Slide 1: 1 SEMINAR
“BREEDING FOR DISEASE RESISTANCE”
Dr. K.B. Wanjari
Department of Agricultural Botany
Post Graduate Institute, Dr. PDKV, Akola. Slide 2: 2 Abnormal condition in the plant produced by an organism.
“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) What is disease? Slide 3: Agrios, G.N. 1998 Different Pathogens Causing diseases Slide 4: 4 Losses due to diseases
Disease reduce biomass (dry matter) & hence Yield. This may
happen in either of the following ways:
killing of plants (e.g. vascular wilts, various soil borne fungi),
general stunting caused by metabolic distruption, nutrient drain or
root damage (e.g.many viruses),
killing of branches (e.g. some fungal diebacks),
damage to leaf tissues ( e.g. many rusts, mildews, blights, leaf spots),
damage to reproductive organs including fruits & seeds.
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). Slide 5: 5 MAJOR FAMINES OR FOOD LOSSES
The wheatless days (1917’s) in USA, due to stem rust epidemics;
Irish famine (1840’s) due to potato leaf blight epidemics;
Devastation of all Victoria-derived oats (mid 1940’s) in USA due to
fungus causing Victoria blight disease;
Bengal famine (1943’s) due to brown spot (Drechslera oryzae) disease of
Downy mildew epidemic (1973’s) in pearl millet (c.o. Sclerospora
graminicola) in India ; and
Bacterial blight (X.campestris pv.oryzae) (1980’s) severe out-break in
Panjab (A.P.K.Reddy 1980). Important fungal diseases of major crops in India : 6 Important fungal diseases of major crops in India DasGupta et al (2003) Important viral diseases of crops in India : 7 Important viral diseases of crops in India Slide 8: 8 History of breeding for disease resistance
Theophrastus (3RD Century):cultivated variety differed in their ability to avoid
Benedict Prevost: diseases are produced by pathogen. He showed that wheat bunt was
produced by a 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.
Erikson (1894):Pathogens ,although morphologically similar,differed from each other
in their ability to attack different related host species.
Barrus (1911) :different isolates of a microorganism differed in there 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. Slide 9: 9 Agrios, G.N. 1998 Disease Development Slide 10: 10 Stages of disease development (especially fungal diseases):
Contact: landing of pathogen on host tissue
Infection: pathogen gains entry in to the host tissue
Establishment: pathogen proliferates & spreads within host
Development: spore production/multiplication by pathogen &
symptoms developed Slide 11: 11 DISEASE REACTIONS
Various reactions of hosts to the pathogen may be grouped into;
Susceptible: disease development is profuse & is presumably not
checked by host genotype.eg.Agra Local susceptible to wheat rust.
Immune: host does not show symptoms of a disease (100%
freedom from infection), r=0
Resistance :less disease than susceptible, r>0 & r<1
Tolerant: a tolerant cultivar is one which endures disease attack (R.M.Caldwell
et al. 1958 ) & looks susceptible one (Browning & Frey 1969). Slide 12: 12 Vertical & horizontal resistance
Van der Plank (1963,1968) Vertical Resistance
Specific resistance of host to particular race of a pathogen.
Also called oligogenic,race spacific,pathotype specific or specific resistance.
Controlled by one or few major genes.
When controlled by single major gene it is known as monogenic resistance.
Each gene has large & easily identifiable effect on resistance.
Less stable as can be overcome by appearance of one virulent gene.
VR involves hypersensitive reaction to the pathogen.
Less effect of environment.
VR governed by two or more major gene is more durable than controlled by single major gene.
Very effective against few races but totally ineffective against others.
Transfer from one host to other is simple. Slide 13: 13 Horizontal Resistance
Resistance of host to all the races of pathogen.
Reproduction rate of pathogen is never zero,but is less than one,i.e.r>0 but <1.
Also called as race non specific,pathotype non specific, polygenic, partial or
Controlled by polygenes.
Provides protection from all races of a pathogen.
It has continuous variation & hence,impossible to classify plants into different clear-cut classes.
More durable than VR since it involves sevsral features (polygenes) of host plant.
More stable since it require new genes for virulent that is less probable.
Influenced by environmental factors.
Some degree of effectiveness against all races though may not be equally effective against all.
Transfer of HR from one host to another is more difficult than VR. Slide 14: 14 Mechanism of disease resistance
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).
