Kevin Ong, PhD. Associate Professor and Extension Plant Pathologist Director – Texas Plant Disease Diagnostic Laboratory College Station, TX
Basic Plant Pathology Disease ID and what not.
What is a PLANT DISEASE?
Any alteration of a plant that interferes with its normal appearance, function, or value and renders it unfit for its normal use.
TWO kind of disease
• Infectious – Transmissible from plant to plant – Caused by biotic (pathogenic) agents
• Non-infectious – Disorder caused by unfavorable physical
environmental (physiogenic) effect
What can make plants sick?
Baudoin, A.B.A.M. 2007. The Plant Disease Doughnut, a Simple Graphic to Explain what is Disease and what is a Pathogen. The Plant Health Instructor. DOI: 10.1094/PHI-T-2007-1221-01
Plant Disease Central Concepts
CONCEPT #1: Disease triangle
• Three factors:
PATHOGEN (disease causing agent)
DISEASE
The Disease Triangle
PATHOGEN (disease causing agent)
Susceptibility Susceptibility Susceptibility
Disease Occurs
Disease
CONCEPT #2: Disease Cycle
Overseasoning/ Overwintering
Management
Management
Management
Infection
Host
Reinfection
Management
Management
Glossary – the language
Sign and symptoms Symptomology
SIGN The pathogen (or parts of) can be visually
observed on the host plant.
SYMPTOM External or internal reaction or alteration of a plant due to the
disease
Sign or Symptom?
Urediospores
Teliospores
Symptomology • Anthracnose
– Describes an appearance as dark, sunken leaf, stem, or fruit lesions.
– Typically describe symptoms made by fungi
Ivy- Colletotrichum
Nandina
euonymus
Ash- Gnomoniella
Symptomology
• Blight – Characterized by
general and rapid killing of leaves, flowers, or stems.
Rose-Botrytis
Red cedar -Phomopsis Oleander - Rhizoctonia
Forsythia-Sclerotium
Symptomology • Canker
– A necrotic, often sunken lesion on a stem, branch, or twig of a plant. Sycamore-Discula
Holly
Symptomology
• Chlorosis – Yellowing of
normally green tissue due to chlorophyll destruction or failure of chlorophyll formation
Rose-iron chlorosis
Symptomology • Dieback
– Progressive death of shoots, branches, and roots generally starting at the tip.
Rhododendron-Phytopthtora
Podocarpus-Botryodiplodia
Symptomology • Gall
– A swelling or overgrowth produced on a plant.
– Gall is plant tissue
Rose-Agrobacterium
Azalea-Exobasidium
Pine-Cronartium
Symptomology • Leaf spot
– A self-limiting lesion on a leaf.
Photinia-Entomosporium
Rose-Diplocarpon
Ivy-Xanthomonas
Symptomology • Mildew
– Used to describe fuzzy growth on plants.
– Typically refers to mycelium and spores of fungi that are observed.
Euonymous-Oodium
Crape myrtle-Erysiphe
Rose-Peronospora
Symptomology
• Ringspot – Circular area
of chlorosis with a green center.
Orchid-freeze
INSV
Symptomology
• Rosette – Short, bunchy
habit of plant growth.
Rose rosette (UT-Knoxville)
Rose-unknown
Symptomology
• Scab – A roughen, crust-like
disease area on the surface of a plant organ.
Apricot-Cladosporium
Symptomology
• Scorch – Burning pattern on leaf
margins. – Typically would indicate
water deficiency problems.
Sycamore-Xylella
Oak-Ceratocystis
Symptomology
• Shot-hole – Holes on
leaves.
Cherry laurel-Xanthomonas (UT –Knoxville)
Symptomology
• Stunting – Result of
reduced plant growth.
Cotton-Sting nematode
Symptomology • Wilt
– Loss of rigidity and drooping of plant parts generally caused by insufficient water in the plant.
Azalea-Cylindrocladium
Rose-Verticillium