SAR-Systemic Acquired Resistance

1. PAT202 principles of plant
disease management(1+1)
SAR-Systemic Acquired Resistance
V.Vanaja Vasudevan
2017028091
Rvs Agricultural College
Thanjavur
Course Teacher:
K. Ramalingam
Assistant professor
(pathology)

2. DEFINITION
Systemic Acquired Resistance (SAR) is plant
defense a mechanism of induced defense that
confers long-lasting protection against a broad
spectrum of microorganisms & pest.

3.  Presently disease control is largely based on the use of
hazardous chemicals viz., fungicides, bactericides and
insecticides for either direct or indirect disease
management.
 The hazardous natures of the products on the
environment, human and animal health strongly
necessitates to search for new safer means of disease
control.

4.  SAR have high potential to diminish the use of toxic
chemicals in the agriculture and has emerged as an
alternative, non-conventional, non-biocidal and eco-
friendly approach for plant protection and hence for
sustainable agriculture.
 SAR requires the signal molecule salicylic acid (SA)
and is associated with accumulation of
pathogenesis-related proteins, which are thought to
contribute to resistance

5.  A distinct signal transduction pathway that plays an
important role in the ability of plants to defend
themselves against pathogens…..
 Significant phenomenon recognized by Chester in 1933.
 Concept of SAR proposed by Ronald Ross in 1961.

6.  Infection of plants with necrotizing pathogens
(causing HR) often results in enhanced resistance to
subsequent infections by a variety of bio-tropic
pathogens.
 Resistance triggered in the plant during its life time
is Acquired Resistance. Local (LAR) confined to
few cells or tissues Systemic (SAR) having been
moved through out the plant

7. PR PROTIENS IN SAR
 Pathogenesis related proteins (PRs) are assigned an
important role in plant defense against pathogenic
constraints and in general adaptation to stressful
environment.
 These proteins are accumulated 7-10 days after
infection and indicate the attainment of SAR.
 It is accumulated in the intercellular spaces (first line
of defence) and vacuole (second line of defence by

8. SAR Characteristics
 Necrotic lesions (pp) as inducing agent
 Involvement SA signaling
 Expression of PRprotein
 Broadspectrum
 SAR depend on plant & inducing factor

9. IMPORTANT OF SAR IN PLANT DISEASE
MANAGEMENT
 SAR can also be transmitted to the next generation progeny.
 Its provides a broad-range resistance against fungal, bacterial
and viral pathogens.
 Leads to pathogenesis-related (PR) gene expression.
 Its ability to immunize susceptible plants implies that genetic
potential for resistance is in all types of plants.

10.  The significant practical aspects of SAR is the
discovery of chemical inducers of plant defense.
 New generation fungicides act as a plant defense
system. (rather than killing pathogen.) ICGA-245704,
a benzothiadiazole (BTH) (Alfa-Aesar) &
Dichloroisonicotinic acid (DCINA) compound (plant-
activator) switches SAR in plant.

11. SAR INDUCING CHEMICALS / PLANT
ACTIVORS/ PLANT DEFENCE ACTIVORS
Plant activors are the chemicals that activate the defence genes in plant
by providing signal via the signal transduction pathway mediated by
salicylic acid.
Important plant activors
Acibenzolar-s-methyl
2,6-dichloroisonicotinic acid
probenazole
salicyclic acid
riboflavin
methyl jasmonate

12. SIGNAL TRANSDUCTION FOR SAR
 The first step in the development of SAR is the recognition
of pathogen infection by the plant.
 Once the plant reacts to the pathogen , signals are
released that trigger resistence in adjacent as well as
distant tissues.
 Not all the plant pathogen interactions lead to SAR
induction.
 Compatable interaction can lead to SAR induction; the
pathogen need not induce a gene for gene resistence
reaction

13.  SA has been proposed as one signal leading to SAR
because its concentration rises dramatically after a
pathogenic infection.
 SA as a signal in SAR comes from experiment using
transgenic tobacco to express the enzyme salicylate
hydroxylase,encoded by the nahG gene from PseudomonaS
Putida.
 The enzyme catalyses the conversion of Sato catechol,
which is not an active SAR inducer.

14.  The NahG expressing plants do not accumulate SA
in response to pathogen infections and are unable
to induce an SAR response to viral , bacterial or
fungal pathogen.
 These experiment implicate the direct
involvement of SA in SAR signalling , but they do
not address whether SA is the long distance ,
phloem mobile signal for SAR