General introduction

Phytopathology is the study field of plant diseases caused by pathogens and physiological factors. Plant pathology involves the study of pathogen identification, disease etiology, disease cycles, economic impact, epidemiology, plant disease resistance, effects on humans and animals and disease management.

Phytopathology

keywords

Plant Pathology Plant Pathology : The study of plant diseases: The study of plant diseases

Plant Disease Plant Disease : Any physiological or morphological change : Any physiological or morphological change in a plant that results in abnormal appearance in a plant that results in abnormal appearance

or development or development

Pathogen Pathogen : An organism that causes disease: An organism that causes disease

Host: The infected plantHost: The infected plant

Symptom Symptom : Abnormal appearance of a plant: Abnormal appearance of a plant

Components of a Plant Disease

- Conducive Environment- Conducive Environment

- Susceptible Host- Susceptible Host

- Virulent Pathogen- Virulent Pathogen

- Adequate Time- Adequate Time

TimeTimeDISEASEDISEASE

EnvironmentEnvironment

PathogenPathogen

Susc. Susc. HostHost

Components of a Plant Disease

Disease Classes

- Abiotic- Abiotic (not transmissible)(not transmissible)

- Biotic- Biotic (transmissible) (transmissible)

Causes of Abiotic Diseases

- Environmental (freezing, flooding, drought, light, wind, hail)

-Cultural (mechanical damage, planting problems)

-Chemical (fertilizers, herbicides, pets)

- Physiological Disorders (abnormal growth due to genetic and/or environmental interactions)

Causes of Biotic Diseases (Plant Pathogens)

VirusesViruses

Electron micrograph of purified tristeza virus particles negatively stained with uranyl formate. Bar represents 100 nm

BacteriaBacteria

Pseudomonas syringae bacterial cells on the surface of a bean leaf

(Phaseolus vulgaris)

FungiFungi

Pea Powdery MildewErysiphe pisi

Nematode (Meloidogyne sp. ) captured by a the mycelium of a

fungus at the moment of its penetration in the root

(Root-knot)

NematodesNematodes

Meloidogyne sp. Root-knot namatode penetrating a root

Parasitic PlantsParasitic Plants

Cuscuta campestris, parasitic on Glechoma hederacea. This is one of the most common species of dodder

worldwide.

Schematic representation of some Plant Pathogens

Plant Disease Groups(By Symptoms)

- Leaf Spots

- Leaf and Shoot Blights

- Mildews

- Rusts

- Cankers

- Root Rots- Root Rots

- Wilts- Wilts

- Galls- Galls

- Mosaics and Ringspots- Mosaics and Ringspots

Leaf Spots

Cause: Fungi, bacteria, insects, mites, or abiotic factors

Symptoms:

Circular or “somewhat circular” spots showing chlorosis (yellowing) or necrosis (brown and dead) areas on leaf

Photinia fungal leaf Spot Entomosporium mespili

Leaf and Shoot Blights

Cause: Fungi and bacteria

Symptoms:

Larger areas of leaves (not circular) and shoots showing localized discoloration and/or flagging

Dogwood Anthracnose(Fungal)

Wilts

Cause:Fungi (Verticillium, Fusarium) and Bacteria

Symptoms:Vascular PluggingWilted leaves and shoots

Verticillium WiltSmoke Bush

Dark colored xylem shows vascular plugging

Galls

Cause: Fungi, bacteria, insects, mites, nematodes, and abiotic factors

Symptoms:

Abnormal proliferation of plant tissue Specific to a certain plant organ (leaf, stem, crown or root)

Almond Leaf gallCurl Fungus

Rusts

Cause:Fungi

Symptoms:Fungal spore masses in yellow, orange, white, brown, and black on leaves and stems

Rust ribes host

Fungus requires two host to complete its life cycle. One part on Pinus and the other on Ribes.

