Viral Plant Diseases Flashcards
How are viruses proven to exist?
Sap from infected plant forced through bacterial proof filter… filtered sap used to recreate disease
Virus names
First host on which it was found (not all hosts are infected)
Symptom
- ex Cucumber mosaic virus, tomato spotted wilt virus, etc…
Isolate
Collected from a particular place
Strain
Isolate with some kind of difference from previous others
Shapes of viruses
- Rod
- Bacilliform (bullet-like)
- Flexous rod
- Polyhedral (crystal-like)
- Bipartite … gemini = 2 pieces
Viruses are ‘obligate parasites’ because…
- Need host materials
- Can’t reproduce on their own
- Not considered living… more like infectious chemicals
Three steps of infection
- Initial infection
- Cell to cell until particles move to phloem
- Moves through plant
- depends on non-lethal wound sites or vector transmission *
Movement through plants
Source to sink with photosynthesis
Results in systemic infection
General symptoms
- Stunting
- Lesions … necrotic spots, local
- Mosaics … blotches
- Yellowing … associated with stunting
- Distortion … curling of parts / leaves … “shoestringing”
Physiological effects
- decreased photosynthesis
- increased respiration
- N2 decreases
- translocation decreases
Survival of viruses
Some are ‘stable’ and can stay viable for days.
Most are unstable and cannot survive outside of a host… vectors are very important
Spread of viruses
- Seed … infected cells.
- Grafts … color streaking, variegation (desirable)
- Dodder … parasitic plant on plants
- Nematodes
- Pollen … with systemic infection
- Mechanical … people
- Insects ***
Important insect vectors
- Aphids
- Leafhoppers
- Sharpshooters
- Whiteflies
Two types of insect transmission
Non-persistent = most common by plants
Persistent = mostly by leaf hoppers
Non-persistent transmission
- Most common by plants
- Tend to cause mosaics
- Fast transmission
- Short retention time < 6 hours
- No latent period
Persistent transmission
Most common by leafhoppers
Circulative - virus survives in hemolymph, does not replicate
Propagative - virus multiplies in insect, associated with all stages of life. Retention time measured in weeks… latent period - virus circulates through insect
Virus ID
- Host range
- means of transmission
- Temperature of inactivation
- Indexing - grafting of affected plant onto indicator plant
- Serology - ELISA, PCR
Virus Management
- Resistance… little or no input by grower. Fully susceptible plants that can yield well despite infection
- Resistance to VECTOR … undesirable traits
- Cultural practices … Delay infection! Time of planting, avoid insect migration. Mulches = reflective, insects don’t recognize site. Certified seed
- Chemical … none for virus themselves
- Biocontrol … Predator of vector, activate plant defenses
- Transgenic Resistance … GMO
Plant Viruses in AL
- Cucumber Mosaic Virus
- Tomato Spotted Wilt Virus
- Papaya ringspot
- Watermelon Mosaic Virus
- Zucchini Yellow Mosaic
- Potato Leaf Roll
Plant Viruses of AL field crops
Wheat
- Barley yellow dwarf (aphid)
- Cereal yellow dwarf (aphid)
Peanut
- TSW
- Peanut stunt
Cucumber Mosaic Virus geo
worldwide
Cucumber Mosaic Virus hosts
very wide range, more than any other plant virus
- ex. tomato, beans, beets, petunias, lilies
Cucumber Mosaic Virus symptoms
Young leaves become mosaic and mottled… possibly distorted and wrinkled.
Subsequent growth reduced, shortened internodes… fewer flowers / fruits
Cucumber Mosaic Virus signs
NONE
Cucumber Mosaic Virus disease cycle
- OW in perennials
- aphids - non-persistent
- few plants initially
- man can transmit this further
- systemic in plants
- OW
Cucumber Mosaic Virus managament
- Resistance
- Eliminate weed hosts and manage insect vectors… promote beneficials
- Certified seed
- Prevent insects from reaching crop (netting)
- Remove / burn diseased plants
Tomato Spotted Wilt Virus host
wide range -> tomato, peanut, annual crops
Tomato Spotted Wilt Virus geo
limited, (present where tested)
Tomato Spotted Wilt Virus symptoms
- Chlorotic, concentric rings
- Mottling of leaves
- Bud necrosis
- Stunting in early plants
- Less severe in older plants
Tomato Spotted Wilt Virus signs
NONE!
Tomato Spotted Wilt Virus disease cycle
- thrips vector … larvae can acquire virus and transmit it for lifetime
- no seed transmission
Tomato Spotted Wilt Virus losses
reduced production, smaller plants
Tomato Spotted Wilt Virus management
- resistance
- delayed planting
- higher populations help minimize yield reduction
- alternate insecticides
- conventional tillage helps
Prunus Necrotic Ringspot host
fairly limited to Prunus = stonefruits.
- cherry, plum, peach, nectarine, almonds
- some ornamantals … rose
Prunus Necrotic Ringspot geo
worldwide, wherever hosts are grown
Prunus Necrotic Ringspot symptoms
- delayed foliation in spring, may be localized or systemic
- later, foliage with light and dark green ringspot… spots are necrotic, fall off leaving shothole damage
- blossoms can be distorted, limited fruit set
- overall reduction in plant growth and vigor
Prunus Necrotic Ringspot signs
NONE!
Prunus Necrotic Ringspot disease cycle
- OW in infected trees
- spread by pollen (more rapid in older orchards)
- virus infects through flower
Prunus Necrotic Ringspot management
- virus free stock
- rogue (remove affected plants)
- remove affected wild hosts
- avoid planting too close