Several leaf characters of rice cultivars viz. rolled, narrow & dark green were
associated with resistance to bacterial leaf blight (X.campestris pv. oryzae)
resistance (C.B.Singh & Y.P.Rao 1971). Slide 15: 15 Hypersensitivity:
Immediately after infection several host cells surrounding the point of infection die leading
to death of pathogen or prevents spore production.
Found in biotrophic or obligate parasite (e.g. C.O. of rust ,smut etc.).
Hypersensitive cell produce chemical/ phenolic compounds (phytoalexins, etc) which are
fungitoxic & autotoxic (Deverall 1976)
In large no. of cases, immune reaction is due to hypersensitive reaction of host.
The reduction in growth & in spore production is generally supposed to be due to an
unfavourable physiological conditions within the host.
Most likely, a resistant host does not fulfill the nutritional requirements of pathogen &
hence limits its growth & reproduction. Slide 16: 16 Gene-for-gene concept:
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 gene) in the
pathogen(Flor, 1956). Slide 17: 17 Genetics of disease resistance in some crop plants D = dominant gene, d = recessive gene, I = inhibitor gene, m = modifier gene Slide 18: 18 Molecular basis for gene-for gene-relationship
On the basis of molecular interactions involved in producing
resistant/susceptible responses in the host, the gene-for-gene
relationship may be classified into two general groups:
Compatible reaction Slide 19: Incompatibility reaction Found in biotrophic pathogens (obligate parasites) (e.g. rusts & smuts) and is
associated with hypersensitive response of the host
Only one of the four combinations would lead to the resistant response since
the products of R & A would recognize & interact with each other.
The product of alleles a & r are unable to recognize each other, & there is no
interaction between them hence reaction of host becomes susceptible. Allele A of the virulence gene specifies avirulence.
Allele a of the virulence gene governs virulence. Slide 20: Compatible reaction Found in heterotrophic pathogens (facultative parasites) e.g. Helmithosprium leaf
blight (of sugarcane & maize),Victoria blight of oats etc.
The allele for resistance of the host ( R) produces a modified /specific substances
,which is unable to recognize & interact with the product (toxin) of alleles for
virulence (a) in the pathogen.
Similarly, the allele for avirulence in pathogen (A) specified modified product
(generally a toxin), which is not able to interact with the product of the alleles of the
susceptibility (r) in the host & due to this reason only one of the fours combinations
would lead to susceptibility and rest lead to resistant. Allele A of the virulence gene specifies avirulence.
Allele a of the virulence gene governs virulence. Slide 21: 21 Sources of disease resistance:
A known variety
Unrelated organisms Slide 22: 22 A known variety /cultivated varieties :
best sources of resistance since they possess good agronomic characters
besides disease resistance.
e.g. Cotton variety MCU 5 VT tolerant to Verticillium wilt was isolated from
commercial variety MCU 5 of G. hirsutum.
Germplasm collection :
Potential sources of resistance in all the cultivated crops.
e.g. In cotton several germplasm lines resistant to bacterial blight & Fusarium
wilt have been identified based on screening of large no. of germplasms in
Generally germplasm lines have poor agronomic characters. Slide 23: 23 Related species/ wild species :
Often resistance to a disease may not be present in the varieties
of the concerned crop species. In such cases, it would be
necessary to transfer resistance genes from related species
through interspecifc hybridization.
Despite many problems (viz. cross incompatibility, hybrid
inviability, hybrid sterility and linkages of several undesirable
traits with desirable ones) in such gene transfers, it has been
successfully and extensively used in many cases. Slide 24: 24 Some of the wild /related species (genera) of different crops used to transfer
or possessing genes for disease resistance. Slide 25: 25 Screening technique
Screening for disease resistance is carried out under field and
The glasshouse tests are conducted under controlled conditions &,
therefore, glasshouse screening is considered more reliable than field
Screening procedure for various types of diseases:
Soil borne diseases
For soil borne diseases like root rots, colar rots, wilts, etc. the screening
is done in disease sick plots.
Disease sick plots are developed in three ways :
by mixing soil from other sick plots
by adding remains of diseased plants, and
by adding inoculum developed in the laboratory.
The soil from disease sick plots can be used in pots for conducting tests in the glass house. Slide 26: 26 Air borne diseases
For air borne diseases viz, rusts, smuts, mildews, blights, leaf spots, etc.,
The screening is done either by dusting the spores or by spraying spore
suspension on healthy plants.
Planting of highly susceptible varieties after few rows of test material is
also used to develop the inoculums.
