plant pathogenesis fungi

PLANT PATHOGEN

FUNGIApple cedar rustBy Hikmal, Ain, Sabrina,

Fatihah

• Disease cycle similar to virus and bacteria• Can not only penetrate host via wounds or

natural opening, they can also actively penetrate via production of appresoria – allows direct penetration through mechanical and enzymatic activity

PATHOGENIC FUNGI

Appresoria – swollen tips of hyphae

FUNGALLIKE ORAGANISMS (FLO) TRUE FUNGI

IMPERFECT FUNGI

With walls containing chitin, and with many

other cellular and biochemical features

With fungal lifestyle but with cellulose walls and

with cellular and biochemical features

resembling those of plants

With fungal-like structures, but grow as wall-less protoplasmic

stagesAcrasids, Myxomycetes,

PlasmodiophoridsZygomycota, Ascomycota, Basidiomycota

Oomycota

• Extremely destructive fungal disease of potatoes – attack both tubers and foliage at any stage

• a serious pathogen on tomatoes in cool, wet climates

OOMYCOTALate blight/Potato

blightPhytophora infestans

•Appearance of dark necrotic lesions within 3 to 5 days of initial infection on leaves•Dark, water-soaked lesion on petioles and stems•Lesion axpand when P. infestans colonizes internal plant tissues•On mature lesions, P. infestans produce sporangia – underside of the leaves/surfaces of stem•As disease progress, the entire plant becomes blight and decay

SYMPTOMS

Disease cycle

Blight infection on leaf petiole

Infected green fruit

• Disease that affects both annual and perennial crop species in the legume family

• Aphanomyces – root-infecting oomycetous fungi, present in wet and poorly drained soils

Aphanomyces Root Rot (ARR)Aphanomyces euteiches

a) Infected root b) Healthy root

Yellowing due to Aphanomyces

SYMPTOMS•infected root tissue appears gray

and water-soaked, becoming soft and honey-brown or blackish-brown in appearance•roots are reduced in volume and function•Primary symptoms of roots and stems will eventually lead to secondary symptoms of chlorosis, necrosis, and wilting of the foliage

DISEASE CYCLE

Diseased caused by Plasmodiophoromycetes

Three genus of Plasmodiophoromycetes that known to cause following diseases:

◦ Plasmodiophora: causing clubroot of crucifiers◦ Polymyxa : causing a root disease of cereals and grasses◦ Spongospora: causing the powdery scab of potato

The most common disease : Clubroot of crucifiers

Clubroot of Crucifers The clubroot disease of cruciferous plants such as cabbage and cauliflower is widely distributed all over the world

◦ Cruciferous plants: or also term as cruciferous vegetables are vegetables of the family Brassicaceae, are widely cultivated such as cauliflower, cabbage, broccoli, brussels sprouts and similar green leaf vegetables. This group of vegetables was originally named for the four-equal sized petals in its flower. They are also known as cole crops.

Fields once infested with the clubroot pathogen remain so indefinitely and become unfit for cultivation of crucifers

Symptoms Infected plants at first have pale green to yellowish leaves

Wilting in the middle of hot sunny days

Young plants may be killed by the diseases

Older plants may remain alive but become stunted

The roots of infected plants: appear on the roots as spindle-like, spherical, knobby or club-shaped swelling

The swelling may be few and isolated or they may coalesce and cover the entire root system

Source: http://www.cals.ncsu.edu/course/pp728/ Plasmodiophora/Plasmodiophora.html

Source:http://www.omafra.gov.on.ca/IPM/english/brassicas/diseases-and-disorders/clubroot.html

Figure 1:Clubroot on infected roots

Figure 2: Clubroot on Brussels sprout

The pathogen: Plasmodiophora brassicae

Obligate parasites

Can survive in the soil as resting spores for many years

Plasmodium-shaped body

The plasmodium gives rise to zoosporangia or to resting spore which on germination produce zoospores

The plasmodium lives off the host cells it invades but does not kill these cells for a long time

The pathogens spread from plant to plant by means of zoospores, by anything that moves soil or water containing spores-soil borne fungus

Development of Disease

Control actions Avoid growing cruciferous crops in fields known to be infested with the clubroot pathogen

Plant the cruciferous vegetables in well-drained fields that have a pH slightly above neutral (pH 7.2) or in fields in which hydrated lime has been added to raise the soil pH

Treat the soil with chloropicrin, methyl bromide or metam sodium approximately 2 weeks before planting

-Contain fungi called zygomycetes-Live in soil or on decaying plant- The hyphae of zygomycetes are coenocytic

- Asexual spores develop in sporangia at the tip of aeriel hyphae- Sexual reproduction produce tough, thick-walled zygotes called zygospores

- An example of zygomycetes is black bread mold (Rhizopus stolonifer)- Grow on the surface of moist, carbohydrate-rich food- Reproduce asexually but in unfavourable condition, sexual reproduction occur

Zygomycota

Structure of sporangium

Disease (Rhizopus)• Rice disease ( seedling blight)

-fungus secreted a toxin that kills rice seedling-toxin rhizoxin and rhizonan most commonly associated with this disease-lead to rapid browning and shriveling of plant tissues

ex : Rhizopus microsporus

Life cycle of rice disease fungi- starts its infection cycle when a three-

celled conidium lands on the rice leaf surface

- The spore attaches to the hydrophobic cuticle and germinates

- producing a narrow germ tube- flattens and hooks at its tip before

differentiating into an appressorium- single-celled appressorium matures

and the three-celled conidium collapses and dies in a programmed process that requires autophagy.

