Plant Resistance mechanism and Factors of plant resistance

Plant Resistance mechanism, Factors responsible for plant resistance/Characteristics of plant resistance

Definition of Plant Resistance 

Resistance of plants in insect is the property that enable a plant to avoid, tolerate or recover  from injury by insect population that cause greater damage to other plants of the same species  under  similar  environmental  conditions.  This  property  generally  drives  from  certain  biochemical or morphological characteristics of plants which so affect the behaviour and the  metabolism of insects as to influence the relative degree of damage caused by these insects.

Plant resistance Mechanism 

Mechanism of host plant resistance are

1. Antixenosis.

2. Antibiosis.

3. Tolerance.

4. Escape mechanism.

1. Antixenosis: When a plant possess characteristics that make it unattractive to insect pest  for oviposition, feeding or shelter. e.g. Aphid resistance in raspberry.

2. Antibiosis: When the host plant adversely affects the bionomics of the insect feeding on it.

3. Tolerance: When the damage to the host is only slight despite its supporting an insect  population of a size sufficient to damage susceptible host severely.

4. Escape mechanism: The crop maturity and incidence do not coincide, therefore the host  plant mature early and escape the incidence. For example, Early maturing cotton varieties  escape pink bollworm infestation which occurs late in the season.

Factors responsible for plant resistance/Characteristics of plant resistance 

A. Physical factors 

1. Morphological factors 

A number of morphological factors are given below

i. Hairiness: Hairiness of leaves may act as various to normal feeding or oviposition of  insects. It is associated with resistance to many insect pest, that is in cotton to jassids and in  turnip to turnip aphid.

ii. Narrowness: Narrowness of the leaves will prevent the oviposition of insects because  narrow leaf is not wide enough to place the abdomen of female insect.

iii. Scent: Disagreeable odour may contribute to non preference of plant to insect.

iv. Colour of plant: Plant colour may contribute non preference in some cases. e.g. Red  cabbage and red leaved Brussels sprout are less preferable than green varieties by butterflies  and certain other lepidoptera for oviposition.

2. Anatomical factors 

Large number of vascular bundle and thick hypodermal layer present mechanical obstruction  to feeding and oviposition and thereby lead to non preference as well as antibiosis. e.g. Thick  leaf lamina in cotton contribute to jassids resistant.

B. Chemical factors 

Several chemical factors are known to be associated with insect resistance in many crop. e.g.  In rice, high silica content in shoots confers resistance to shoot borer as it causes rapid  wearing mandibular mouthparts of these pest. The plants which contain 12­-13% silica are  resistant to chewing type insect.