Zvyšování konkurenceschopnosti studentů oboru botanika a učitelství biologie

CZ.1.07/2.2.00/15.0316

© 2011 B. Mieslerová, A. Lebeda, (KB PřF UP v Olomouci)

PARASITIC SYMBIONTSFungi come into association with their host, but inPARASITIC SYMBIOSIS only fungus benefits and the host is harmed

FUNGAL PARASITES OF PLANTS, ALGAE AND OTHER FUNGI

FUNGAL PARASITES OF PLANTSPlants are attacked by insect, fungi, bacteria and viruses.However, about 60% of all plant diseases are caused by fungi.

CLASSIFICATION OF PARASITIC FUNGIOBLIGATORY PARASITES – strictly depend on parasitic life style (e.g. Erysiphales) FACULTATIVE PARASITES - organisms that can live either saprophitically or parasitically. Many of these are pathogens of crop plants, and must survive between growing seasons as members of the normal soil mycota (Fusarium oxysporum). Some of them are pertotrophs – living on dead tissue in live organism.

CLASSIFICATION OF PARASITIC FUNGI II. BIOTROPHIC PARASITES - parasite and host live together for longer periods of time. The parasite takes nutrients but does not kill it. Most biotrophic fungi are obligatory parasites.NECROTROPHIC PARASITES - necrotrophs kill host cells before they penetrate them by the secretion of extracellular cell wall degrading enzymes or toxins or both. Many necrotrophs show low specificity to host plants (Botrytis cinerea).The fungi are often only optionally parasitic, they can just as well proliferate in dead or withering plant material (facultative parasites).

GENERALIZED FUNGAL DISEASE CYCLE

FUNGAL INFECTION

INOCULATION - Zoospores of Pythium, Phytophthora show tropism towards root exudates (taxe of zoospores)

INITIAL CONTACT – attachment (extracellular matrix release), adhesion, appressorium development and growth on the plant surface.

Initial events of colonization – the fungus recognizes its host (elicitors-receptor)

APPRESSORIUM – structure specialized for firm attachment which is formed at the tip of hypha – enables the infection peg to exert mechanical pressure against the cell wall. The development of high internal pressure is essential for infection.

Germinating powdery mildew conidia with appressorium

PENETRATION By stomata (rusts)

By wounds (Venturia, Sclerotinia fructigena)

By younger parts of tissue (root hairs)

Direct penetration – by enzymatic degradation (e.g. Powdery mildews). Many plant pathogenic fungi secrete a cutinase enzyme (cutin –major structural protein of cuticle) – and can degrade some polysaccharides of fungal walls (hemicelluloses, cellulose, lignin).

GERMINATION AND PENETRATION OF PATHOGENS

Rust Downy mildew

Botrytis sp.

Powdery mildew

HOST PLANT COLONIZATION

After penetration to host cell this cell may die immediatelly or can live (biotrophic pathogens)

Formation of HAUSTORIA (involved in nutrient uptake)

Normally the plasmalemma of the host cell is not broken, but forms an invagination so that the hypha is still topologically on the outside of it.Haustorium have an important role in the transfer of substances between host and fungus.

Other possibility of nutrient supply - throught intercellular mycelium (Claviceps sp.)

INTERCELLULAR OR EXTRAMATRICAL MYCELIUM - for spreading of pathogen

DISSEMINATION OF PATHOGEN – on plant surface

RESISTANCE MECHANISMS OF PLANTS

PRE-FORMED HOST RESISTANCE STRATEGIES

Structural barriers

Thick wax or cuticle layer covering the epidermis

Thick cell walls – highly lignified walls

Size, shape and location of stomata

Hairs on leaf surface

Metabolic barriers

Low content of essential pathogen nutrients

Pre- formed fungitoxic compounds (saponins of oats and tomato)

RESISTANCE MECHANISMS OF PLANTS II.

INDUCED DEFENCE STRATEGIESDefence mechanisms that develop in response to infection

1. OXIDATIVE BURST, general reaction of plant cells to trauma –involved a rapid production of hydrogen peroxide

2. HYPERSENSITIVE REACTION –This is a rapid death of a few cells at the point of invasion, followed by cessation of fungal invasion –visually visible as a spots. It is common response in race-specific resistance (biotrophic relationship cannot be established). HR involves a genetically programmed suicide of the cells surrounding the infecting fungus and both O2

- and H2O2 production (Oxidative burst) may participate in this response HR is particularly debilitating to biotroph, hemibiotroph pathogens, that require living plant tissue to survive)

Hypersensitive reponse of tomato leaf tissue as reaction on attack of powdery mildew

PAPILAE – a localized thickening of the host wall where a hyphae penetrates a cell (presence of callose, lignin, suberin). Non-adapted pathogens may be inhibited.

