Transcript Plant Pathogen Groups

Abiotic vs. Biotic Plant Problems
Discuss:
•Abiotic Plant Problems
•Biotic Plant Problems (Plant Diseases)
•Disease Triangle
•Plant Pathogens: Bacteria, Fungi,
Oomycota, Viruses, Viroids,
Nematodes
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Photos used from various UF/IFAS Extension Publications or provided by UF/IFAS faculty and staff, unless otherwise stated
Abiotic Plant Problems
Abiotic plant problems are caused by
environmental factors, either natural or man-made
non-infectious, non-living (abiotic = without life)
• Unfavorable soil properties or structure
• Nutrient imbalances
• Moisture extremes
• Temperature extremes
• Light extremes
• Physical injuries
• Chemical toxicity
• And in Florida, lightning strikes!
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Abiotic Human Problems
• Vitamin deficiencies
• Cholesterol imbalances
• Mercury or lead poisoning
• Broken bones
• Burns
• Allergic Reaction
• Others?
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Abiotic Plant Problems
• Can kill plants
• Can predispose plants to infection by plant
pathogens
• Can be natural, such as temperature extremes
• Can be due to human activity, such as improper
use of fertilizers or pesticides
• It is common to have both biotic and abiotic
problems affecting plant at same time,
independently!
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Abiotic: Physical Injuries
• Lightning strikes
• Car or lawn equipment exhaust
• Animals - moles, armadillos, urine
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Abiotic: Cold Temperatures
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Abiotic: Plants can be sunburned
too – not just tourists!
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Abiotic: Excess Water
Oedema: little pimples form
on leaf; roots taking up water
faster than plant can use or
transpire
T. Broschat, UF/IFAS/FLREC
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Abiotic: Low Soil Moisture
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Abiotic: Nutrient Deficiency
Tomato: Calcium
Sunflower: Iron
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Palm: Potassium
Celosia: Manganese
Citrus: Zinc
Palm: Manganese
Photos from various UF/IFAS Extension Publications
Abiotic: Chemical Damage
Herbicide damage
Herbicide damage
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Excessive iron chelete applied to soil
Biotic Plant Problems
Biotic plant problems or diseases
require a second organism that will
infect the plant and disrupt its
normal appearance and growth –
infectious, living
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Plant Disease Triangle
Susceptible Host
• Immunity or resistance is the rule for plants
• Some plant pathogens are very host
specific; others have a wide host range
Pathogen
• Pathogens are not found “everywhere”
Favorable Environment
• All the environmental factors surrounding
the host and pathogen may help the
pathogen infect the host and determine the
severity of disease development.
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Plant Disease Triangle
Susceptible
Host
DISEASE
Favorable
Environment
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Pathogen
Plant Disease Triangle
Susceptible
Host
X
NO
Pathogen
Disease
X
NO
Disease
Favorable
Environment
Favorable
Environment
Pathogen
X
NO
Disease
Favorable
Environment
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Pathogen
Plant Pathogens
•Fungi
•Oomycetes
•Bacteria (including fastidious
bacteria)
•Viruses and Viroids
•Nematodes
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Fungi and Oomycetes
• Oomycetes used to be considered a family
within the Kingdom Fungi
• Fungi now considered more closely related
to animals than Oomycetes
• Oomycetes now considered more closely
related to plants and algae
• Both fungi and Oomycetes are eukaryotes
that digest food externally and absorb
nutrients directly through their cell walls
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Fungi and Oomycetes
Life styles:
• Heterotroph: obtain carbon and energy from
other organisms
• Biotroph: obtain nutrients from living host
• Saprotroph (saprophyte, saprobe): obtain
nutrients from dead host
• Nectrotroph: infect a living host, then kill host
cells to obtain nutrients
• Obligate: can only grown in association with
its host plant (can’t grow on artificial media)
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Fungi and Oomycota
Character
Sexual reproduction
True Fungi
Oospores not produced;
Heterogametangia;
Sexual reproduction
Fertilization of oospheres
results in zygospores,
by nuclei from antheridia
ascospores or
forming oospores.
basidiospores
Nuclear state of
vegetative mycelium
Diploid
Haploid or dikaryotic
Cell wall composition
Beta glucans, cellulose
Chitin; cellulose rarely
present
Type of flagella on
zoospores, if produced
Mitochondria
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Oomycota
Two types; one whiplash,
directed posteriorly; the
other fibrous, ciliated,
directed anteriorly
With tubular cristae
If flagellum produced,
usually of only one type:
posterior, whiplash
With flattened cristae
From: Why are Phytophthora and other Oomycota not true Fungi? By Amy Y. Rossman and Mary E. Palm
http://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages/Oomycetes.aspx
Also see: http://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages/IntroOomycetes.aspx
Oomycota
Phytophthora:
• Zoospores emerging from sporangium
https://www.youtube.com/watch?v=lB4QYN7dlgc
• Zoospores attracted to root exudates
and infecting the root
https://www.youtube.com/watch?v=PxF8OwDtJh0&ebc=ANyPxKrXPjQG4MBmaGz5uf5WqgjD3b5370YlqKjvvIxp1IOGGJso3YgDPyd2RI
8niluJ1hxA-ALaRk9ZdlDQk2P3tGWEQXIkw
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Oomycota
Diseases caused by Oomycetes:
• Root rots of numerous plants
Pythium spp.
