the presentation deals with both conventional and marker assisted breeding methods. It gives an idea as a whole.

2. CHAIRMAN - Dr.J.Gokulakrishnan
Asst.Professor, Dept.of Genetics & Plant Breeding
MEMBERS - Dr.S.Ezhil kumar
Asst.Professor, Dept.of Genetics & Plant Breeding
- Dr.K.Sha
Asst.Professor, Dept.of Horticulture

4. Aim: To control important crop pests and diseases.
Types of genetic resistance:
1. Quantitative resistance – “Horizontal”
2. Qualitative resistance – “Vertical”

5.  Controlled by many genes with minor or additive effects.
Advantages:
 Can control a broad range of races due to the fact that many loci are
involved.
Disadvantages:
 Difficult to transfer resistance from one genotype to another.
 Individual genes harder to identify

6.  Controlled by major genes (one or two)
Advantages:
 Easier screening
 Easier transfer of genes “all or nothing”
Disadvantages:
 Vulnerability to new races
 Continous use of particular cultivar may lead to development of new
race or shift in pest population.

7.  Resistance: No establishment of pathogen in/on the host, or a limited
establishment.
 Tolerance: The host develops, continues to grow, and produces well
despite the pathogen’s presence

8.  It is an abnormal condition in an organism produced by an organism or
an environmental factor.
 “Physiological disorder or structural abnormality that is deleterious to
the plant or to any of its part or products, or that reduces their economic
value.” (Stakman and Harrar, 1957)
 “Harmful deviation from normal functioning of physiological processes.”
(Anon, 1950)

9.  Sorghum downy mildew:
Causal organism: Perenosclerospora sorghi.

10.  Bacterial Stalk Rot:
Causal organism: Erwinia carotovora, Erwinia chrysanthem

11.  Charcoal-Rot:
Causal organism: Macrophamina phaseolina

12.  Southern leaf blight
Causal organism: Helminthosporium maydis
 Maize rust
Causal organism: Puccinia sorghii

13. 1. Disease reduce biomass and hence yield. This may happen in either
of the following ways:
 Killing of plants (vascular wilts)
 General stunting caused by metabolic disruption
 Killing of branches
 Damage to leaf tissues (rusts, leaf blights)
 Damage to reproductive organs including fruits and seeds.
2. Often the loss due to diseases may range from a few to 20 or 30%; in
case of severe infection, the total crop may be lost (Jayaraj. 2002).

14.  Theophrastus (3rd century BC): cultivated variety differed in their ability
to avoid diseases.
 Benedict Prevost: Diseases are produced by pathogen. He showed that
wheat bunt was produced by fungus.
 Andrew knight(mid 19th century): Crop varieties differed for disease
resistance.
 Biffen (1905): Resistance to yellow rust in wheat was governed by a
recessive gene segregating in the ratio 3:1 in F2
 Barrus (1911): Different isolates of a microorganism differed in their
ability to attack different varieties of the same host species; this finding
is the basis for physiological races or pathotypes.
 Flor (1956): Gene for gene hypothesis.

16. Various reactions of hosts to the pathogen may be grouped into;
 Susceptible: Disease development is profuse & is presumably not
checked by host genotype.
 Immune: Host does not show symptoms of a disease(100% freedom
from infection)
 Resistance: Less disease than that in susceptible
 Tolerant: A tolerant cultivar is one which endures disease attack
(R.M.Caldwell et al. 1958) & looks like susceptible one

18. 1. Mechanical
2. Hypersensitivity
3. Nutritional
Mechanical:
 Certain mechanical or anatomical features of host may prevent
infection.
e.g. Closed flowering habit of wheat & barley prevents infection by
spores of ovary infecting fungi (Macor, 1960).

19. Hypersensitivity:
 Found in biotrophic or obligate parasite (e.g. C.O. Of rust, smut etc)
 Immediately after infection several host cells surrounding the point of
infection die leading to death of pathogen or prevents spore production.
 Hypersensitive cell produce chemical/ phenolic compounds
(phytoalaxins) which are fungitoxic & autotoxic (Deverall 1976)
 In large number of cases, resistant reaction is due to hypersensitive
reaction of host.
Nutritional:
 The reduction in growth & in spore production is generally supposed
to be due to an unfavourable physiological conditions within the host.