Seed borne diseases
In case of seed borne disease like smuts and bunts, either dry spores are
dusted on the seeds or the seeds are soaked in the spore suspension.
Insect transmitted diseases
the insect from susceptible varieties are collected and released on healthy
plants or juice of diseased plants is rubbed onto healthy plants after
causing mechanical injury in healthy plants. Slide 27: 27 Methods of breeding for disease resistance
Commonly used breeding methods are:
Tissue Culture Methods:
Somatic Hybridization (Protoplast fusion)
Meristem-tip culture (for virus free planting material)
Genetic engineering (Transgenics) Tradional Methods Biotechnological Tools Slide 28: 28 SELECTION
Cheapest and quickest method
The resistant plants may be multiplied, screened & released as a variety.
Kufri Red, potato from Darjeeling Red Round.
Pusa sawani, bhindi (A.esculentus) from Bihar is resistant to yellow
mosaic under field condition.
MCU1, Cotton (G. hirsutum) from CO-4 for resistance to black arm.
The resistant variety may be introduced & after testing, if found suitable,
can be released in the disease prone area.
Easy & quick
Introduction also serve as source of resistance in breeding programmes. Slide 29: 29 Limitation
Introduced varieties may not perform well in new area.
May become susceptible to concerned disease in the new environment,
May be susceptible to the concerned diseases to other diseases common in the
new area, e.g. Kenya wheats (T. aestivum) introduced in India were rust resistant but
they were highly susceptible to loose smut.
Ridley wheat introduced from Australia has been useful as a rust resistant variety.
Early varieties of groundnut (A. hybpagaea) introduced from USA have been resistant
to leaf spot (tikka) disease (C.O. Cercospora orachidicola).
Kalyan sona & sonalika varieties originated from segregating material introduced
from Mexico, & were rust resistant. Slide 30: 30 Mutations
Induced mutations can be utilized by Direct release as a variety (resistant mutant) & by
utilization in hybridization programme.
e.g. Co 8153, a sugarcane variety developed from variety Co 775 with the use of gamma-ray
irradiation was resistant to smut.
used for (i) transfer of disease resistance from an agronomically undesirable variety to a
susceptible but otherwise desirable variety (by backcross method).
(ii) combining disease resistance & some other desirable characters of one variety with the
superior characteristics of another variety(by pedigree method) Slide 31: 31 Pedigree method
It consists of selecting individual F2 plants for desirable features, including
resistance to diseases.
Progenies of these selections are reselected in each succeeding generation until
homozygosity is obtained.
Artificial epiphytotic conditions are created in early segregating generations for the
selection for disease resistance.
This method is quite suited for breeding for horizontal (polygenic) resistance.
Occasionlly, transgressive segregation of quantitative characters including disease
resistance is encountered.
Achievements: KalyanSona, Sonalika, Malviya 12, Malviya 37, Malviya 206, Malviya 234,
& many wheat varieties.
Laxmi (American Cotton variety) resistant to red leaf blight was developed
through the cross between susceptible parent Gadag1 & the resistant
parent CoimbatoreCombodia2. Slide 32: 32 Backcross methods
When resistance is dominant, F1 is back crossed to the susceptible
The progeny of first backcross generation is tested for resistance.
The resistant plants are again backcrossed to the susceptible
After several generations of backcrossing (5-6), plants with characters
almost identical to the original susceptible variety are obtained with an
added advantage of resistance in them.
When resistance is recessive, the progeny of each back cross
generation is selfed.
At the end of backcross programme, the progeny are selfed &
resistant plants are selected.
Progenies derived from different resistant plants that are identical in
agronomic characteristics are usually bulked to produce the new
disease resistant variety.
The new variety is almost identical to the recurrent parent, except for
disease resistance. Slide 33: 33 Advantages:
1) When resistant variety is unadapted & agronomically undesirable, backcross
method is an obvious choice.
2) Useful to transfer one or few major genes (vertical resistance).
3) Extensive yield trials are usually not required before its release for commercial
4) Multiple resistance breeding is possible.
No advancement in yield potential is possible.
Transfer was the first commercial wheat variety in which rust resistance was
transferred from a related species.
Rust resistance was transferred to Kalyansona from several diverse sources e.g.,
Robin, K1, Bluebird, Tobari, Frecor, HS 19 etc.which resulted in release of three multiline
varieties of wheat, namely, KSML 3, MLKS 11, & KML 7406.
