Saifullah11-ARID-489

M.Sc Hons Plant pathology

Bacterial virulence and Plant disease

Definition of VirulenceDifferentiation between Virulence and

PathogenisityVirulent proteinsType three secretion systemHypersensitive responseDefinition of diseaseSymptoms

Contents

The ability of a microorganism to invade and cause injury to the host. It is the relative capacity of a microorganism to overcome the host defense mechanism

Tanada and Kaya (1993)OR

The severity of disease

Barr (1978)

Definition of Virulence

virulence

• Virulence is the measurement of the ability to cause a disease in host

• It describes the quantitative negative effect on host.

Pathogenicity

• Pathogenicity is the ability to cause a disease in host organisms

• The pathogenicity is a qualitative measurement

Differentiation between Virulence and Pathogenisity

Poly saccharides.

Plant cell wall degrading enzymes.

Type three secretion system.

Growth regulators.

Virulent proteins

Many plant pathogens produce large amount of exopolysaccharides.

EPS’s are carbohydrate polymers that are secreted by bacteria and form either a closely attached capsule layer surrounding the bacterial cell.

FunctionsFacilitate absorption of water, minerals and nutrients.Providing protection against abiotic stressesPromoting colonizationContributing to the production of disease.

Poly saccharides

Plant cell walls are composed of several complex carbohydrate polymers, the most abundant of which are cellulose, hemicellulose, and pectin.

Many plant pathogens include a battery of cell wall degrading enzymes in their repertoire of virulence factors.

Pectinases Cellulases Proteases

Plant cell wall degrading enzymes

Plant hormones, which are also often referred to as ‘‘plant growth regulators,’’ are endogenous signaling molecules important for many aspects of plant growth and development.

Growth regulators

Auxin Ethylene CytokininsAbscisic acidGibbberellins

T3SS are complex bacterial structures.

Found in Gram –ive bacteria.

Pilus like structure called Hrp pili.

Type three - secretion system

The hypersensitive response (HR) is a mechanism, used by plants, to prevent the spread of infection by microbial pathogens. 

The HR is characterized by the rapid death of cells in the local region surrounding an infection.

The HR serves to restrict the growth and spread of pathogens to other parts of the plant.

Hypersensitive response

A plant disease is any physiological or structural abnormality that is caused by a living organism.

It is a physiological process that affects some or all plant functions.

Disease is a process or a change that occurs over time. It does not occur instantly like injury.

Plant disease

Visible effects of disease on plants are called symptoms.

Any detectable changes in color, shape, and/or functions of the plant in response to a pathogen is symptom.

Symptoms

Bacterial spot of tomato

Mosaic on cucumber.

Anthracnose of mangoGalls produced by root knot nematode