• Late blight of potato and tomato
Phytophthora infestans
• Downy mildew of grape and impatiens
Plasmopara viticola – grapes
Plasmopara obducens – impatiens
• Sudden oak death (Ramorum blight)
killing oak species in CA
Phytopthora ramorum
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True Fungi
Fun Fungal Factoids:
• About 99,000 known fungal species, and we
add about 1,200 each year
• Most plant diseases (70%) are caused by fungi
• But, fewer than 10% of the known fungi cause
plant diseases
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True Fungi
Fun Fungal Factoids:
• Plant pathogenic fungi are parasites, but not all
plant parasitic fungi are pathogens!!
• Parasite obtains nutrients from a living host plant
 If causes disease with symptoms (disrupts
normal growth and appearance of plant),
parasite is a pathogen
 If simply depends on plant host for
nutrition, parasite is either a beneficial
symbiont or an endophyte
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True Fungi
Fun Fungal Factoids:
• Endophyte example:
• Neotyphodium (Ascomycota) – beneficial
for landscape grasses (heat and water
stress) but not beneficial for pasture grasses
as fungus produces alkaloids that are bad
for animals
• Beneficial symbiont examples:
• Mycorrhizae – root/fungal association
• Lichen – algal/fungal association
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True Fungi
Main fungal groups (phyla):
• Ascomycota
• Basidiomycota
• Chytridiomycota
• Zygomycota
• Glomeromycota (arbuscular
mycorrhizae)
• Sixth one may be added
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http://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages
/IntroFungi.aspx
True Fungi
Four phyla with plant pathogens:
• Ascomycota – most plant pathogens
• Basidiomycota – Rusts, Smuts and Rotters
• Chytridiomycota – pathogens and vectors of
plant viruses
• Zygomycota – Mucor, Rhizopus – post-harvest
diseases of fleshy fruits and vegetables
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Ascomycota
Fungi and Sex and Names
• If a fungus is reproducing without sex, spores produced
are asexual spores = conidia, which come in all different
sizes, shapes and colors
• If fungus is reproducing with sex, spores produced are
sexual spores = ascospores
• Ascospores are produced in a saclike structure called an
ascus
• Fungi often have two Latin names – one for the asexual
stage and one for the sexual stage
• Some fungi only produce conidia; some fungi only
produce ascopsores; some fungi produce both
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Ascomycota: Sexual Spores
By Beth Des Jardin, UF/IFAS, FLREC
By CarmelitaLevin - Own work, CC BY-SA 4.0,
https://commons.wikimedia.org/w/index.php?curid=41198109
By CarmelitaLevin - Own work, CC BY-SA 4.0,
https://commons.wikimedia.org/w/index.php?curid=41198837
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Sordaria asci and ascospores
By Beth Des Jardin, UF/IFAS, FLREC
Serenomyces asci and ascospores
Ascomycota: Asexual Spores
Pestalotiopsis
Phomopsis
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Lasiodiplodia
Fusarium
All photos by Beth Des Jardin, UF/IFAS, FLREC
Exserohilum
Cylindrocladium
Basidiomycota
(Rusts, Smuts and Wood Rotters)
Rusts
• can produce up to 5 different spore types
• can complete life cycle on one host, or some
complete their life cycle on two hosts
• devastating diseases that humans have dealt with
since they started cultivating crops (wheat, etc.)
• we are still trying to manage these diseases,
primarily by breeding for resistance
Life cycle of wheat stem rust
https://www.youtube.com/watch?v=AeuP5IYP5HA
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Basidiomycota
(Rusts, Smuts and Wood Rotters)
Smuts
Ustilago maydis
Corn Smut
Huitlacoche
Ustilago nuda
Loose Smut
By Boom10ful (Own work) [CC BY-SA 4.0 (http://creativecommons.org/licenses/
by-sa/4.0)], via Wikimedia Commons
Tilletia indica
Karnal Bunt
basidiospore
By Rasbak (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html)
or CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via
Wikimedia Commons
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Jim Plaskowitz, USDA/ARS, Public Domain
Basidiomycota
(Rusts, Smuts and Wood Rotters)
Wood Rotters
Ganoderma zonatum
Ganoderma Butt Rot
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Armillaria tabescens
Armillaria Root Rot
Chytridiomycota
• include pathogens and a vector of a plant virus
• obligate fungi
By USDA-APHIS-PPQ - USDA-APHIS-PPQ Agence canadienne d'inspection des aliments,
Public Domain, https://commons.wikimedia.org/w/index.php?curid=5603175
Synchytrium endobioticum
Black Wart Disease of Potato
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Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org
Olpidium brassicae transmits a
virus that causes Lettuce Big Vein
Bacteria
 Bacteria
• do not cause nearly as many diseases as fungi
or viruses
• plant pathogens include both gram-positive and
gram-negative bacteria
• easily grow on artificial media
• many species are subdivided into pathovars,
indicating distinctive pathogenicity to one or
more plant hosts
http://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages/Bacteria.aspx
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Bacteria
 Fastidious Bacteria
• all are vascular colonizers vectored by insects