- The appressorium becomes melanized and develops substantial turgor

- This translates into physical force and a narrow penetration at the base

- puncturing the cuticle and allowing entry into the rice epidermis

• Rhizopus soft rot- Disease of the fleshy root in storage- Happening during packing and shipping-The disease causes a watery soft rot of the internal portion of the storage root-Gray whiskery mould with dusty black spores may grow on the fruit surfaceex : Rhizopus stolonifer

Symptoms of rhizopus soft rotDime-sized lesions are cinnamon or

chocolate-colored

A water-soaked lesion starts to develop a few

hours after the root has been wounded

The lesion becomes covered by a web-

like outgrowth

small cracks and wrinkled

appearance

emits a pleasant fermented odour that

attracts fruit flies

Disease cycle of rhizopus soft rotA combination of wet soil and low temperature at harvest time causes it susceptible to soft rot

Plant Diseases Caused by

BasidiomycetesCORN SMUT DISEASE BY USTILAGO MAYDIS

Corn smut disease Occurs wherever corn is grown- prevalent in warm and moderately dry areas

Damages plants and reduce yields by forming galls:◦ Tassels◦ Ears◦ Stalks ◦ Leaves

Figure 1: Anatomy of corn

Symptoms Minute galls form on the leaves and stems on young corn. The seedling may remain stunted or may be killed

Galls formed on young, actively growing tissue of axillary buds, individual flowers of the ear and tassel, leaves and stalk

Infected areas are permeated by the fungus mycelium-stimulates the host cells to divide and enlarge-forming galls

Galls-first covered with a greenish white membrane

Matured galls- reach size (1-15cm diameter), their interior darkens and turns into a mass of powdery, dark, olive-brown spores

The silver gray membranes then ruptures and exposes millions of teliospores-released into air

Galls on leaves: relatively small (1-2cm), hard, dry and do not rupture

Corn smut on tassel

Smut galls on an ear of sweet corn

Galls on sweetcorn

The Pathogens: Ustilago maydis

Fungus produces dikaryotic mycelium-the cells transformed into black, spherical or ellipsoidal teliospores

Teliospores germinates by producing a four-celled basidium (promycelium) from each cell of which a basidiospore (sporidium) develops

Figure 2: Ustilago maydis diploid teliospores

Development of disease

Disease caused by Fungi: Ascomycete

•Venturia inequalis•Magnaporthe grisea•Claviceps purpurea•Dibotryon morbosum

Ascomycete(Sac fungi)

• Reproduce sexually and asexually• Sexual rep: produce large

numbers of asci (in ascocarp)• Asexual rep: through vegetative

reproductive spores, the conidiaspores.

• Depending on the species they may be dispersed by wind or water, or by animals.

• Heterotrophic organisms that require organic compounds as energy sources

• secrete powerful digestive enzymes that break down organic substances into smaller molecule

Apple scab

Fungi: Venturia inequalisSymptoms: Dull black or grey-brown

lesions on the surface of tree leaves, buds or fruits. Infected leaves become yellow, then drop

Env. Cond: lack of sunlight, bad sanitation and management

Effect: Rarely kills its host, but can significantly reduce fruit yields and fruit quality

Agents: water (rain)Treatment: fungicide, good

management and sanitation

Powdery mildew

Fungi: Sphaerotheca fuligineaSymtoms: Powdery splotches of white

or gray on leavesEnv. Cond: Grows well in

environments with high humidity and moderate temperatures

Effect :Photosynthesis is impaired. Infected leaves often fall prematurely

Agents: wind, insects, water splashing Treatment: fungicide (potassium

bicarbonate), thinning and pruning, milk

Ergot

Fungi: Claviceps purpureaSymtoms: ergot that replaces the grain

of the rye is a dark, purplish sclerotiumEnv. Cond: Continuous moist

conditions, wet, cloudy and cool weather extends the period of flowering and increases the window of infection for spores to enter the florets

Effect : convulsive and gangrenous ergotism.

Agents: insects, windTreatment: fungicides, burning, insect

control, row spacing

Black knot

Fungi: Dibotryon morbosumSymtoms: Rough, black areas that

encircle and kill the infested parts. Only on the wood parts of trees, primarily on twigs and branches but can spread to larger limbs and even the trunk

Env. Cond: moderate temperaturesEffect : Destructive diseases of the

plum and cherry treesAgents: insectsTreatment: pruning infected parts

and spraying buds with a fungicide

Life cycleApple scab Powdery mildew

Ergot Black knot

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