Wilts Flashcards
What are the two main disease assessments?
- Qualitative
2. Quantitative
What is a qualitative assessment?
Give an example…
Incidence data, easiest to perform, yes and no questions.
Most useful when disease is uniform or any disease is detrimental, however it is statistically limited.
What is a quantitative assessment?
Give an example…
More difficult, more important what disease is not uniform.
Visual acuity is a problem, ability to distinguish differences.
What is visual acuity?
Percent of leaf area…
More repeatable and more reflective of visual abilities.
Non linear scale
Normalizes variance instabilities
Single disease assessment…
example
An assessment with an endpoint, for example, harvest data, sugar boots to assess roots.
Multiple Assessments….
example
- Area Under Disease Progress Curve(AUDPC)
- Models
- Generalized Variance Models
Qualitative- single assessment example
Fruit and cosmetic diseases marketable at the end of harvest
Qualitative- multiple assessment example
Rate of infection of wilt disease in an orchard.
Quantitative- single assessment example
When the assessment is destructive, for example assessing root rot damage for sugar beet plants.
Quantitative- multiple assessment example
Leaf spot, the amount of leaf tissue lost over time so assess photosynthesis.
List 3 main wilt diseases discussed in lecture…
- Fusarium oxysporum f. sp.
- Verticillium dahliae and V. albo-atrum
- Cephalosporium gramineum
5 main wilt symptoms
- Vascular necrosis (systemic)
- Epinasty (downturning of leaves)
- Sectoring necrosis (portion of section dies)
- Foliar asymmetry (leaf turn)
- Death
Infection process for Fusarium Oxysporum?
- Similar to root rot, goes in to the vascular elements of the plant.
- No longer moving by hyphae, and produces microconidia and moves through water in the plant.
- Live cells try to help regulate vascular system to fight off infection by producing Tyloses
What causes wilting?
Conidia, mycelium, toxins, gums and tyloses restrict water movement. After wilt the pathogen invades other tissues and starts to sporulate and produce chlamydospores (asex. surv. spores) for overwintering.
Fusarium oxysporum f. sp.
characteristics…
Systemic
Highly specialized (limited host range)
***Warm weather pathogen (southern states and house plants)
Fusarium oxysporum management
- Prevention
- Resistance
- Rotation
- Cool soils, plant no till…
Verticillium wilt
characteristics…
Systemic
Generalist
Enhanced by wounding of roots (nematodes increase path.)
Uses phialid-like spores for movement within vascular tissues.
***Cool weather pathogen
List two verticillium species
V. albo-atrum - (Overwinters as microsclerotia (little packets of mycelium for survival)
V. dahliae - (Overwinters as dark thickened strands of mycelium looks black)
Verticillium wilt management
- Prevention
- Resistance
- Fallow (mint)
- Black mulch (to increase soil temperatures)
Cephalosporium Stripe
Necrosis of central vein of wheat
* cool weather pathogen*
Cephalosporium Stripe species…
Cephalosporium gramineum
Only attacks winter wheat
* Frost (Freezing and thawing helps pathogen) Fungus enters through the roots by damaged winter having of soil*
Controls Cephalosporium gramineum…
- Rotate to spring wheat (or dicots) for 2 cropping cycles or more
- Tillage
- Plant late
- Adjust pH above 5.5 re
note… wireworms increase insidence
What is a monocyclic disease? Give an example…
Completes one disease cycle in a given season.
- ex… Fusarium
What is a polycyclic disease? Give an example…
Completes multiple disease cycles within a given season.
- ex… Pythium (secondary inoculum with zoospores and hyphae)
What is an epidemic?
A rapid increase in disease often characterized by multiple disease cycles being completed within the typical lifespan of the host organism.
Characteristics of Dutch Elm Disease
- Exotic disease presumably from Asia introduce in 1930s
- Wiped out American elm (77 million trees)
- Flagging and moves to neighboring trees
- Vascular necrosis
What vectors cause Dutch Elm Disease?
- European and American Elm Bark Beetle
2. Banded Elm Bark Beetle.
Steps of disease infection of Dutch Elm
- Females lay eggs in weak trees
- Larva then pupate, become adults and leave the plant
- Fungus sporulates in galleries
* Ophiostoma ulmi******* - Beetles covered in spores feed on healthy elm and deposit spores on wounded tissue
Controls for Dutch Elm Disease
- Inject fungicides- $$$$
- Rogueing, cut tree down or take off bark.
- Dutch elm disease recovery, resistance.
New fungus to ruin Elm trees?
O. novo- ulmi
Pine Beetle Attack!
- Pines and Spruce trees lost 3.9 million nation wide.
- 2008 in Montana lost 200
Mountain Pine Beetle (associated fungus)
Ophiostoma and Ceratocystis species
* Ophiostoma polonicum*
Makes bubble gum marks on the outside of the plant, and causes blue staining.