Cankers

Cause:Cause:Fungi or bacterial infection resulting in dead, non-Fungi or bacterial infection resulting in dead, non-growing areas on stems and branchesgrowing areas on stems and branches

Symptoms:Symptoms:

Dark, sunken areas with distinct margins on stems Dark, sunken areas with distinct margins on stems sometimes have small red or purple fruiting bodiessometimes have small red or purple fruiting bodies

Same fungi also cause fruit rots (e.g. bulls-eye rot)Same fungi also cause fruit rots (e.g. bulls-eye rot)

Fungal apple Anthracnose

Notice sunken (dead) areas of trunk that have failed to grow and inrease in girth as the rest of the trunk (results in depressed canker)

Root Rots

Cause:Fungi (Armillaria, Phytophthora, Sclerotinia) and bacteria (Erwinia)

Symptoms:Shoot wilting, chlorosis/necrosis

Stem and root discolorationDead roots often with fungal hyphae growth under bark

Tomato (Stem and Fruit Rot)Tomato (Stem and Fruit Rot)

Mildews

Cause:Fungi

Types: - Powdery (common) “Dry” - Downy “Wet”

Symptoms:Chlorosis, yellowing or purple blotches on leaves. White hyphae and fruiting bodies (fuzzy looking) on plant (leaf) surface

Powdery MildewCucumber

Does not like free moisture. Likes high humidity (warm days and cool nights)

Abiotic Plant Disease(Not Transmissable)

Inability to uptake iron from pH neutral or basic soils. Not related to amount of iron (Fe) in soil.

Irregular watering appears as a brown spot at the base of the tomato fruit, this develops into a hard, sunken ring, caused by insufficient calcium flow.

Disease control

-Chemical treatments

-Biocontrol methods

-Development of resistant plant

- Cultural practices: crop rotation, good soil drainage, proper handling of the crop, adequate storage and efficient post-harvest operations

Biocontrol

Bacterial antagonist primary selection

Colletotrichium gloesporoides

Botrytis cinerea

Fusarium oxysporum

Fusarium culmorum

B31

B8

B29

B12

B42B31

B12

B29 B42

B8

B8

B29

B42

B12

B31

T 19°C T 30°CT 25°C

Direct confrontationDirect confrontationTemperature effect on the antagonistic bacterial activity

Perc

enta

ge o

f in

hibi

tion

T…

T…

T…

0

10

20

30

40

50

60

70

80

90

B8 B31 B29 B12 B42

Inh

ibit

ion

de

la

cro

iss

an

ce

myc

éli

en

ne

(%

)

Souches abtagonistes

Antagonisme bactérien contre P. tracheiphila

T 19 T25 T30

°c °c °c

Strains

Bacterial antagonisme

Inhibition de la croissance mycélienne par les protéines de la souche B8

A: mycelium growth inhibition ( 70.80% ) by bacterial protein of B8 ( proteins are at 0.356µg /well). B: mycelium development on PDA medium without bacterial extract proteins.

A B

Effet of the proteine treatment on the disease development

00.51

1.52

2.53

3.54

4.55

0 8 15 20 24 28 32 36

T1 T2 T3 T0

Indi

ce o

f th

e di

seas

e

Days

Development of resistant plant

A B

D C

A. in situ initiation of callogenesis from ovules explants by transversal cutted of younger fruits; B. white cals proliferation from ovular explants; C. development of the isolateds cals on MS+NAA; D. green organogenesis cal.

in situ induction and development of ovular cals

A B

A: adventive buds formation from ovular cals on MS+BAP; B: young shoot formation from ovular cals on MS+BAP medium.

Formation of structural organogene cal from ovulair explants

Artificial MS medium.

Dicotylydonary embryos cal obtained from styl explant.

A: Friable cal with embryogenic structures B: Initiation of the rhizogenic structures. D: developed root from friables cals

Organogenesis obtained from no zygotic parts of seeds

A B

C

Plant regeneration from friable cals induced from non zygotic parts of the seeds

A: shoot regeneration on MS+BAP+2,4-D medium; B: young plant regenerated from friable cals; C: Vitroplant de Citrus eurêka developed in vitro on MS medium.

BA

C

- Mal secco : Vasculare disease, Tracheomycosis

- Causal Agent: Phoma tracheiphila (Ciccarone, 1971)

- Hot: Citrus limon

- Geographic distribution:

• Mediterranean sea region

• Black sea costs

Highly contaminated Zones

Lower contaminated Zones

Geographic Distribution of the Mal secco disease

A

D

B

C E

A: Pycnidia of P. tracheiphila on lemon dying shoot; B: Mucilaginous pycnidia gel (the cyrrhus) containing pycnidiospores.