TYLOSES – formed in xylem vessels as a response to abiotic stress – protoplasts from the surrounding xylem parenchyma cells extend and protrude into the xylem throught pits – blocking pathogen advancement through the vascular system.

Formation of papilae after penetration of germ tube of powdery mildew

5. MORPHOLOGICAL CELL WALL ALTERATIONS - e.g. lignification, suberinization – formation of lignin in cell walls (lignin increase the resistance of cell walls to penetration and degeneration)

6. FORMATION CALLUS AND CORK CELLS AROUND INFECTION7. PRODUCTION OF PHENOLICS AND PHYTOALEXINS.

Phytoalexine – low molecular weight compounds formed locally in plant cells in response to fungal invasion – it inhibit fungal growth

8. PRODUCTION OF FUNGAL – DEGRADING ENZYMES (chitinases, glucanases) AND DETOXIFICATION OF PATHOGEN TOXINS

9. LOCALIZED AND SYSTEMIC ACQUIRED RESISTANCE -resistance that develops in plants at a distance from the initial infection point. Weakly pathogenic fungus or a non-compatible pathogen can cause the plants to acquire resistance to subsequent challenge by a compatible pathogen – oxidative burst, increasing activities of PR-proteins.

CONTROL OF FUNGAL DISEASES

1. CULTURAL PRACTISES – quarantine, crop rotation (effective only if the resting stage persist for a single winter (problem in Synchytrium endobioticum), crop hygiene

2. FUNGICIDES - abiotic (sulphur, copper), contact, systemic

3. BREEDING RESISTANT LINES –

4. BIOLOGICAL CONTROL – use of living organisms or their products (e.g. Bacillus subtillis, Pseudomonas, Trichoderma harzianum, (antibiotics, mycoparasitism), Gliocladium, Ampelomyces quisqualis

5. INTEGRATED CONTROL – combination of all methods

MAJOR GROUPS OF PLANT PATHOGENIC FUNGI

1. Biotrophic pathogens

2. Necrotrophic pathogens

1. Damping off, root rot pathogens

2. Pathogens on ripening fruits and fleshy tissues

3. The vascular wilts pathogens

4. Leaf and stem spots and anthracnose

5. Tree parasites

1. BIOTROPHIC PARASITES Parasite and host live together for longer periods of time Dependent on living tissues Most biotrophic fungi are obligatory parasites Do not produce large quantities of extracellular cell wall degrading enzymes or toxins. There is little or no immediate cell death. They have limited host range (host and organ specificity). They survive only limited saprophytic phases; especially the development of a fruiting body is dependent on the presence of a host The cultivation of single (vegetative) stages of these fungi in cell-free nutrient medium succeeded only in a few exceptions.

Extracellular biotrophs Downy mildews (Peronosporales)Powdery milews (Erysiphales)Rusts (Uredinales)Smuts (Ustilaginales)Taphrinales Intracellular biotrophsPlasmodiophora brassicae, Spongospora subterranea(Plasmodiophoromycota)Olpidium sp. (Chytridiomycota)

DOWNY MILDEWS

OOMYCOTA Biotrophic parasites with high host specificity Mostly with intercellular mycelium and haustoria in attacked cells. On the host surface forming sporangiophores with sporangia bearing zoospores Many parasitic oomycetes attacking land plants show adaptation of a zoosporangium to their life as terrestrial parasites. Sporangia break away and are dispersed whole, like large conidia (germinate directly by germ tube).

PERONOSPORALES

Plasmopara viticola, Vřetenatka révováBremia lactucae Plíseň salátováPseudoperonospora cubensis Plíseň okurkováPeronospora destructor Plíseň cibulováAlbugo candida Plíseň bělostná

Life cycle of Plasmopara viticola

Plasmopara viticola on Vitis vinifera

Sporangiophores and sporangia

Bremia lactucae symptoms of disease

Bremia lactucaesporangiophores

Pseudoperonospora cubensis, symptoms of disease on cucumber leaf

Pseudoperonospora cubensis sporangiophores and sporangia

Peronospora destructorsporangia a sporangiophores

Peronospora destructor

symptoms of disease on onion leaf

Albugo candida Symptoms on Capsella bursa-pastoris

Cross section of plant attacted by Albugo candida

POWDERY MILEWS

ORDER ERYSIPHALES, ASCOMYCOTINA

They are biotrophic parasites

Mostly with white superficial mycelium, which penetrate to the host cells with haustoria.

