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BASIC OF PHYTOPATHOLOGY

2. LECTURE

CAUSES AND AGENTS OF

PLANT DISEASES AND DISORDERS, part II.

© 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 deficiecy

• Air pollution, exposure to emissions

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

• Inappropriate pH

• Inappropriate agrotechnic

• The toxicity of pesticides

• Toxicity of minerals

CAUSES AND AGENTS OF

PLANT DISEASES AND DISORDERS

II. Infectious (biotic) disease (and damage)

• Viruses and viroids

• Prokaryots (bacteria and Phytoplasmas)

• SAR (Chromista, Rhizaria)

• Fungi

• Parasitic higher plants and green algae

• Protozoa

• Nematodes, mites, insects

C. EUKARYOTIC ORGANISMS

C.2. FUNGI

• Fungi are eukaryotic organisms that includes unicellular

microorganisms such as yeasts and molds, as well as multicellular

fungi that produce familiar fruiting forms such as mushrooms.

• Fungi are heterotrophs; they acquire their food by absorbing dissolved

molecules, typically by secreting digestive enzymes into their

environment.

• Fungi do not photosynthesise.

• They have cell wall composed from chitin.

• Fungi are the principal decomposers in ecological systems.

• Fungi include saprotrophs (living on dead material), symbionts of

plants, animals, or other fungi and also parasites.

A PHYLOGENETIC TREE OF FIVE GROUPS OF FUNGI

TAXONOMY OF FUNGI

DIVISION: CHYTRIDIOMYCOTA

• Division of zoosporic organisms, informally known as chytrids.

• Chytrids are one of the early diverging fungal lineages, with chitin

cell walls, a posterior smooth flagellum, absorptive nutrition.

• Chytrids are saprobic, degrading refractory materials such as

chitin and keratin, and sometimes act as parasites.

Synchytrium endobioticum

causing potato ward disease

Rhizophydium on algae

Spirogyra

DIVISION: MICROSPORIDIOMYCOTA

• The Microsporidia constitute a group of spore-forming unicellular

parasites. They were once considered protozoans or protists, but

are now known to be fungi, or a sister group to fungi.

• Microsporidia are restricted to animal hosts, most infect insects,

but they are also responsible for common diseases of crustaceans

and fish.

Sporoblast of

Fibrillanosema crangonycis

Nosema apis infecting bees

DIVISION: ZYGOMYCOTA

• Zygomycete hyphae may be coenocytic, forming septa only

where gametangia are produced. Zygosporangia are

characteristically formed by the members of this clade.

• They are mostly terrestrial in habitat, living in soil or on

decaying plant or animal material.

• Some are parasites of plants, insects, and small animals, while

others form symbiotic relationships with plants

Rhizopus nigricans

Rhizopus arrhizus on

strawberries

DIVISION: GLOMEROMYCOTA

• Members of the Glomeromycota form arbuscular mycorrhizas (AMs)

with the roots or thalli (e.g. in bryophytes) of land plants.

• The arbuscular mycorrhizal species are terrestrial and widely

distributed in soils worldwide where they form symbioses with the

roots of the majority of plant species (>80%). They can also be

found in wetlands, including salt-marshes, and associated with

epiphytic plants.

Gigaspora and Glomus

DIVISION: ASCOMYCOTA

• Its members are commonly known as the sac fungi or ascomycetes.

• They are the largest phylum of Fungi.

• Defining feature of this fungal group is the "ascus„ microscopic sexual

structure in which nonmotile spores, called ascospores, are formed.

• Some species of the Ascomycota are asexual, reproducing via conidiophores.

• They are important for humans as sources for medicinally important

compounds, such as antibiotics and for making bread, alcoholic beverages,

and cheese, but also as pathogens of humans and plants and symbions

(lichens)

Tuber

Black Truffle

Saccharomyces cerevisiae

yeast Powdery mildew

conidiophore

DIVISION: BASIDIOMYCOTA

• Basidiomycota are filamentous fungi composed of hyphae (except

for yeasts), and reproduce sexually via the formation of specialized

club-shaped end cells called basidia that normally bear external

basidiospores.

• The group include best known mushrooms as boletes, chantherelles,

polypores as same as plant parasites like smuts, rusts and human

pathogenic yeast Cryptococcus.

Boletus edulis King bolete Rust Cronartium ribicola on Ribes

MORPHOLOGY OF FUNGI

One-celled fungi

Holokarpic - whole

thallus developed into a

fruiting body or

sporangium Eukarpic - having only part of

the thallus transformed into a

fruiting body or sporangium

Hyphal fungi

Chytridiomycota

Mycelium septate (Ascomycota,

Basidiomycota)

Mycelium nonseptate (Chytridiomycota,

Glomeromycota and Zygomycota)

MORPHOLOGY OF FUNGI II.

