BASIC OF PHYTOPATHOLOGY

2. LECTURE

CAUSES AND AGENTS OF

PLANT DISEASES AND DISORDERS

© 2012 A. Lebeda, B. Mieslerová, M. Sedlářová

CAUSES AND AGENTS OF

PLANT DISEASES AND DISORDERS

I. Abionosis -Non-infectious causes or physiological disorders

• Extreme temperatures

• Extreme soil wetness

• Excess or lack of light

• Oxygen deficiency

• Air pollution, exposure to emissions

• Nutrient deficiency (macroelements (K,Ca), microelements (B))

• Inappropriate pH

• Inappropriate agrotechnic management

• The toxicity of pesticides

• Toxicity of minerals

CAUSES AND AGENTS OF

PLANT DISEASES AND DISORDERS

II. Infections (biotic) disease (and damage)

• Viruses and viroids

• Prokaryots (Bacteria and Phytoplasmas)

• Fungi

• Parasitic higher plants and green algae

• Protozoa

• Nematodes, mites, insects

EXAMPLES OF ABIOTIC DISORDERS

EXAMPLES OF ABIOTIC DISORDERS

Frost damage of cherries (Prunus)

Drought in Spruce (Picea)

Ozone damage on Nicotiana tabacum

INFECTIOUS AGENTS OF DISEASES

Bionosis – infectious diseases

A. NON-CELLULAR ORGANISMS

A.1. Viroids

A.2. Viruses

B. PROKARYOTIC ORGANISMS

B.1. Bacteria

B.2. Phytoplasmas

C. EUKARYOTIC ORGANISMS

C.1. Fungi

C.2. Algae

C.3. Higher plants

C.4. Protozoa

C.5. Nematodes, mites, insects

MORPHOLOGY AND WAYS OF MULTIPLICATION OF SOME OF THE GROUPS

OF PLANT PATHOGENS

SCHEMATIC DIAGRAM OF

THE VARIOUS PLANT

PATHOGENS IN HOST

CELL

A.NON CELLULAR ORGANISMS

A.1. Viroids

Uncoated, small, circular, single-stranded RNA, which replicated

autonomously when inoculated into a host plant.

They differ from viruses or bacteriophages by absence of a protein

capsid and a small genom.

The smallest known agents of infectious plant diseases.

Discovered to r. 1971, until most of the diseases caused by viroids

were considered to be viral diseases.

It is not known how viroids actually replicate probably all

components necessary for their replication provides host.

Pathogenesis modifies metabolic regulatory networks, the

transcription of a number of genes, transcription factors and their

ability to activate promoters

A.NON CELLULAR ORGANISMS

A.1. Viroids

Most of viroids is localized in the nucleus of the host cell, usually

they are transmitted by sap (míza) also by pollen or vegetatively.

They are resistant to high temperatures.

Most of viroids causes in the infected plants no symptoms.

General symptom of infected plants are dwarf growth, epinastic

deformation and creased leaves.

To date, it was found that around 40 different plant diseases are

caused by viroids. Viroids act only disease in plants. They were not

found in animals and humans.

Taxonomy of viroids

Avsunviroid (ASBVd)-replication occurs in chloroplasts

Pospiviroid (PSTVd)- replication occurs in nucleus

Unassigned viroides

SYMPTOMS CAUSED BY VIROIDS

Potato spindle tuber disease

Chrysanthemum

stunt disease

Examples of diseases caused by

viroids

POTATO SPINDLE TUBER - Potato

spindle tuber viroid (PSTVd)– It causes

big losses, attacks all varieties and is

spreading rapidly

CHRYSANTHEMUM

STUNT (Chrysanthemum stunt

viroid – CSVd)

CACANG-

CADANG of

COCONUT PALM (Coconut cadang-

cadang CCCVd) –

On Phillipines

devastates coconut

palms

CITRUS

EXOCORTIS

(Citrus

exocortis

viroid)

A. NON CELLULAR ORGANISMS B. A. 2. Viruses

Obligate parasites reproducing only in host cells (replication is

dependent on the host cell). They usually have a very narrow host

range.

They attack all species of living organisms, distinguish plant

viruses, animal viruses and bacteriophages (viruses on bacteria).

Recently it is described about 2000 species of viruses, half of them

infecting the plant.

Diseases caused secondly disturbance of metabolism in the cells

and the use of energy in cells.

