Lecture 16 : HOST PLANT RESISTANCE - DEFINITION - TYPES AND
MECHANISMS ECOLOGICAL AND GENETIC RESISTANCE
Host Plant Resistance (HPR)
Definition
“Those characters that enable a plant to avoid, tolerate or recover from attacks of
insects under conditions that would cause greater injury to other plants of the same
species” (Painter, R.H., 1951).
“Those heritable characteristics possessed by the plant which influence the ultimate
degree of damage done by the insect” (Maxwell, F.G., 1972).
Types of Resistance
Ecological Resistance or Pseudo resistance
Apparent resistance resulting from transitory characters in potentially susceptible host
plants due to environmental conditions.
Pseudoresistance may be classified into 3 categories
a. Host evasion
Host may pass through the most susceptible stage quickly or at a time when insects
are less or evade injury by early maturing. This pertains to the whole population of
host plant.
b. Induced Resistance
Increase in resistance temporarily as a result of some changed conditions of plants or
environment such as change in the amount of water or nutrient status of soil
c. Escape
Absence of infestation or injury to host plant due to transitory process like incomplete
infestation. This pertains to few individuals of host.
Genetic Resistance
A. Based on number of genes
- Monogenic resistance: Controlled by single gene
Easy to incorporate into plants by breeding
Easy to break also
- Oligogenic resistance: Controlled by few genes
- Polygenic resistance: Controlled by many genes
- Major gene resistance: Controlled by one or few major genes (vertical resistance)
- Minor gene resistance: Controlled by many minor genes. The cumulative effect
of minor genes is called adult resistance or mature resistance or field resistance.
Also called horizontal resistance
B. Based on biotype reaction
- Vertical resistance: Effective against specific biotypes (specific resistance)
- Horizontal resistance: Effective against all the known biotypes
(Non specific resistance)
MECHANISMS ECOLOGICAL AND GENETIC RESISTANCE
Host Plant Resistance (HPR)
Definition
“Those characters that enable a plant to avoid, tolerate or recover from attacks of
insects under conditions that would cause greater injury to other plants of the same
species” (Painter, R.H., 1951).
“Those heritable characteristics possessed by the plant which influence the ultimate
degree of damage done by the insect” (Maxwell, F.G., 1972).
Types of Resistance
Ecological Resistance or Pseudo resistance
Apparent resistance resulting from transitory characters in potentially susceptible host
plants due to environmental conditions.
Pseudoresistance may be classified into 3 categories
a. Host evasion
Host may pass through the most susceptible stage quickly or at a time when insects
are less or evade injury by early maturing. This pertains to the whole population of
host plant.
b. Induced Resistance
Increase in resistance temporarily as a result of some changed conditions of plants or
environment such as change in the amount of water or nutrient status of soil
c. Escape
Absence of infestation or injury to host plant due to transitory process like incomplete
infestation. This pertains to few individuals of host.
Genetic Resistance
A. Based on number of genes
- Monogenic resistance: Controlled by single gene
Easy to incorporate into plants by breeding
Easy to break also
- Oligogenic resistance: Controlled by few genes
- Polygenic resistance: Controlled by many genes
- Major gene resistance: Controlled by one or few major genes (vertical resistance)
- Minor gene resistance: Controlled by many minor genes. The cumulative effect
of minor genes is called adult resistance or mature resistance or field resistance.
Also called horizontal resistance
B. Based on biotype reaction
- Vertical resistance: Effective against specific biotypes (specific resistance)
- Horizontal resistance: Effective against all the known biotypes
(Non specific resistance)
