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 (race-specific resistance,
qualitative resistance, discriminatory resistance). Vertical resistance is usually
governed by single gene and is unstable.
2. Horizontal resistance: When the resistance is uniformly spread against all the races
of a pathogen, then it is called horizontal/generalized/non-specific/field/qualitative
resistance. Horizontal resistance is usually governed by several genes and is more
stable.
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.