On the leaf surface forming conidiophores with conidia and at specific environmerntal conditions also teleomorph stage -cleistiothecia

Life cycle of Podosphaera leucotricha

Germinating conidium

Cleistothecium with one ascus

Conidiophores and superficial mycelium

Apendixes on cleistothecia

Microsphaera Uncinula

POWDERY MILDEWS, ASCOMYCOTINA

Sphaerotheca mors-uvae

Sphaerotheca fusca (Podosphaera xantii) –Blumeria graminis

Taphrina betulina –witches broom on birch

Taphrina deformans on leaves of peach

Taphrina pruni on plum fruit

TAPHRINALES ASCOMYCOTINA Cause deformation and stunting (hypertrofy, hyperplasy) of leaves and branches (witches broom). Caused by growth hormones (auxins) liberated by the pathogen

UREDINALES (RUSTS)

BASIDIOMYCOTINA

Uredinales include about 4,000 species in 100 genera.

They are characterized by the red-brownish colour (rusts) of their spores.

Rusts develop haustoria and infect a range of angiosperms, gymnosperms, and pteridophytes.

Puccinia graminis is the classic example of a fungus with an alteration of hosts. Its haploid (monocariontic) mycelium grows on Berberis (barberry), its dicariontic mycelium on different grasses. P. graminis is characterized by a complex alternation of generations. Up to five different types of spores can be generated during its course.

Life cycle of Puccinia graminis

Types of spores:basidiospory spermacie aeciospory urediospory teliospory

Spermogonia with spermacia

Aecia with aeciospores

Uredia with uredinospores

Telia with teliospores

UREDINALES

Puccinia graminis – aecia on Berberis sp.

Puccinia graminis –teliospores

Cronartium ribicola – on Ribes sp.

Cronartium ribicola –aecia on Pinus strobus

Gymnosporangium sabinae, aecia on Pirus sp.

Gymnosporangium sabinae, telia on Juniperus sp.

USTILAGINALES (SMUTS)

More than 1000 species of Ustilaginales live parasitically on hosts of more than 75 angiosperm families.

They produce dark, powder-like traces consisting of fruiting bodies strung together on leaves, shoots, flowers, and fruits.

They develop usually no haustoria.

Their extensive mycelium spreads through the intercellular spaces of the host plants.

Life cycle of Ustilago tritici

promycel

Basidie (sporidie)

Chlamydospory (Teliospory)

Ustilago tritici –chlamydospores (teliospores)

Ustilago tritici, symptoms

USTILAGINALES

Ustilago maydis, on Zea mays

Ustilago segetum, on barley

BIOTROPHIC PARASITES –INTRACELLULAR

PLASMODIOPHOROMYCOTA Obligate parasites of high plants, algae and fungi Forming paraplasmodia in host cellsWhole plasmodium transfered into sporangium

Life cycle of Plasmodiophora brassicae

Resting spores of Plasmodiophora brassicae

Roots of Brassica spp. attacked by Plasmodiophora brassicae

zoospores

Sporangia in root cells

Olpidium brassicae, caused necrosis of hypocotyl at seedlings of Brassicaceae

INTRACELLULAR BIOTROPHIC PARASITES

CHYTRIDIOMYCOTA

Synchytrium endobioticum,

Germinated prosorus

2. NECROTROPHIC PATHOGENS

2. A. DAMPING OFF, ROOT ROT PATHOGENS

DAMPING OFF – soft watery rot of parenchymatous tissue attached pectic substances in the middle lamella between cell.

They include Pythium spp. which attack the emerging root tips

Rhizoctonia solani, which characteristically attacks the young shoot base

Sclerotium rolfsii which attack basal stem tissues

Fusarium spp. which are seed-rot and seedling patogen.

All these fungi grow rapidly in soil wet conditions and can ovelhelm the host in a short time.

Their host range is characteristically wide, because they exploit tissues that do not exhibit the major defence mechanisms that vary between plant types.

Pythium sp., cause damping of young plants

Sporangium of Pythium sp.

Sclerotium rolfsii on stem base of tomato Rhizoctonia solani - rot

of cabbage

Fusarium root rot

Fusarium spp. conidia

2. NECROTROPHIC PATHOGENS

2. B. PATHOGENS ON RIPENING FRUITS

Ripening fruits and other fleshy plant tissues can be rotted rapidly by pathogens in appropriate conditions.

All these pathogens caused rots by pectic enzymes which degrade the middle lamella, or cementing layer between plant cell walls.