[Source: Dasgupta (1991);Singh (2000)] Slide 34: 34 Marker aided selection:
MAS is potentially useful for breeding for disease resistance in at least four ways:
As a substitute for a disease screen,
To accelerate the return to the genotype of the recurrent parent during backcrossing,
To reduce linkage drag of linked deleterious genes,
To select for disease resistance linkage drag of linked delecterious genes, & to select
for disease resistance QTL.
In this technique, linkages are sought between DNA markers & agronomically important
trait viz., resistance to pathogens etc.
Instead of selecting for a trait the breeder can select for a marker that can be detected
very easily in this selection scheme. Slide 35: 35 MOLECULAR MARKER:
A molecular marker is a DNA sequence that is readily detected and whole inheritance can
easily be monitored.
Molecular marker are used to identify and tag desired gene.
Different markers use for disease resistance are:
RFLP (Restriction fragment length polymorphism )
RAPD (Random amplified polymorphic DNA markers)
SSRT (Simple sequence repeats or microsatellites
AFLP (Amplified fragment length polymorphism)
STS (Sequence Tagged Sites)
SCAR (Sequence Characterised Amplified Region) Slide 36: 36 Some examples of molecular markers associated with resistance traits in crop plants Slide 37: 37 SOMACLONAL VARIATION
"The variability generated by the use of a tissue culture cycle.“
"A tissue culture cycle is a process that involves the establishment of a
dedifferentiated cell or tissue culture under defined conditions, proliferation for a
no. of generations & the subsequent regeneration of plants." (Larkin & Scowcroft, 1981).
Disease resistant somaclonal variants can be obtained in the following two ways:
1) Screening: Plants regenerated from cultured cells or their progeny are
subjected to disease test & resistant plants are isolated.
2) Cell Selection: cultured cells are selected for resistance to the toxin or culture
filterate produced by the pathogen & plants are regenerated from the selected
Cell selection strategy is most likely to be successful in cases where the toxin is
involved in disease development.
Resistance was first reported in sugarcane for eye spot disease (Helminthosporium
sacchari) Slide 38: 38 A] A list of disease resistant crop plants obtained by screening of somaclones at the plant level without in vitro selection. Slide 39: 39 B] Disease resistant crop plants obtained by in vitro selection. Slide 40: 40 Somatic cell hybridization
Involves physical union or fusion of protoplast from two parents.
A technique of fused protoplast from two contrasting genotypes for production of hybrids or cybrids which contain various mixture of nuclear & / or cytoplasmic genomes respectively.
Because of the inherent totipotey of the isolated cell it is possible to regenerate a whole plant out of the fused protoplasts.
Somatic hybrids have been produced between several species such as Arabidopsis thaliang & Brassica compestri, potato & tomato, Nicotiana and Lycopersicon, etc. (Khush & Brar, 1988). Slide 41: 41 Genetic traits transferred via protoplast fusion. (Chawla,1998) Slide 42: 42 MERISTEM TIP CULTURE ( for virus free planting material)
Cultivation of axillary or apical shoot meristems, particularly of shoot apical meristem is
known as meristem culture.
Limmaset & Conuet (1972) observed that in virus infected plants, the virus concentration
decreases towards the growing point.
Morel and Martin (1952) developed the technique of meristem culture for in vivo virus
eradication of Dahlia.
Generally, explants taken for actively growing plants at the beginning of growing season
are the most suitable.
In practice shoot tip of upto 1 micro meter are used when the objective in virus
e.g. Banana free from cucumber mosaic virus, cauliflower free from cauliflower mosaic
virus, pea from seed borne mosaic virus, potatoes free from parasrinkle virus X, S Y, a
leaf roll & spindle tuber virus & sugarcane from mosaic (Siddiq and Sharma 1995).
Also used to develop virus free plants of dahlia, carnation, strawberry, chrysanthemum,
archids, etc. (Khush, 1995). Slide 43: 43 Transgenics for disease resistance
Transfer of genes between plant species has played an important role in crop
improvement for many decades.
Genes expected to confer disease resistance are isolated, cloned &
transferred into the crop in question.
Useful traits viz.,resistance to diseases, insects & pest have been transferred
to crop varieties from noncultivated plants.
The overall process of genetic transformation involves introduction, integration &
expression of foreign gene in the recipient host plant.
Plant that carry additional stably integrated, & expressed foreign genes transferred
(transgenes) from other genetic sources are reffered to as transgenic plants.
The capacity to introduce and express diverse foreign genes in plants was first
described in tobacco by Agrobacterium mediated and vectorless approach (Horsch
et al., 1984.)