STRUCTURE OF VIRAL PARTICLES

• Virion - virus particles,

which is composed of

protein and one type of

nucleic acid (ss RNA, ds

RNA, ss DNA, ds DNA)

• Protein component -

capsid not only protects

the nucleic acid, but

generally increases the

infectivity of the virus

ELECTRON

MICROPHOTOGRAPHS OF

DIFFERENT MORPHOLOGICAL

TYPES OF VIRUSES

A. NON CELLULAR ORGANISMS B. A. 2. Viruses

TRANSFER - viruses get into cells mostly through injuries or

transmission of sucking insects, nematodes, by fungal vectors

(Polymyxa, Spongospora, Olpidium), seeds, pollen, vegetative

propagation. In the plant virus spreads by plasmadesm and then

by the vascular bundles.

SATELIT VIRUSES They represent the highest level of parasitism.

These are virus particles, which can not occur separately, but only

with a different virus particles - in the tobacco mosaic virus

(Tobacco necrosis satelite virus). Their replication is dependent on

the synthesis of viral RNA.

PROTECTION AGAINST VIRUSES - quarantine: control of vectors -

insects, using clear seeds, virus inactivation by heat. It is not yet

known chemical control.

PLANT VIRUS TRANSMISSION

PLANT VIRUS TRANSMISSION

II.

INSECT VECTORS OF PLANT VIRUSES

TRANSMISSION OF PLANT VIRUSES BY NEMATODES, MITES AND

FUNGI

SYMPTOMS OF VIRUSES ON

PLANTS

VIRAL PLANT – growth retardation,

dwarfism, shortened internodes, wilting

Histological

symptoms –

hyperplasy,

hypoplasy,

necrosis

Cytological

changes –

formation of

incluses

LEAVES – chlorotic or

necrotic lesions, mosaic, vein

yellowing, stripes,

deformaiton

FLOWERS - the colorfulness of

the flowers, streaking

SYMPTOMS OF VIRUSES ON PLANTS

SYMPTOMS OF VIRUSES ON PLANTS

CURRENT PLANT VIRUSES TAXONOMY

I: Single-stranded (+)sense DNA (+ ssDNA) single stranded DNA

II: Double-stranded DNA with RNA intermediate (ds DNA (RT) (double

stranded DNA, replicates using reverse transcriptase)

III: Single-stranded (+)sense RNA (+ ssRNA) single stranded RNA

(replicate using polymerase; RNA with function m-RNA)

IV: Single-stranded (-)sense RNA (-ssRNA) single RNA complementary

to m-RNA

V: Single-stranded (+)sense RNA with DNA intermediate in life-cycle

(ssRNA (RT)) single stranded RNA (replicates using reverse transcriptase)

VI: Double-stranded RNA (dsRNA) double stranded RNA

REPRESENTATIVE EXAMPLES OF INDIVIDUAL GROUPS OF VIRUSES

I. ssDNA – single stranded DNA -

Geminiviridae – Maize streak virus (MSV)

On maize (Zea mays)

II. (ds DNA (RT) double stranded

DNA, replicates using reverse

transcriptase Cauliflower mosaic virus (CaMV) –

on cauliflower (Brassica oleracea

var. botrytis)

III. (+) sense ssRNA viruses (single stranded RNA (replicate using

polymerase; RNA with function m-RNA)

Bromoviridae, Caliciviridae, Comoviridae, Coronaviridae (Pea enation

mosaic virus), Potyviridae (Potato virus Y), Flaviviridae, Leviviridae

(Tobacco necrosis virus, Barley yellow dwarf virus), Sequiviridae,

Tetraviridae (Tobacco mosaic virus), Tombusviridae

Pea enation

mosaic virus

(PEMV) – on pea

(Pisum sativum)

Barley yellow dwarf

luteovirus (BYDV)

on barley (Hordeum

vulgare)

Tobacco mosaic virus (TMV)

on tobacco (Nicotiana

tabacum)

IV. (-) sense ssRNA viruses – single RNA complementary to m-RNA

Rhabdoviridae (Lettuce necrotic yellows virus), Bunyaviridae,

Orthomyxoviridae.

V. ssRNA (RT) single stranded RNA (replicates using reverse transcriptase)

Pseudoviridae

VI. ds-RNA – double stranded RNA -

Reoviridae

Rice ragged stunt virus (RRSV)

on rice (Oryza sativa)

Lettuce necrotic

yellows virus (LNYV)

- on lettuce (Lactuca

sativa)

B. PROKARYOTIC ORGANISMS

ONLY REPRESENTATIVES OF GROUP BACTERIA CAUSE PLANT DISEASES

B. TAXONOMY of BACTERIA

BACTERIA AS PLANT PATHOGENS

GRACILICUTES (GRAM-NEGATIVE BACTERIA)

CLASS: PROTEOBACTERIA

(families Enterobacteriaceae (Erwinia), Pseudomonadaceae

(Pseudomonas, Xanthomonas), Rhizobiaceae (Agrobacterium)

FIRMICUTES (GRAM-POSITIVE BACTERIA)

CLASS ACTINOBACTERIA

Streptomyces, Clavibacter

CLASS FIRMICUTES

(Bacillus, Clostridium)

MOLLICUTES (Spiroplasma, Phytoplasma)

BACTERIAL TAXONOMY

• Bacterial /Archaeal species are defined on the basis of phenotypic

and genotypic differences.

