HOST PLANT RESISTANCE (IMMUNIZATION)

Disease resistance: It is the ability of a plant to overcome completely or in some degree the effect of a pathogen or damaging factor.

Susceptibility: The inability of a plant to resist the effect of a pathogen or other damaging factor.

Advantages of resistant varieties:

1. Resistant varieties can be the most simple, practical, effective and economical method of plant disease management.

2. They not only ensure protection against plant diseases but also save the time, energy and money spent on other measures of control

3. Resistant varieties, if evolved can be the only practical method of control of diseases such as wilts, viral diseases, rusts, etc.

4. They are non-toxic to human beings, animals and wild life and do not pollute the environment

5. They are effective only against the target organisms, whereas, chemical methods are not only effective against target organisms but also effective against non-target organisms.

6. The resistance gene, once introduced, is inherited and therefore permanent at no extra cost.

Disadvantages:

1. Breeding of resistant varieties is a slow and expensive process

2. Resistance of the cultivar may be broken down with the evolution of the pathogen

Types of resistance:

1. Vertical resistance: When a variety is more resistant to some races of the pathogen than others, the resistance is called vertical resistance.

2. Horizontal resistance: When the resistance is uniformly spread against all the races of a pathogen, then it is called horizontal

3. Monogenic resistance: When the defense mechanism is controlled by a single gene pair, it is called monogenic resistance.

4. Oligogenic resistance: when the defense mechanism is governed by a few gene pairs, it is called oligogenic resistance.

5. Polygenic resistance: When the defense mechanism is controlled by many genes or more groups of supplementary genes, it is called polygenic resistance.