Plant pathogenesis FUNGI
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Transcript of 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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