2. • Commonly followed breeding methods are
Selection
Introduction
Mutation
Hybridization
Soma clonal variation
Genetic engineering
3. Selection
• Selection resistant plants from commercial
variety –cheapest and quickest method
• This method has been very useful at past
,present-limited use
• Eg:- Kufri red potato is a disease resistant
selection from “Darjeeling red round
• Eg:-Pusa swani bhindi –yellow mosaic
resistant selection from collections in bihar
4. • Cotton variety MCU 1 –selection from Co -4 –
resistant to Black arm disease
• Other examples
• Resistance to curly top in sugar beet
• Leaf spot and powdery mildew in alfalfa
5. Introduction
• Resistant varieties may be introduced for
cultivation into a new areas .
• simple and quick means of obtaining
resistance
• Disadvantages
• Sometimes introduced var may not perform well.
• May become susceptible to concerned disease in a
new envt.
• They may be susceptible to other races of the
concerned diseases in the new area
6. • Eg:- kenya wheat introduced into India were
rust resistant , but susceptible to loose smut
• Successful examples of introduction are
1. Ridley wheat introduced from Australia is rust resistant
2. Early variety of groundnut introduced from USA –resistant
to tikka disease
7. Mutations
• Resistance to some disease may be obtained through mutations
arising spontaneously or induced .
• Spontaneous –at a low rate in nature
• Induced –artificial , through chemical and physical agents
• Mutagens- agents used
physical –ionising -----alpha, beta ,fast neutrons , thermal
neutrons, x rays, gamma rays
_ non ionising -----ultra violet radiations
chemical –alkaylating agents –EMS, MMS, sulphur mustard
acridine dyes –ethium bromide Acridine yellow
base analogues- 5- bromouracil
8. • Resistance to victoria blight
(Helminthosporium victoriae ) in oats was
induced by irradiation with x-rays
• Other examples are
• Resistance to stripe rust and bunt in wheat.
• Crown rust in oats
• Mildew in barley
• Rust in linseed
9. • Leaf spot and stem rot in peanut
• Rust in soya bean
• Bacterial leaf blight and bunt in rice
• Powdery mildew in mungbean
10. Hybridization
• Most common method of breeding for disease
resistance
• 2 objectives for hybridization –
• Transfer of disease resistance from a agronomically
undesirable variety to a susceptible but other wise
desirable(backcross)
• Combining disease resistance and other desirable characters
of one var with the superior characteristics of another
variety(pedigree)
11. • Back cross method
Useful in transferring genes for resistance
from a var that is undesirable in agronomic
characteristics to a susceptible var which is
agronomicaly desirable and adapted
Generaly 5-6 backcross are made .
At the end of the cross ,progeny are selfed and
resistant plants are selected
The new variety is similar to the recurrent
parent except for disease resistance .
12. Pedigree method
• This method is suited for breeding for
horizontal or polygenic resistance
• Majority of disease resistant commercial
varieties have been developed through this
method
• Eg:- kalyan sona, Sonalika ,malviya 234,
cotton variety like laxmi (resistant to red leaf
blight)
13. Soma clonal variation
• Somaclonal variation is the variation seen in plants that have been
produced by plant tissue culture
• Chromosomal rearrangements are an important source of this
variation.
• This is obtained in two ways
• 1. plants regenerated from cultured cells are subjected to
disease test and resistant plants are isolated
• 2. cultured cells are selected for resistance to the toxin or
culture filtrate produced by the pathogens
• After that plants are regenerated from the selected cells
15. Advantages
• Somaclonal variation leads to the creation of
additional genetic variability.
• Characteristics for which somaclonal mutants can
be enriched during in vitro culture includes
• resistance to disease pathotoxins
• herbicides
• high salt concentration
• mineral toxicity and tolerance to environmental
or chemical stress
• increased production of secondary metabolites.