Botrytis cinerea – causes grey mould of soft fruits such as strawberries, raspberries, grapes. Initiated growth on senescing flower remains and then invade the living tissue of the ripening fruit

Penicillium italicum, P. digitatum – which rot citrus fruits,

Penicillium expansum – rots apples (produce mycotoxin)

Monilia fructigena – rots apples, pears, peaches.

Last three are wound pathogens – enters through wounds

Botrytis cinerea , teleom. Botrytionia fuckeliana on grapes

Conidiophore with conidia Botrytis cinerea

Botrytis cinerea on strawberry fruit

Penicillium italicum and Penicillium digitatum on Orange

Penicillium expansum on apple fruit

Conidiophores with conidia of Penicillium expansum

Monilia fructigena, teleom. Moniliniaon apple fruits

Coniophores with conidia of Monilia fructigena from an infected apple.

2. NECROTROPHIC PATHOGENS2. C. THE VASCULAR WILT PATHOGENS AND OTHER ENDOPHYTES

Vascular wilt pathogens cause some of the most devastating plant diseases

Vascular pathogens can cause cell death by production of toxins (fusaric acid) and also cause cell death indirectly, by obstructing the flow of liquid in the xylem vessels and tracheids (Fusarium oxysporum, Ophiostoma ulmi). The vessels become blocked with hyphae and spores, fungal polysaccharides, or tyloses (produced by parenchymatous cells of plants)

Systemic colonization of xylem leads to various symptoms such as yellowing and necrosis of the leaves, wilting and eventual death of the plant (often toxins have been implicated in vascular wilt)

Caused by species of Fusarium oxysporum and Verticillium albo-atrum (Hyphomycetes) and Ophiostoma (Ascomycetes)

Enter via wounds or through the cortex of the young root region before the endodermis has deveoped

Conidia

Fusarium wilt symptoms on tomato

Cut through a sunflower stem showing Verticillium wilt microsclerotia

Verticillium wilt on tomatoes

Ophiostoma ulmi Dutch elm disease

Perithecium of Ophiostoma ulmi with mycelium

2. NECROTROPHIC PATHOGENS

2. D. LEAF AND STEM SPOTS AND ANTHRACNOSE

Occurrence of localized lessions on host leaves and stems

Caused mainly by representatives of Deuteromycotina

Leaf and stem spots (Septoria, Cercospora, Ascochyta, Mycosphaerella), anthracnose (Colletotrichum)

Cercospora beticola Skvrnatička řepná

Mycosphaerella fragariae on strawberry leaves

Colletotrichum lindemuthianumon bean husk

Septoria apii on celery leaves

2. NECROTROPHIC PATHOGENS

2.E. PARASITES OF TREE

Tree are often killed by necrotrophic parasites Wound parasites – Piptoporus betulinus, Polyporus

squamosus – only on weakened trees Some fungi can kill healthy undamaged tree - Armillaria

mellea, Heterobasidion annosus. Penetrating to tree via roots. They may grow also as a saprophyte on the dead stumps of its victims.

Armillaria mellea continued to live saprophytically on the wood after killing the tree

Heterobasidion annosum

Aggressive parasite that infects cut stumps, spreads from root system to root system, and kills many different conifers

FUNGAL PARASITES OF ALGAE

MARINE WATER

More than 200 filamentous marine fungi have been described. Between a quarter or a third of them live parasitically on algae. Most of them belong to the Ascomycetes. Brown, red, and green algae as well as diatoms serve as their hosts.

FRESHWATER

Most parasites of freshwater algae belong to the chytrids. Chytrids are simple, non-mycelian fungi, reproduction by zoospores that find host by chemical cues.

FUNGAL PARASITES OF ALGAE - CHYTRIDIOMYCOTA Develop no hyphae, but a non-cellular and partially rather extensive system of rhizoids that seizes the host cells and can even enclose them. Nearly every known species of algae has its own specific parasite. The fungus infections should not be underestimated. Infections of nearly all algal cell-colonies have often been observed towards the end of a ‘water bloom’, i.e. the massive growth of an algal species. Chytrids infect both blue-green algae (Cyanophyceae) and green algae (Volvocales, as well as Chlorococcales). These groups of algae differ in the chemical composition of their cell walls so that the respective parasites have to have the most diverse enzyme systems at their disposal. The destruction of a cell occurs only after a cell-to-cell contact has been established, i.e. the fungus secretes no lytic substance into the adjacent medium that destroys all cells of a colony that are surrounded by a gelatinous coat.

Rhyzophydium sp.attached Chlamydomonas

Rhyzophydiumsp. attacking Spirogyra sp.

