Disease Resistance.ppt is a ppt about disease

It is about disease resistance

1. DISEASE RESISTANCE
It is the ability of the plant to resist / retard /
reduce the attack of a pathogen / disease
Most simple, practical, effective and
economical
It ensure protection against disease and also
save time, energy & money
It is only method for virus / phytoplasma
diseases
Efficient method for soil borne diseases, where
chemical control is expensive & impractical

2. Pathogenicity = Ability of a pathogen to attack a host
= Virulence + Aggressiveness
Virulence is due to the action of one / a few genes
Aggressiveness is polygenically inherited
 A disease is a result of an interaction of genes
governing resistance in the host with those governing
pathogenecity in the pathogen
Gene – for – gene hypothesis – Flor (1942)
For every gene for resistance in the host, there is a
corresponding gene for pathogenecity in the pathogen

3. Types of resistance (Van der Plank, 1960)
Horizontal Resistance
•General resistance / incomplete
resistance
•Race non specific
•It is controlled by polygenes
•It is governed by minor genes
•Resitance is permanent /
durable
•Quantitative
•Low / moderate resistance
Vertical Resistance
•Specific resistance / complete
resistance
•Race specific
•Monogenic
•It is governed by major genes
•Resistance is unstable / not
durable
•Qualitative
•High resistance

4. Mechanism / Nature of resistance
1.Structural Resistance
Waxes / cuticle
 Linseed varieties resistance to Melampsora lini has thick
cuticle
 Old leaves of apple are resistance to scab / powdery mildew
due to its thick cuticle
 Peach varieties having more hairs on cuticle are resistance
to Venturia inaequalis
 Potato varieties with more hairs are resistant to late blight
Cell wall / Endodermis
 Potato varieties resistant to Pythium have more root fibre
 Potato varieties resistance to wart & brown rot have suberin
deposition in endodermis
 Rice varieties resistant to blast have more silica deposition

5. 2. Functional Resistance
Mandarin varieties resistant to X. citri has a broad cuticular ridge
projecting open the stomata
Wheat varieties resistant to rust opens stomata very late in the
morning, the uredospore germinated during night get desiccated
Barley varieties resistant to loose smut have flowers remain open
only for a short period
3. Chemical Resistance
Grape varieties resistant to powdery mildew have less pH
Tomato varieties resistant to ripe rot have less pH
Peanut resistant varieties to leaf spot have more riboflavin
Rust and powdery mildews favour high sugar content
Alternaria & Helminthosporium favours low sugar

6. Toxic principles
Resistance by phenolics like catechol, protocatechuic acid etc.
Ascochyta resistant in grams is by mallic acid
Scab / late blight resistant in potato by chlorogenic acid
Die-back resistant in lime by isopimpinellin
Alternaria & Septoria resistance is by tomatin
Hypersensitivity against leaf spot and virus diseases
Callose deposition provides resistance to powdery mildew resistance
in barley & Cladosporium cucumerinum in cucumber
Lignification provides resistance against take all disease of oats

7. Phytoalexins
Low molecular weight antimicrobial compounds
synthesized and accumulated in infected parts
immediately after infection
Crop Disease Pathogen Phytoalexin
Sweet potatoBlack rotCeratocystis fimbriataIpomeamarone
Pea Brown rotMonilinia fructigenaPisatin
Bean Brown rotM. fructigena Phaseolin /
hydroxyphaseolin
Chillies Fruit rotColletotrichum capsiciCapsidiol
Cotton Wilt Verticillium alboatrumGossypol

8. Methods of breeding for disease resistance
1.Introduction
Rice varities viz., IR20, IR24, IR28, IR 34, IR36 and IR50
2. Selection
Improved white ponni of rice / MCU1 is selection from CO4
3. Crossing and Hybridization
Grassy stunt virus resistance from Oryza nivara to O. sativa
Late blight resistance from Solanum demissum to potato
4. Induced Mutagenesis
MCU10 bacterial blight resistant cotton – subjection of CO4
seeds to gamma rays
5. Tissue culture
Somaclonal variations - is defined as genetic variation observed among
progeny of plants regenerated from somatic cells cultured in vitro

9. Examples for resistant varieties
Crop Disease Resistant varieties
Rice Blast IR20, IR64, CO45, CO47, ASD18, ADT40
BLB IR20, IR28, IR29
Tungro IR20, IR 28, IR50, CO45
Cumbu Downy mildew WCC75, CO7, CO(cu)9, CO9 hybrid
Sugarcane Red rot COC99061, CO86249, COC22, C0 (Si)6
Okra Yellow vein mosaicParbhani kranti
Cotton Bacterial blightMCU10
Red gram Sterility mosaicVR3, BSR1
Blackgram Yellow mosaic VBN1, VBN3, VBN4, VBN 6, VBN 7, VBN8