A virus resistant transgenic variety of squash is in commercial cultivation in
USA. Slide 44: 44 Virus Resistant Transgenic Plants Slide 45: Transgenic Virus Resistance Papaya plant Virus Susceptible Papaya Plant Slide 46: 46 B] Transgenic Plants (Fungal and Bacterial Diseases) Slide 47: 47 Disease Epidemics
An epidemic is a severe outbreak of disease beginning from a low level of infection.
Epidemics are common in case of air borne fungi.
An epidemic progresses from low infection level.
e.g. An epidemic of potato leaf blight may be initiated by a single infector plant / sq. km.
Causes of Epidemics:
Narrow genetic base of cultivated crops
Large acreages under single varieties
Failure of VR genes (eg. Vertifolia potato variety)
Inadvertent breeding for susceptibility. Slide 48: 48 Measures for Prevention of Epidemics: (Management of Disease Resistance):
Kush (1995) propose four approaches to prolong the useful life of a variety with VR
Deployment of genes over time
Development of genes over space
Pyramiding of vertical genes, and
Multiline varieties Slide 49: 49 Deployment of genes over time
Strong genes for VR may be employed or may be used to check epidemics in
alternate years so that the virulent pathotype against any one of them doesn’t
evolve & doesn’t survive even if it did evolve.
based on the principle of crop rotation to control certain soil borne pathogens.
Deployment of genes over space
Strong genes for VR may be employed or may be used to check epidemics in
different geographical regions; these regions would run perpendicular to the
direction of movement of the pathogen.
Thus each strong gene would act as a sieve for the pathotype virulent on the
succeeding one(s). Slide 50: 50 Gene Pyramiding (Watson & Singh, 1953):
Incorporation of diverse major genes for resistance to a pathogen /
insect in one & the same variety.
It is believed that, greater the no. of major genes for resistance in a
variety greater would be its longevity.
May lead to the evolution of “super races”
If the super race in produced, which may overcome the combined resistance,
then several resistance genes may be simultaneously rendered ineffective &
may lead to quick exhaustion of available genes for resistance (Kush, 1995). Slide 51: 51 Multiline Variety:
One of the breeding approaches for a long-range control of diseases in
SPCs is the development of multiline varieties.
“A multiline variety is a population of plants that is agronomically uniform
heterogenous for genes that condition reaction to a disease”
This concept was first given by Jensen (1952) for use in oats
Similar approach was suggested by Borlaug(1959) in Wheat for controlling
stem rust. Slide 52: 52 Characteristics of a good multiline:
It has genotypic diversity with respect to vertical genes.
Each vertical genotype must be strong enough to ensure that reduction in
the exodemic is maximum.
The multiline should have normal resistance to other important diseases of
concerned crop & area.
The multiline should have phenotypic uniformity with respect to agronomic
characters like plant height, maturity & seed type.
The multiline should have yield advantage to the extent possible. Slide 53: Combines VR and HR
Exploit multiple alleles
Exploit linked genes
Extend life of resistant genes
Exploit genetic diveresity Costly
Breeding grounds for new races
Possibility of super race Advantages Limitations Achievements of Multilines in India : Achievements of Multilines in India Slide 55: 55 Merits of breeding for disease
losses caused by disease crops are minimized with use of
reduction in the cost of production resulting in increasing cost
Reduces environmental pollution & heath hazards by reducing
use of pesticides.
They are non toxic to man, farm animals & wild life (do not
contain pesticidal resistance).
Genetic resistance is only solution of some of the diseases
such as wilts, rusts, smuts, nematodes and bacterial blights. Slide 56: 56 Demerits of breeding for disease
It is long term process which takes 10-15 years to develop agronomically acceptable variety.
In some cases, breeding for resistant to one disease leads to the susceptibility to another pests.
Breeding for disease resistance is an expensive method (requires adequate finance for long period). Slide 57: 57 Breeding achievements for resistance breeding for major field crops Slide 58: 58 Slide 59: 59 Note:-1) Abbreviations used before varieties : T - Tollerent, MT - Moderately tollerent, R - Resistant, MR - Moderately resistant. S - Susceptible
2) Varieties coated as T/MT/MR/R for biotic or abiotic stresses is observed only at the time of their release. Slide 60: 16-60 THANK YOU The hazardous effect of fungicides, bactericides and insecticides, or their degradation products, on the environment and human health strongly necessitates the search for new harmless means of disease control…….and i.e. Development of resistant varieties.