Rhyzophydium sp.Sporangia on a moribund filament of Oedogonium

Chytridium versatilefungal parasite on Diatomas

Polyphagus euglenae on Euglena

Phlyctidium scenedesmi, on Scenedesmus

FUNGAL PARASITES ON OTHER FUNGI Mycoparasitism – about 3000 fungal species is parasitic on other fungi Some mycoparasites are BIOTROPHS. Most biotrophic mycoparasites are members of Zygomycotina (Piptocephalis). They absorbe nutrients from living host cells and have more narrow host range. NECROTROPHIC MYCOPARASITES (kill tissue of host)– include some Deuteromycotina (Trichoderma, Gliocladium roseum), which have wide range of hosts and Oomycetes Pythium, Zygomycetes Spinellus.

The attack may be physical (with the hyphae of one mycelium penetrating the hyphae of the other mycelium) or chemical (with the hyphae of one mycelium producing chemicals to dissolve the hyphae of the other mycelium) - or a combination of the two. When the host is itself a parasite, such fungi are termed HYPERPARASITES – e.g. Ampelomyces quisqualisMacrofungi which parasitize other macrofungi (Boletus parasiticus on Scleroderma citrinum) – is not easy recognise if they are biotrophs or necrotrophs Some of mycoparasitic fungi is used in biocontrol of other fungi –Trichoderma against Sclerotinia, Botrytis, Fusarium.

FUNGAL PARASITES OF OTHER FUNGI – CHYTRIDIOMYCOTA

Some chytrids parasitize water moulds or other chytrids

Rhizophidium chytriophagum sp.

Pythium oligandrum (Po) parasitize on Botrytis cinerea (Bc). This species has been found also in spores of mycorrhizal fungus Glomus macrocarpum.

FUNGAL PARASITES OF OTHER FUNGI - OOMYCOTA

Appressorium (ap) and a branched haustorium of the mycoparasite Piptocephalis unispora (Zoopagales, Zygomycotina) in a fungal host, Cokeromyces recurvatus

Piptocephalis, parasite of other members of Mucorales

FUNGAL PARASITES OF OTHER FUNGI - ZYGOMYCOTINA

FUNGAL PARASITES OF OTHER FUNGI - ZYGOMYCOTINA

Mycena sp., has been attacked by a parasitic fungus called Spinellus fusiger

Cordyceps capitata The fungus is widespread but not common and parasitizes an underground fungus called Elaphomyces.

Cordyceps ophioglossoides This taxon also parasitizes sp. of Elaphomyces

FUNGAL PARASITES OF OTHER FUNGI – ASCOMYCOTINA

Hypomyces lactifluorum (Bysonectria viridis, Hypocreales), parasitize on Russulales (Russula, Lactarius)

Perithecia

FUNGAL PARASITES OF OTHER FUNGI – ASCOMYCOTINA

Coiling of Trichoderma hyphae around the plant pathogen Rhizoctonia solani

FUNGAL PARASITES OF OTHER FUNGI - DEUTEROMYCOTINA

Trichoderma produce antibiotics active against fungi or bacteria – inhibit growth of Pythium, Rhizoctonia, also secrete chitinase and glucanase.

Infection of conidia and germ tubes for Botrytis cinerea (BC) by Gliocladium roseum (GR)

FUNGAL PARASITES OF OTHER FUNGI - DEUTEROMYCOTINA

Ampelomyces attacks many powdery mildew fungi. It forms appressoria on the spores and hyphae of its hosts and penetrates them, extending from cell to cell

Pycnidium of A. quisqualiswhich has formed in place of a conidium atop the conidiophore of Uncinula necator

FUNGAL PARASITES OF OTHER FUNGI - DEUTEROMYCOTINA

Xerocomus parasiticus .Found only as a parasite of the Scleroderma citrinum.

FUNGAL PARASITES OF OTHER FUNGI – BASIDIOMYCOTINA

Asterophora parasitica. Obligate agaric parasites of agarics (Russulas in particular))

HYPHAL INTERFERENCE

Several basidiomycotina antagonize other fungi, including other basidiomycotina, in contact.

It occurs a few minutes after hyphal contact. The first visible sign is localized vacuolation and loss of turgor – it leads to loss of membrane integrity.

It does not seem to be parasitic mechanism because the aggressor hyphae does not enter the damage hyphae – inactivate other hyphae (as a potential competitors for the same substrates)

Hyphae of Heterobasidion annosum (previously termedFomes annosus) have been antagonised where they were contacted by single hyphae ofPhlebiopsis gigantea(previously termed Peniophora gigantea)