A: Mycelium; B: Pycnidium; C: Phialoconidia; D: Arthroconidia; E: Pycnidiospores

A

B

Total lemon diedback caused by the fungal infection

DisseminationDissemination

• Conidia transportation

- Anemophilous - by water

- Entomophily

• vegetable material exchanges (Homme)

- By birds

Phoma tracheiphila

DPR

DP

RPycnides

Red Pigment

PycnidesAbsence of red pigment

SterileRed Pigment

Types of Types of P. tracheiphilaP. tracheiphila

Morphological varaibility of P. tracheiphila isolates

Isolation of the parasite

Double stranded Eeectrophoretic profil of the Avirulent isolate on agarose gel ( 1 % )

9 kb10 kb

3 kb

1 2 3 4 5

Référence de l’isolat Date de l’isolement Origine géographique Plante hôte  Type

 V29

 2001

 Bizerte

 Eureka Chromogène

VK 1998 Nabeul lime douce ChromogèneV22 2001 Tunis Eureka ChromogèneV25 2001 Tunis Eureka ChromogèneV23 2001 Nabeul Eureka ChromogeneVH2 2001 Bizerte Eureka ChromogèneVX 2001 Tunis Eureka ChromogèneV4 2001 Tunis Eureka Chromogène

V14 2001 Nabeul Eureka ChromogèneV30 2001 Nabeul Eureka ChromogèneV12 2001 Nabeul Eureka ChromogèneV13 2001 Nabeul Eureka ChromogèneVD 2001 Tunis Eureka ChromogèneVY 2001 Tunis Eureka Chromogène

VH3 2001 Nabeul Eureka ChromogèneV21 2001 Nabeul Eureka ChromogèneV2 2001 Nabeul Eureka Chromogène

VPM 2000 Tunis Eureka ChromogèneV6 2001 Tunis Eureka ChromogèneV7 2001 Nabeul Eureka ChromogèneV8 2001 Tunis Eureka ChromogèneV5 2001 Tunis Eureka Chromogène

V24 2001 Tunis Eureka ChromogèneV26 2001 Tunis Eureka ChromogèneVT1 2001 Tunis Eureka ChromogèneV3 2001 Tunis Eureka Chromogène

VI26 - Italie - ChromogèneV28 2001 Tunis Eureka ChromogèneV66 - Italie - ChromogèneV10 2001 Tunis Eureka ChromogèneV11 2001 Tunis Eureka ChromogèneVI1 - Tunis - ChromogèneV48 - Tunis - ChromogèneV27 2001 Bizerte Eureka ChromogèneVR 2000 Tunis Eureka N. ChromogèneVPt 2000 Tunis Eureka N. Chromogène

         

P. Tracheiphila collection isolates

Phytosanitary evaluation

- Field infection

- Greenhouse artificial infection

- In vitro artificial infection disease system

Field infection

Empirical scale of evaluation

0 : No drying symptoms

1 : Limited drying to the annual shoots

2 : Drying reach the two years branches

3 : Drying exceeded to the main branches

4 : Trunk drying

5 : Total drying and death of the infected plant

Greenhouse artificial infection

Inoculations MethodsInoculations Methods

Foliar inoculation Stem inoculation Root inoculation

Foliar inoculation

0= No symptoms; 1= Chlorosis on the inoculation point; 2= Chlorosis around the inoculation point; 3= Chlorosis extended till the foliar borders; 4= general chlorosis; 5= foliar necrosis.

Stem and root Inoculation

0= No symptoms; 1= Chlorosis at principal vein of the upper leaves; 2= General chlorosis of the upper leaves; 3= Apical necrosis of the branches; 4= Necrosis extended to the trunk of the inoculated plant; 5= Total necrosis and death of the inoculated plant.

In planta toxin inoculation

In vitro artificial infection disease system

VR

Te

VPt

V11

V21

VH2 V13

Foliar phytotoxicity toxin Test

V13: Isolat de G1

VH2: Isolat de G2

V21: Isolat de G3

V11: Isolat de G4

VR: Isolat de G5

VPt: Isolat de G5

Te: non treated by the toxin

Development of new technic of artificial reproduction of the disease

Parameters:

1- Micropropagated stem necrosis (Fig. a)

0= No symptomes; 1= Necrosis under the 1/3 of the micropropagated stem; 2= Necrosis between 1/3 et 2/3 of the micropropagated stem; 3= Necrosis exceed 2/3 of the micropropagated stem; 4= Total necrosis of the micropropagated stem.

2- Inhibition of the regeneration (Fig. b)

0= No regeneration; 1= Initiation of regeneration; 2= Young shoot; 3= shoot with foliar formation.

20 1 3

ba

Classification of P. tracheiphila isolates