Hyphae are clusters of cells in a fungus that grow in a

branch-like design

Mycelia are large groups of hyphae.

Large groups of mycelium make up the body of a fungus

Fungal tissue - PLECTENCHYM

Prozenchym Pseudoparenchym

MORPHOLOGY OF FUNGI III.

ASEXUAL REPRODUCTION

Sporangia and zoospores

Sporangia and sporangiospores

Conidiophores and

conidia

Chytridiomycota

Zygomycota

Ascomycota

Basidiomycota

MORPHOLOGY OF FUNGI IV.

Zygospora

Ascospores and ascocarps

Basidiospores and basidiocarps

Chytridiomycota

Ascomycota

Basidiomycota

Morchella conica

SEXUAL REPRODUCTION

Zygomycota

Zygote

TYPES OF SPORES IN PLANT PATHOGENIC FUNGI

SYMPTOMS OF PLANT PATHOGENIC FUNGI I.

Leaf spots, anthracnosis

Cercospora

beticola

Colletotrichum

lindemuthianum Sigatoga - Mycosphaerella

fijiensis

Cankers

Nectria galligena

Venturia inaequalis

SYMPTOMS OF PLANT PATHOGENIC FUNGI II.

Taphrina betulina Taphrina deformans

Witches' broom Leaf deformation

Wilting

Fusarium

oxysporum

SYMPTOMS OF PLANT PATHOGENIC FUNGI III.

Pythium sp.

Powdery mildew

Blumeria graminis Rust Cronartium ribicola

Root rot

Sporulating mycelium covering leaves

Wood decaying

SYMPTOMS OF PLANT PATHOGENIC FUNGI IV.

Brown rot - fungi break down

hemicellulose and cellulose; as a

result of this type of decay, the

wood shrinks, shows a brown

discoloration, and cracks into

roughly cubical pieces

White rot - break down lignin and

cellulose and commonly cause

rotted wood to feel moist, soft,

spongy, or stringy and appear

white or yellow.

CHYTRIDIOMYCOTA

Synchytrium endobioticum

causes potato wart disease

Olpidium brassicae -

causing seedling death

and transferring tobacco

necrosis virus

ZYGOMYCOTA

Rhizopus

nigricans on

peaches

Choanephora

causing

squash rot

ASCOMYCOTA

ASCOMYCOTA

Taphrina

deformans Taphrina betulina Taphrina pruni

Canker

Nectria galligena

Powdery mildew

Blumeria graminis Sphaerotheca fusca

(Podosphaera xantii) Podosphaera

leucotricha

ASCOMYCOTA

LIFE CYCLE OF SPHAEROTHECA PANNOSA

Claviceps purpurea Venturia inaequalis

Monilia (Monilinia) fructigena

Botrytionia fuckeliana (teleom.)–

Botrytis cinerea (anam.)

ASCOMYCOTA

LIFE CYCLE OF CLAVICEPS PURPUREA

Anthracnosis

Septoria apii Cercospora beticola

Colletotrichum

lindemuthianum

Mycosphaerella fragariae,

teleom.: Ramularia tulasnei

FOLIAR DISEASES CAUSED BY MITOSPORIC FUNGI (prev. DEUTEROMYCOTA)

DISEASES CAUSED BY MITOSPORIC FUNGI (prev. DEUTEROMYCOTA)

Alternaria

Cladosporium

Wilting

Verticillium sp.

Fusarium oxysporum

VASCULAR DISEASES CAUSED BY MITOSPORIC FUNGI (pr. DEUTEROMYCOTA)

BASIDIOMYCOTA

BASIDIOMYCOTA

Rusts

BASIDIOMYCOTA

Rusts

Cronartium ribicola Gymnosporangium

sabinae Puccinia graminis

Transchelia pruni-spinosae Phragmidium mucronatum

LIFE CYCLE OF PUCCINIA GRAMINIS

BASIDIOMYCOTA

Smuts

Ustilago maydis

Tilletia caries

Urocystis cepulae

LIFE CYCLE OF USTILAGO TRITICI

BASIDIOMYCOTA

Wood decaying fungi

Heterobasidion annosum

Armillaria

ostoyae BASIDIOMYCOTA

Pleurotus ostreatus Ganoderma applanatum

C. EUKARYOTIC ORGANISMS

4. ALGAE

Diverse group of PHOTOSYNTHETIC ORGANISMS which are

polyphyletic.

Included organisms range from unicellular genera, such as Chlorella

and the diatoms, to multicellular forms, such as the giant kelp

Parasites of plants cultivated in tropical and subtropical areas

The most important genus Cephaleuros (CHLOROPHYTA)

Cephaleuros virescens – can invade tea and other

tropical crops. Penetrates the host tissues by

unicellular rhizoids.

