This document discusses various techniques for breeding disease resistance in crops. It describes two types of disease resistance: vertical resistance which is controlled by major genes and can be transferred readily between genotypes, and horizontal resistance which is controlled by many minor genes and is more difficult to transfer. It then outlines several methods for breeding for disease resistance, including introduction, selection, hybridization, pedigree selection, backcrossing, bulk selection, and genetic engineering. Examples of crops bred for resistance to specific diseases are also provided.

1. Techniques
in
resistance
breeding
PRAVE E N K U M AR M
2021004O81

2. Disease resistance
A physiological deviation from the normal functioning of the organism (i.e., the crop plant)
caused by pathogenic organisms is a disease and may be caused by fungi, bacteria or
viruses.
The inherent ability of an organism (i.e., the crop plant) to resist or withstand the pathogen
is called resistance.
Disease resistance commonly met with in the plant kingdom relative in nature, total
immunity being too rare. Its hereditary transmission from parent to off-spring is essentially
"Mendalian", but often polygenic.

3. TYPES OF DISEASE RESISTANCE
Vertical resistance:
Controlled by major genes (one or two).
Genes are readily transferred from one genotype to another
Presence of genes can be determined by exposing plants to
particular races.
Example:
Leaf Rust Resistance in Wheat

4.  Horizontal resistance:
 Controlled by many genes each with minor effects
 Can control a broad range of races due to the fact that many loci are involved
 Difficult to transfer resistance from one genotype to another
 Individual genes harder to identify
 Example:
 Fusarium Head Blight in Wheat

5. Methods of breeding for disease Resistance
1. Introduction
2. Selection
3. Hybridization
4. Pedigree method
5. Backcross method
6. Bulk method
7. Genetic engineering

6. INTRODUCTION
It is a very simple and inexpensive method.
Varieties resistant to a particular disease elsewhere are proposed to be introduced.
It is possible that a variety resistant in one regained not be resistant in another region due to
variation in the physiological race of the pathogen or due to a much different agroclimatic
condition in the new location.
EX: Ridley wheat introduced fromAustralia has been useful as a rust resistant variety.
 Kalyan Sona and Sonalika wheat varieties introduced from CIMMYT, Mexico and were rust
resistant.
Manila, a rice variety introduced in Karnataka from the Philippines, has tolerance to blast,
bacterial leaf blight and sheath blight.

7. SELECTION
 This is better method than introduction and has more chances of success in obtaining
disease-resistant plants.
 The work of selection is carried outeither in the naturally infected fields under field
conditions or under artificially inoculated conditions.
 The resistance in suchindividuals will occur in nature by mutation.
 Sugandh of Bihar is a selection from Basmati rice of Orissa tolerant to bacterial leaf blight.
 MCU 1 cotton, a selection from Co 4, is resistantto bacterial disease.
 Kufri Red, a potato selection from Darjeeling Red Round is a disease resistant variety.

8. Hybridization (Back cross method)
 Interspecific hybridization is made to transfer the gene or genes for resistance to thecultivated
species.
 Resistance to grassy stunt virus from Oryza nivara to O.sativa, late blight resistance from
Solanum demissum to cultivated potato, rust resistance from durum to aestivum wheat are
some of the examples involving interspecific hybridization.
 The progeny resemble the cultivated parent, then they are selfed and segregating progeny
screened for disease resistance.

9. Conventional methods.
First we screen the germplasm for the source of resistance.
Then we carryout the artificial hybridization of the high yielding crop varieties with these
disease resistant varieties.
The progenies are selected and evaluated for high yield and disease resistance.
Then the progenies are tested and released as new varieties.
-Ex: Himgiri:- disease resistance against leaf rust.

10. Mutation breeding
In this methods physicals agents are used like chemicals, gamma radiations etc.
Since these changes are heritable, the plants with desired charecters are then selected and
used as a source in breeding of new plants. This type of breeding is known as mutation
breeding.
-Ex: in Mung bean resistance to yellow mosaic virus is done by mutation breeding.

12. Crop
Examples
Rice
Krishna, Sarbarmati, Ratna, Padma, Jaya, Bala, Kaveri
Wheat
HD 2281, HD2285,HD2380, ND 2402, Janak, Pratp, Raj 2535
Cotton
LH 900, LH 1556, F 846, F 1054, F 1378, HS 6, Vikas, Sharda, MCU 9, MCU 11, LRA 5166
Pigeon pea
T 21, Prabhat
Green gram
T2, T 44, T51, Sheela
Chickpea
T1, T2, T3, T5, Radhey
Pea
Pant Matar 2, Jawahar Matar 1, Jawakar Matar 4

13. Bulk Method:
Bulk population method of breeding in self-pollinated crop is also known as mass method or
population method of breeding. It was first used by Nilsson Ehle in 1908. It refers to a
species is grown in bulk plot (from F1 to F5 ) with or without selection, a part of the bulk
seed is used to grow the next generation and individual plant selection is practiced in F6 or
later generation. In this method duration of bulking may vary from 6-7 to 30 generation.
Application of Bulk Method:
This method is suitable and most convenient for handling the segregating generation of
cereals, smaller millet, grain legume and oilseeds. This may be used for three different
purposes.
i) Isolation of homozygous lines.
ii) Waiting for the opportunity of selection.
iii) Opportunity for natural selection to change the composition of the population..

14. Achievements:
This method has between used in Barley crop for developing some varieties from the crosses
(Allas X Vaughn), like Arival, Beecher, Glacier, etc. In India only one variety "Narendra Rai" has
been developed in Brown Mustard. This method has a limited application in practical plant
breeding.

15. Genetic engineering method
-It is a highly evolved method. Because in this method we can breed the genes of two
different varieties.
Ex: Rx1 gene of maize plant can be breed with rice which leads to the development of
disease resistance against bacterial street disease caused by Xanthomonas oryzae