Plant Viruses

Question 1

List and describe some of the unique properties of plant viruses

Answer 1

-multple separate virions
-no trues dsDNA
-No true retovireses
-most are +ssRNA
-transmitted by vectors
-lack envelops
-viral replication complexes formed from intracellular membranes

Question 2

What are the ways that plant viruses are transmitted and spread in the field?

Answer 2

1. vegetative propagation materials
2. mechanical transmission throigh minor abrasions
3. vertical transmission
4. biological vectors like mites
5. humans

Question 3

What are the biological vectors that transmit plant viruses? Plant viruses that are transmitted by vectors are divided into four groups. What are these groups? How do you distinguish them?

Answer 3

aphids, leafhoppers, planthoppers, etc
1. non-curculative, non-persistent
-quick, just on the mouth
2. non-circulative, semi-persistent
-quick, mouth and forgut
3. circulative, non-propagative
-the virus circulates inside the insect and can persist for days to weeks
4. circulative, propagative (arboviruses)
-involves the virus being replicated or propagated within the vector

Question 4

Describe the methods that are in use for the diagnosis of plant viruses

Answer 4

1. biological assays (indicator indexing): based on infectivity
2. protien-based:
   -ISEM, ELISA, western blost
3. nucleic acid-based:
   -nucleic acid hybrization, PCR, qPCR, RT-PCR, RT-qPCR, etc

Question 5

Upon entry of a plant virus into its host plant, it goes through three phases of translocation before causing a systemic infection. Discuss each of these processes

Answer 5

1. introcellular movement, cytosyeletion (actin filament), vesicular transport
2. cell-to-cell movement, via plasmodesmata
3. systemic movement, via phloem (vasculature) ; sieve element

Question 6

Describe the two general strategies that plant viruses use to move intercellularly

Answer 6

1. non-tubule-assisted movement
2. tubule-assisted movement

Question 7

Woody perennial crop plants such as grapevine and pome species are often mix-infected with multiple viruses and their strains. Can you think of reasons that are responsible for mixed infections in these plant species?

Question 8

what are the strategies virologists use to eliminate viruses from a vegetatively propagated plant such as fruit crops to produce virus-free stock plants?

Answer 8

-shoot tip tissue culture (meristem)
-heat therapy
-chemotherapy

Question 9

what are viroids?

Answer 9

parasitic RNA even smaller than the smallest virus
-discovery by theodor diener
-highly stable due to extensixe secondary stucture
-dont encode protien

Question 10

acquisition period

Answer 10

the time required by an insect vector to acquire a sufficient amount of virions from the infected plant to allow transmission to another plant

Question 11

latent period

Answer 11

the duration of time between the acquisition of viruses by the vector and its ability to transmit the virus to a new plant

Question 12

retention period

Answer 12

the time period in which the insect vector continues to infect new plants after a sign acquisition event.

Question 13

how to prevent spread?

Answer 13

-control insect vectors but they may develop resistance
-breeding for virus-resistant cultivars, rare natural resistance gene
-cross protection, prior infection of a virus provides protection against closely related more pathogenic ones
-certified virus-free propagation stocks (shoot tipp, chemo, heat)
-genetic engineering