• A bacterial strain is a population of organisms that descends from

a single organisms or pure culture

• A bacterial species is a collection of strains that share main stable

characteristics and differ significantly from other groups of strains

BIOVARS – differ biochemically or physiologically

MORPHOVARS – differ morphologically

SEROVARS – differ in antigenic properties

B.1. BACTERIA

Prokaryotic organisms, their DNA is not coated by nuclear membrane.

Do not contain membrane organelles (mitochondria, nucleus, plastids

..)

They have cell walls (one exception representatives of - Mollicutes).

They have tremendous ability of propagation (usually division, and

budding)

They occur mainly in warm and moist areas

Expansion of bacteria - water, insects, animals, humans

MORPHOLOGY OF BACTERIA - bacteria can be

rod-shaped, oval, spiral, fibrous, with flagella or

without flagella, they can produce spores or not.

Protein capsid. Nucleoid - a circle of DNA;

plasmids.

DETERMINATION OF BACTERIA : shape, number

and location of flagella, Gram stain, infestation

symptoms (wilting, spotting), cultivation - shape,

coloration of colonies, biochemical tests,

serology, molecular identification methods –

RFLP, PCR.

Monotricha

Polytricha

Monopolar Peritrich

Number of flagella: monotrichous (1),

polytrichous (more than 1)

The arrangement of flagella:

monopolar, bipolar, lofotrich, peritrich,

amfitrichal, atricha

MORPHOLOGY OF BACTERIA

Amfitrich

(bipolar

lofotricha)

Lofotrich

Rod-shaped (A), oval

(B,C,D), spiral (E), fibrous

(G) G

MEANS OF DISSEMINATION OF BACTERIA (AND FUNGI)

Anthracnosis, necrosis

Xanthomonas campestris

Pseudomonas syringae pv.

lachrymans

Bacterial wilting - break down

the walls of the xylem

Erwinia tracheiphilla

SYMPTOMS OF BACTERIA

INFECTION ON PLANTS Discoloration

Clavibacter michiganense

wallnut

Bacterial soft rot

Erwinia carotovora subsp.

Carotovora /Pectobacterium/

SYMPTOMS OF BACTERIA INFECTION ON PLANTS II.

Bacterial canker

Pseudomonas syringae

pv. syringae

Formation of tumors

Agrobacterium tumefaciens

Bacterial common scab

Streptomyces scabies

SYMPTOMS OF BACTERIA INFECTION ON PLANTS III.

Soil bacteria on the roots of

legume plants

Capable of fixing of

atmospheric nitrogen

Rhizobium sp.

SIMPLE SCHEME FOR THE DIFFERENTIATION OF GROUPS OF

PHYTOPATHOGENIC BACTERIA

THE MOST IMPROTANT GENERA OF BACTERIAL PLANT PATHOGENS

GRAM NEGATIVE (PROTEOBACTERIA)

Agrobacterium – is closely related to the genus Rhizobium, it causes

tumors by genetically modifying host cells to tumor cells

Erwinia/Pectobacterium – mobile, pectolytic enzymes, infects only

plants

Pseudomonas – causing spotting and cancer, have a wide host

range and also live on the surface of epiphytic plants

Ralstonia – previously referred to the genus Pseudomonas – but it

differs in that it does not produce fluorescent enzymes

Xanthomonas – have a high host specificity and cause wilting and

leaf blotch

Xylella - aerobic, unicellular and producing long chains under

certain conditions, requires special media, because normally

inhabits the xylem.

