Field Guide of Discovery-based Exercises for - Aseanipm ...

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Field Guide of Discovery-based Exercises for Organic Vegetable Production
• Protection. This is achieved through interposing a protective barrier between pest or pathogen
and susceptible plant. One environment-friendly barrier is spraying soap solution in vegetables
to avoid infestation of scale insects or infection of sooty mold.
• Resistance. This refers to development and use of cultivars that can thwart or impede activity
of a pest or pathogen. Generally, resistance can be categorized as vertical or specific resistance,
and horizontal or non-specific resistance. Vertical resistance is usually conferred by one or
a few genes and is effective only against some biotypes of pest or strains of pathogen. Many
genes control horizontal resistance and resistance is evenly spread against all biotypes of pest
or strains of pathogen.
• Therapy. This refers to treatment of plants infested by a pest or infected by a pathogen. An
example of non-chemical therapy is application of heat (hot or moist) to affected area or plant
parts or materials. This inactivates or inhibits a pest in an infested area or a pathogen in an
infected area or plant tissues.
• Avoidance. This tactic alters environment by making it less favorable to growth and development
of a pest or a pathogen. Examples include field sanitation measures such as leaf removal,
and cultural practices, such as changing planting density, date of planting, date of harvesting,
fertilization, liming, and irrigation.
In entomology, the mechanism of plant resistance to reduce insect attack can be categorized into
tolerance, non-preference and antibiosis 217 :
• Tolerance. Plant has the ability to give satisfactory yield in spite of injury levels that would
normally occur in nonresistant plants. The known components in this type of resistance include
plant vigor, ability of plant to compensate growth, and wound healing.
• Non-preference. Refers to inherent plant characteristics that drive insects away from a specific
host plant. In non-preference, normal insect behavior is impaired such that the chance of insect
in using a plant for oviposition, food, or shelter is lessened.
• Antibiosis. Antibiosis had the most deleterious effect on insects and so far the most sought
objective of plant breeders. Antibiosis usually impairs an insect’s metabolic processes and
often involves consumption of plant metabolites. The obvious effects of antibiosis on insects
include the following: death of immatures, reduced growth rate, morphological malformations,
increased mortality in pupal stage, small adults with reduced fecundity and life span,
restlessness, and other abnormal behavior.
217 Javier, P.A. 2009. Personal communication.