20. • Postulated by Flor in 1956 based on his work on Linseed rust (c.o.
Melampsora lini)
• For each resistance gene (R gene) in the host, there is corresponding
avirulence genes (avr genes) in the pathogen.

21.  Incompatability reaction
Resistance gene Virulence gene
A a
R Resistance Susceptible
r Susceptible Susceptible

22.  Compatability reaction
Resistance gene Virulence gene
A a
R Resistance Resistance
r Resistance Susceptible

23. A. A known variety
B. Germplasm collection
C. Related species
D. Mutations
E. Somaclonal variations
F. Transgenes

24.  Introduction
 Selection
 Mutation
 Hybridization
 QTL mapping & MAB
 Somaclonal variation
 Genetic engineering
Traditional methods
Biotechnological tools

25. 1. Pedigree method:
 This method is suited for breeding for horizontal resistance.
 Combining disease resistance and some other desirable characters
of one variety with the superior characteristics of another variety.

27. 2. Backcross method:
 Transfer of disease resistance from an agronomically undesirable
variety to a susceptible but desirable variety.
 The backcross would differ depending upon whether the allele for
resistance is dominant or recessive.

29. Single marker analysis & Interval mapping

31. Principle:
It is an approach that has been developed to avoid problems connected
with conventional plant breeding by changing the selection criteria from
selection of phenotypes towards selection of gene that control traits of
interest.
There are three types of selection involved;
 Foreground selection
 Background selection
 Recombinant selection

32.  Used to identify the desirable trait loci.
 Selection using multiple markers for
multiple resistance is useful for
resistance breeding.

33.  It involves selecting BC progeny with
the greatest proportion of recurrent
parent genome.
 Markers used are unlinked to the target
gene/QTL on all other chromosomes

34.  It involves selecting BC progeny with the
target gene and recombination events
between the target locus and linked
flanking markers.

36. Pest is a destructive insect or other animal that attacks crops, food,
livestock etc..
 Insect resistance:
Those heritable characteristics possessed by the plant, which
influence the ultimate degree of damage done by insects - Maxwell et
al.(1972).

37.  Non preference (Antixenosis):
The response of the insect to the characteristics of the host plant
which make it unattractive to the insect for feeding, oviposition or
shelter. It may be due to physical nature or chemical composition of
such plants.
 Antibiosis:
Adverse effects on the insects life history which result when the
insect uses a resistant variety of the host plant or species for food.
 Tolerance:
The ability of the host plant to withstand the insect attack and grow
satisfactorily inspite of the attack by rapidly repairing the damage or by
quick development of tillers, roots etc.

38. CROP INSECT PEST CAUSE OF
RESISTANCE
MECHANISM OF
RESISTANCE
MAIZE
European corn borer
(1st brood)
DIMBOA content in
leaves
Antibiosis
Maize stem borer High aspartic acid, low
nitrogen & sugar
Antibiosis
Corn earworm Toughness of husk,
lack of hair
Non preference
Corn leaf aphid Low hydroxamic acid Non preference &
Antibiosis

39. Ostrinia nubilalis
Rhopalosiphum maidisHelicoverpa zea
Chilo partellus

40.  An effective method against corn
borer.
 BT corn has built in protection, it
possess Cry 1Ab gene which
produces cry proteins that affects
pest on feeding.

42.  Breeding for resistance is a continuous process as every pathogen or
pest evolve over time to break the resistance.
 Concept of molecular breeding and transgenic are booming from its
infancy, availing an ocean of methodologies for breeders to work with.
 The delicate relationship between host, pathogen, pests and their
genetic contributions must be studied prior to initiation.
 Maintenance of broad genetic base is as important as developing
varieties with narrow genetic base.
 Maize is considered to be a breeder’s dream crop as it is almost
compatible to a breeder’s imagination, hence finding a durable resistant
source should be a prime objective.