C. EUKARYOTIC ORGANISMS

C.3. PARASITIC HIGHER PLANTS

It is known about 3000 parasitic angiosperms

All parasitic plants have modified roots, named haustoria, which penetrate

the host plants, connecting them to the conductive system – either the xylem,

the phloem, or both.

Hemiparasites - plant that is parasitic under natural conditions and is also

photosynthetic to some degree. Hemiparasites may just obtain water and

mineral nutrients from the host plant (xylem)

Holoparasites - a parasitic plant that derives all of its fixed carbon from the

host plant. Commonly lacking chlorophyll, holoparasites are often colors

other than green (xylem and phloem)

Root parasite – a parasite that attaches to the host root (Orobanchaceae,

Scrophulariaceae)

Stem parasite – a parasite that attaches to the host stem (Cuscutaceae,

Lauraceae, Viscaceae)

C. EUKARYOTIC ORGANISMS

C.3. PARASITIC HIGHER PLANTS

Cuscuta sp. –

Dooder – holo/hemi

parasite of stems

Orobanche sp. – Broom-

rape - obligate root

holoparasite

Viscum album –

Mistletoe

Obligate stem

hemiparasite

Loranthus europaeus – stem

hemiparasite

DISEASE CYCLE OF DODDER (CUSCUTA)

Lathraea squamaria – root

holoparasite

Arceuthobium – dwarf mistletoe

- numerous dwarf mistletoe

species are considered to be

serious forest-borne disease

agents (mainly Pinaceae).

Severe dwarf mistletoe infection

can result in a reduction in tree

growth, premature tree

mortality, reduced seed and

cone development, reduced

wood quality, and increase the

susceptibility of the host tree to

pathogen and/or insect attack.

DISEASE CYCLE OF DWARF MISTLETOE (ARCEUTHOBIUM)

C. EUKARYOTIC ORGANISMS

C.4. FLAGELATE PROTOZOA

Protozoa that attack plants are classified into the tribe Euglenozoa,

order Kinetoplastidae and family Trypanosomatidae

They are flagellates, but because they do not meet some of Koch's

postulates (isolation and keeping in pure culture and re-inoculation on

healthy plants) are not yet fully accepted as plant pathogens

Phytomonas - the most common genus of protozoa infecting plants

Occurrence - South America

They are transmitted the most often by insect

Distribution by localization in tissues:

1. Lactifer- restricted Trypanosomatids - pathogenicity is debatable

2. Phloem restricted Trypanosomatids - (coffee, palm). Pathogenicity

is conclusive.

Examples: Hartrot of coconut palm – in mature sieve elements

Phloem necrosis of Coffee (roots die and then the whole plant)

Trypanosomatids of

genera Phytomonas

Hartrot of coconut palm

C. EUKARYOTIC ORGANISMS

C.5. NEMATODES, MITES, INSECTS

Animal pests in plant pathology - mostly just VECTORS of

zoonotic infectious diseases, injuries and causes FEEDING

DAMAGE.

Some nematodes, mites and insects damage plants in a similar

manner as true pathogens – they change physiological processes,

cause necrosis, hyperplasia, hypoplasia.

They produce different chemicals - PHYTOALLAKTINS

(enzymes, growth substances, toxic substances, able to change

the physiological processes of plants) - contained in secretions,

excretions of pests

PHYTOTOXICOSIS - diseases caused by Phytoallaktins

PLANT PATHOGENIC NEMATODES. 300 mm - 4 mm long. Part of his life living

in the soil, often attack the plants. However, there are two kinds of nematodes

that survive only in plants. May be ectoparasites, endoparasites.

MORPHOLOGY AND MAIN

CHARACTERISTICS OF

TYPICAL MALE AND

FEMALE PLANT

NEMATODES

SYMPTOMS OF INFECTION BY PLANT PARASITIC NEMATODES:

On roots: lesions, cysts on roots overgrowth surrounding the

roots

On the aboveground parts - reduced growth, yellowing, wilting,

poor quality of fruits.

Some nematodes attack also aboveground plant, where it causes

necrotic lesions, decay, abnormal development of flower parts.

Cysts

swollen

roots Yellowing of

aboveground

parts

DISEASE CYCLE OF ROOT KNOT (MELOIDOGYNE)

EXAMPLES OF PLANT PARASITIC NEMATODES

CYST NEMATODES :

Heterodera, Globodera

The presence of cysts on the roots, and

consequently production of excessively

branched root system.

Meloidogyne spp.

It infect about 2,000 species of plants,

root causes devitalization peaks, the

roots are swelling

NEMATODES Pratylenchus

They infect the roots, and thus inside

causing lesions and reduced growth.

http://www.cals.ncsu.edu/course/ent425/text18/plantvectors.html

INSECT VECTORS OF DISEASES

BEETLES

BEES

ANTS

FLIES

WHITEFLIES

APHID

MEALYBUGS

TRUE BUGS