leaf temperature, etc.
• - Symptoms vary according to the environment, the host variety and the race of the pathogen involved.
• - Different pathogens may cause the formation of identical symptoms
• a. Local – expressed as physiological or structural changes in limited area of the tissue of the host (gall, spots, cankers)
• a. Systemic – expressed as the reaction of a greater part of all the plant (dwarfing, wilting, yellowing)
• Primary – the direct result of pathogen activity on the invaded tissues (swollen “clubbed” in cabbage root)
• a. Secondary – physiological effect on distant and uninvaded organs (wilting of cabbage leaves on a hot weather from clubbed root)
• a. Microscopic/ Histological – expression of disease in cell structure or arrangement that can be studied under a microscope. Examples: abnormality in cell content, structure or arrangement; cell enlargement and vascular discoloration
• a. Macroscopic/ Morphological – expressions of a disease in the plant or in its parts that can be studied and visible to the naked eye
• Pre – necrotic/ Plesionecrotic – stages preceding death of cells; involve protoplasmic disorganization
• 1. Hydrosis – a water – soaked, translucent condition of tissue due to water – moving from cells into the intercellular spaces (late blight lesions on potato leaves, bacterial soft rot)
• 1. Reddening – red or reddish-brown zones in tissues at edge of necrotic areas (Mycosphaerella leaf spot of strawberry)
• 1. Yellowing – loss of green color in normal green tissue due to destruction of chlorophyll (vein clearing in aster yellow)
• 1. Wilting – a flaccid condition of leaves, shoots, or entire plants. Maybe due to an infectious agent or to lack of water. Wilting caused by the latter is often temporary and plant recovers upon the application of enough moisture unless the drought is prolonged and the plant dies. Wilting by an infectious agent often leads to death of the plant unless controlled in time.
• Local

  (gall, spots, cankers)
• Systemic

    (dwarfing, wilting, yellowing)
• Primary

  (swollen “clubbed” in cabbage root)