• very difficult to grow artificially, if at all
• group without cell walls:
 phytoplasma – phloem-limited; Candidatus
Phytoplasma palmae
 spiroplasma – phloem-limited; Spiroplasma
kunkelii
• group with cell walls:
 phloem-limited bacteria - Candidatus Liberobacter
asiaticum (=Huanglongbing pathogen)
 xylem-limited bacteria - Xylella fastidiosa
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http://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages/Fastidious.aspx
Bacteria
•Fastidious bacteria are
very small
Spiroplasma
Phytoplasma
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Xylella
Viruses
• are non-cellular; assemble themselves
• mature virus particles are dormant
• they come “alive” and reproduce only inside
infected cells – obligate parasites
• virus particles (virions) composed of:
 genome (nucleic acid) – ss+RNA,
ss-RNA, dsDNA
 protein protective shell (capsid)
 some enveloped within lipoprotein
membrane
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http://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages/PlantViruses.aspx
http://plantpath.ifas.ufl.edu/plant-virus-profiles/#
Viruses
• range from 30 nm diameter (spherical viruses)
to 2 µm (filamentous viruses)
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McGraw-Hill Concise Encyclopedia of Bioscience. S.v. "Plant viruses and viroids." Retrieved May 21 2016 from
http://encyclopedia2.thefreedictionary.com/Plant+viruses+and+viroids
Viruses
• immobile – rely on other organisms to be moved
around from plant to plant
• passive transmission – mechanically, vegetative
propagation (cuttings) or seed
• active transmission requires vector
 plant-feeding arthropods, especially aphids
and whiteflies
 nematodes
 plant-parasitic fungi
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Viroids
• naked, infectious RNA – no protein coat
• genomes between 246-375 nucleotides
• do not produce any proteins when they
infect a plant cell
• use the host cell RNA polymerase to
reproduce their RNA and move into other
plant cells
• spread through vegetative propagation,
mechanical contamination, pollen and
seed; vectors not necessary
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http://www.apsnet.org/publications/apsnetfeatures/Pages/Viroids.aspx
Viroids
• They may be small, but the diseases can still
be devastating!
• Cadang-Cadang is a viroid disease of coconut
palms that has destroyed over 30 million
palms in the Philippines
• Potato spindle tuber viroid is model pathogen
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http://www.apsnet.org/edcenter/intropp/lessons/viruses/Pages/PotatoSpindleTuber.aspx
Nematodes
• are roundworms (multicellular animals)
• most are free-living (40%) – feed on
bacteria, fungi, protozoans and other
nematodes
• but, many are parasites of animals (44%)
and plants (15%)
• need water (even if minimal)
• Caenorhabditis elegans – bacterialfeeding nematode (not plant parasitic)
http://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages/IntroNematodes.aspx
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http://www.apsnet.org/EDCENTER/K-12/NEWSVIEWS/Pages/Nematodes.aspx
Nematodes
• Plant Parasitic Nematodes:
 have a hollow mouth spear called a stylet
 stylet connected to pharynx, which is
connected to the intestine
 stylet used to puncture plant cells, withdraw
food, and secrete protein and metabolites that
aid the nematode in parasitizing the plant
Nematode
Endoparasitic
Human Hair
Ectoparasitic
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Bacteria, Fungi, Oomycota,
Viruses, Viroids, Nematodes
Which Plant
Pathogen
Are YOU?
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Which Plant Pathogen Are You?
is a "personality quiz" aimed at
engaging audiences and creating
awareness about plant pathology.
It can also be used as an icebreaker or classroom activity.
This is based on the American Society for Microbiology's
educational activity, What Microbe Are You? A full lesson
plan for the ASM activity can be found online:
www.asm.org/index.php/educators/k-12-classroomactivities/23-education/k-12-teachers/8214-what-microbeare-you
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Which Plant Pathogen Are YOU?
#16 I am . . .
Phytophthora capsici
Spots, rots and blights
I am a fungus-like pathogen
(oomycete) that loves my
fruits and veggies - except
lima beans.
Wet, humid conditions help
me thrive. I can cause seed
rots, seedling blights, leaf
spots, fruit rots – look at this
zucchini:
Photo: UF/IFAS, PP176
Oomycota
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Electronic Data Information System (EDIS)
http://edis.ifas.ufl.edu
Which Plant Pathogen Are YOU?
#16 I am . . .
Phytophthora capsici
Spots, rots and blights
I am a fungus-like pathogen
(oomycete) that loves my
fruits and veggies - except
lima beans.
Wet, humid conditions help
me thrive. I can cause seed
rots, seedling blights, leaf
spots, fruit rots – look at this
zucchini:
Photo: UF/IFAS, PP176
Oomycota
• 30 cards, each with a
different pathogen
• Many, but not all, have
an EDIS document that
a you can refer to for
more information
• EDIS publications are
reviewed at least every
3 years to keep the
information up to date
• Photos can be used from EDIS documents, but please
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acknowledge the source.
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