GRAM POSITIVE (FIRMICUTES)

Clavibacter (Corynebacterium) - mostly immobile

Streptomyces - form mycelium (chains cells), produce antimicrobial

substances against fungi, bacteria, algae, viruses, protozoa and

tumor tissues

Agrobacterium

GRAM NEGATIVE BACTERIA (PROTEOBACTERIA)

Erwinia

/Pectobacterium/

carotovora Erwinia amylovora

Pseudomonas

Pseudomonas

syringae var.

syringae

GRAM NEGATIVE BACTERIA (PROTEOBACTERIA)

Ralstonia

solanacearum

Xanthomonas

Xanthomonas campestris

pv. campestris

GRAM NEGATIVE BACTERIA (PROTEOBACTERIA)

Xylella fastidiosa

Clavibacter michiganensis

GRAM – POSITIVE BACTERIA (FIRMICUTES)

Streptomyces scabies

THE MOST IMPORTANT GENERA OF PLANT PATHOGENIC BACTERIA

B. PROKARYOTIC ORGANISMS

B.2. MOLLICUTES

MOLLICUTES –

They are referred to the group Bacteria

Prokaryotic organisms without a cell wall, only having plasma

membrane

About 200 disease is caused by these organisms

There are two types:

Spiroplasms - has a distinctive helical morphology

Phytoplasms - oblong, or round, but not spiral

Phytoplasms not to be grown on artificial media

In contrast, some Spiroplasma may be grown on artificial media and

transferred to healthy plants

Previously, these organisms considered to be identical with

mykoplasms (also Mollicutes class, rather that attack animals and

humans), however, genetic studies show that they are distant.

PHYTOPLASMS – previously: Mycoplasma-like organisms -

spherical or oblong, it is not yet possible to cultivate the media

Present in the vascular tissue, they are transmitted by insects,

sensitive to antibiotics -tetracyklins, and at a temperature higher than

37 ° C.

EXAMPLES OF DISEASES CAUSED BY PHYTOPLASMAS

Aster yellows

Apple proliferation

on apple (Malus

domestica)

European stone fruit

yellows

Pear decline on on pear

(Pyrus communis)

Grapevine yellows on

grapevine (Vitis vinifera) Peach X disease

On peach (Prunus persica)

SPIROPLASMAS - has a distinctive helical morphology

Transfer by insects

They may be isolated in pure form from insect vectors and

cultured on artificial medium

EXAMPLES OF DISEASES CAUSED BY SPIROPLASMAS

Citrus stubborn disease

Caused by: Spiroplasma

citri

Corn stunt disease

Caused by:

Spiroplasma kunkelli

SYMPTOMS CAUSED BY MOLLICUTES

EUKARYOTS

Oomycota

Fungi

Insects, mites,

nematodes

Parasitic plants

and Algae

Rhizaria

Plasmodiophorida

SAR

• SAR or Harosa (informally the SAR supergroup) is a clade that

includes STRAMENOPILES (heterokonts), ALVEOLATES, and

RHIZARIA

• The first letter of each group provides the "SAR" in the name

• Members of the SAR supergroup were once included under the

separate supergroups CHROMALVEOLATA and RHIZARIA, until

phylogenetic studies confirmed that stramenopiles and alveolates

diverged together with Rhizaria.

PLASMODIOPHOROMYCOTA

Plasmodiophora brassicae,

cause CLUB ROT

Spongospora subterranea

Cause POWDERY SCAB Beet necrotic yellow vein virus – transfer

by fungus Polymyxa betae

RHIZARIA, group PHYTOMYXEA

• They typically develop within plant

cells, causing the infected tissue to

grow into a gall or scab.

• Important diseases caused by

phytomyxeans include CLUB ROOT in

cabbage and its relatives, and

POWDERY SCAB in potatoes. These

are caused by species of

Plasmodiophora and Spongospora,

respectively.

LIFE CYCLE - PLASMODIOPHORA BRASSICAE

STRAMENOPILA

• The heterokonts or stramenopiles (formally, Heterokonta or

Stramenopiles) are a major line of eukaryotes currently containing

more than 25,000 known species.

• Most are algae, ranging from the giant multicellular kelp to the

unicellular diatoms, which are a primary component of plankton.

• Other notable members of the Stramenopiles include the

(generally) parasitic oomycetes, including Phytophthora of Irish

potato famine infamy and Pythium which causes seed rot and

damping off.

• Unicellular or filamentous

organisms, cell wall composed

mostly of cellulose

• Flagella (if present) having at least

one flagellum with rigid

mastigonemata.

DIVISION : OOMYCOTA • They are filamentous, microscopic,

absorptive organisms that reproduce

both sexually (oogonium and

antheridium – oospore) and asexually

(zoospores in sporangium).

• Oomycetes occupy both saprophytic

and pathogenic lifestyles

SYMPTOMS OF OOMYCOTA INFECTION

OOMYCOTA

Phytophthora infestans Pythium debaryanum Bremia lactucae

Pseudoperonospora

cubensis

Plasmopara viticola

LIFE CYCLE - PLASMOPARA VITICOLA