Download Parasitic Higher Plants - Missouri State University

Parasitic
Higher Plants
• > 2,500 Species of Higher Plants Live
Parasitically on Other Plants
• Produce Flowers & Seeds
• May or May Not Produce Chlorophyll
• May or May Not Possess True Roots
Sonja Lallemand Picture
Genera that Cause Economic Impact
to Agricultural Plants
• Cuscuta (Dodders)
• Arceuthobium, Phoradendron, Viscum
(Mistletoes)
• Orobanche (Broomrapes of Tobacco)
• Striga (Witchweeds of Monocots)
Symptoms
• Orange or Yellow Strands Entwine Around
Aboveground Parts of Host Plants
• Patches in Field Enlarge during Growing
Season
• In Perennial Host Crops, Patches Become
Larger Every Year
• Produces Clusters of White, Pink or
Yellowish Flowers in Late Spring, Summer
• Form Seeds
Dodder
• Affects Growth & Yield of Infected Plants
• May Transmit Viruses
• Slender,
Twining Plant
• Leafless (Tiny
Scales in Place
of Leaves)
Disease Development
• Seed Overwinters in Infested Fields or Is
Harvested with Seed of Crop Plants
• Seed Germinates during Growing Season
• Produces Slender Shoot but No Roots
• Shoot Rotates in Search of Host
• If No Contact with Susceptible Plant, Stem
Falls to Ground, Lies Dormant a Few Weeks,
Dies
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• If Contact with Susceptible
Plant, Encircles It & Begins
to Climb
• Sends Haustoria Inside Leaf or
Stem
• Seeks Vascular Tissues where
Absorbs Food & Water
• Base of Dodder Shrivels & Dies
• Loses All Connection with Ground
• Becomes Entirely Dependent on Host for
Nutrition
http://www.science.siu.edu/parasitic-plants/Cuscutaceae/images/Cuscuta.JPEG
Dissemination of Seed
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•
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Animals
Water
Equipment
Contaminated Crop Seed
Control Measures
• Twisting Tips Attack
Adjacent Plants
• Forms Patches of
Infection
• Suppresses Growth of
Infected Plants
http://www.science.siu.edu/parasitic-plants/Cuscutaceae/images/Cusc.haust.JPEG
Effect on Host Plants
• Weakened by
Parasite
• Vigor Declines
• Yields Decrease
• May Be Smothered
or Killed by Dodder
Mistletoe
• Dodder-Free Seed
• Clean Equipment Before Going to Next Field
• Limit Movement of Domestic Animals from
Infested to Clean Fields
• Spray Scattered Patches Early in Season with
Contact Herbicides
• Cut or Burn Patches
• Frequent Tillage or Flaming to Control
Widespread Infection in Field
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Dwarf Mistletoe
• On Conifers
• Monoecious
– Produces Flowers at Age 4-6 Years
– Male Shoots Die After Flowering
• Stunts, Deforms or Kills Hosts including
Height Reduction by 50-80%
– Female Shoots Die After Seeds Discharged
• Fruits
• Reduces Timber Quality
– Mature 5 to 16 Months After Pollination
• Shoots Grow in Tufts along Twigs of Hosts
– Turgid with Considerable Internal Pressure
• Sends Wedge-Shaped Haustoria Inside
• Infected Twigs & Branches Develop
Swellings & Cankers, Sometimes Witches’Brooms
• When Disturbed, Fruit Expels Seed Upward or Outward
at Distances up to 15 Meters
– Seed Covered with Sticky Substance, Adheres to
Surface It Contacts
– Occasionally Birds Transport Seed on Bodies
Disease Development
• Seed Attaches to Bark or Twig of Susceptible
Host
• Germinates & Produces Germ Tube/Radicle
• Grows along Bark Surface Until It Meets Bud
or Leaf Base
• Produces Rootlike Haustorium to Penetrate
Bark, Reach Phloem & Cambium
http://www.science.siu.edu/parasitic-plants/Viscaceae/images/Phor.tom.seed.JPEG
– Absorb Nutrients from Host
– Sinkers that Reach Cambium Embed in Wood as It
Is Laid Down Each Year but Always Retain
Connections with Strands in Phloem
• When Well Established, Buds Are Produced &
Develop Shoots in Subsequent Years
• Center of Infection usually Deteriorates &
Becomes Attacked by Secondary Fungi
• If Witches’-Brooms Are Produced, Haustoria
Invade All Branches & Produce Mistletoe
Shoots Along Host’s Proliferating Branches
• Develops System of Longitudinal Strands &
Radial Sinkers
Effect on Host Plants
• Obtains Water, Nutrients from Host
• Starves & Kills Terminal Portion of Branch
• Saps Vitality
• Upsets Hormonal Balance of Host
– Causes Excessive Cell Enlargement & Division
– Results in Swellings & Deformities on Branches
– Stimulates Excessive Shoot Formation
• Predisposes Trees to Wood-Decay & Root
Pathogens, Beetles, Wind Breakage
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True or Leafy Mistletoe
• Infects Hardwood & Fruit Trees
• Symptoms Similar to Dwarf Mistletoe
• Parasitic Evergreens
– Well-Developed Leaves & Stems
• Usually Small, Dioecious Flowers
• Haustorial Sinkers Grow in Branches & Stems
• Spread by Birds that Eat Berries
– Excrete Sticky Seeds in Tops of Taller Trees
Broomrapes
• Occur in Warm & Dry Regions Worldwide
• Attack 100s of Species of Herbaceous Dicots
• Pathogen Whitish to Yellowish Annual
– Fleshy Stem, Scalelike Leaves
– Numerous Pretty Snapdragonlike Flowers Arising
Singly Along Stem
• Seed Pods about 5 mm Long
– Each Contains 100s of Tiny Seeds
• Develops a Stem that Looks Like Asparagus
• Secondary Roots Spread to Other Host Roots
• End with Clusters of Broomrape Plants Arising
from Soil around Infected Host Plants
• Seeds Germinate
– Produce Radicle, Grow Toward Root of Host,
Attach, Produce Appressorium that Surrounds
Root
Excellent Information On Parasitic
Plants & on Other Mistletoes:
http://www.science.siu.edu/biologicalsciences/biol200/biol200b/Nickrent/DLNlectures/200.Nutrition.html
“…I don't want to leave you with the impression that all
mistletoes are bad! The vast majority of mistletoe genera &
species occur in the tropics. They are actually members of a
different family than our Christmas mistletoe. These "showy"
mistletoes (family Loranthaceae) are spectacular plants, often
with large, brightly-colored flowers [Macrosolen]. These plants
have fascinating coevolutionary relationships with
birds (Dicaeum) that not only pollinate their flowers
but also disperse their seeds…”
• Overwinters as Seeds
– May Survive in Soil 10 Years or Longer
• Germinate when Roots of Certain Plants
Grow Near Them
• Not All Plants Susceptible
• Some Cells Differentiate into Parasite Xylem
Vessel Elements
– Connect Host Xylem with Main Vascular System of
Parasite
• Other Undifferentiated Cells Attach to
Phloem Cells to Obtain Nutrients from Them
Witchweed
• Native to Africa, Asia,
Australia
• Discovered in
Carolinas in 1956
• Quarantines Confined
Parasite to that Area
– Mass of Undifferentiated Cells Arise & Penetrate
Host
– Absorb Nutrients & Water from Xylem
http://www.science.siu.edu/parasitic-plants/Scrophulariaceae/images/Striga.asia2.JPEG
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