Plant Breeding for Disease Resistance

In tropical agricultural regions number of pathogens like fungi, bacteria and viruses cause different diseases to the crop plants and this often results in a significant decrease in crop yield.

 Such diseases can be controlled by various physical, chemical and biological methods but the most effective, cheapest and convenient method is to produce diseaseresistant varieties.

This not only helps in enhancing the food production but also reduces the dependence on use of chemical pesticides.

It has been studied that the resistance to diseases caused by different pests is genetically controlled character.

It is possible to transfer these characters to the susceptible and desirable variety through plant breeding techniques.

The common crop diseases caused

- by fungi are

- brown rust of wheat,

- red rot of sugarcane

- late blight of potato;

 

- by bacteria - black rot of crucifers;

- by viruses - tobacco mosaic, turnip mosaic etc.

 

Methods of breeding for disease resistance:

Breeding is carried out by the conventional breeding techniques of hybridisation and selection or by mutation breeding.

Hybridisation involves similar steps as discussed and these are:-

+ screening germplasm for resistance sources,

+ hybridisation of selected parents,

+ selection and evaluation of hybrids

+ testing and release of new varieties.

Common crop varieties developed by breeding technique of hybridisation and selection for resistance to fungal, bacterial and viral diseases are;

- Himgiri of wheat for the disease - Hill bunt, leaf and stripe rust.

- Pusa shubhra, Pusa snowball K-l of Cauliflower for the disease Curl blight black rot and Black rot.

- Pusa sadabahar of Chilli for the disease leaf curl, chilli mosaic virus.

In different crop varieties and their wild relatives only a limited number of disease resistance genes are present and identified.

Therefore, the conventional breeding often proved to be constrained.

 Some other methods of breeding for disease resistance are; mutation breeding, genetic engineering, etc.

Mutation breeding

Mutation can be defined as sudden and heritable variation which appears in organism due to permanent change in their genotype.

It is a phenomenon in which alternation of base sequences in DNA is caused and it results in changes in the genotype and phenotype of an organism.

Mutations can be induced artificially through chemical or physical factors called Mutagens.

Selection of mutant organism is done for the desirable characters.

Induction of mutation and its utilization in developing desirable traits in an organism is called mutation breeding.

By this method

- resistant varieties of moong beans to yellow mosaic virus and powdery mildew have been developed.