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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