Plant Virology

Question 1

Local lesions

Answer 1

A localised area of diseased tissue (chlorotic or necrotic)

Question 2

Chlorosis

Answer 2

Yellowing of leaves

Question 3

Mosaics

Answer 3

Yellow leaves on a green background

Question 4

Necrosis

Answer 4

Tissue death - either by stress or via specific plant-virus interactions

Question 5

Morphogenetic disturbances

Answer 5

Growth reduction, colour deviations, wilting, malformation of specific organs, premature leaf drop or curling

Question 6

Whiteflies

Answer 6

Transmit about 70 serious disease agents - cassava mosaic virus

Question 7

Aphids

Answer 7

65% of viruses with invertebrate vectors are transferred

Question 8

Nematodes

Answer 8

Several wide spread viruses are transmitted via nematodes through soil feeding on root epidermal cells

Viruses can survive within a nematode for up to a year

Question 9

Fungal vectors

Answer 9

wheat mosaic virus carried in the resting spores of fungus - plasmodiophoromycete

Virus can survive for many years

Tobacco necrosis virus - carried on surface of spores - only survive a few hours

Question 10

Rhizomania

Answer 10

Disease of sugar beet caused by virus

Beet necrotic yellow vein virus (BNYVV)

Extensive proliferation of lateral roots - also necrosis of vascular bundles and severe stunting of plants

Question 11

Mechanical transmission

Answer 11

Introduction of virus or viral RNA into a wound made through the plant surface

tobacco mosaic virus (TMV) and potato virus X (PVX) - very succesful viruses - no insect vector

Question 12

Sexual transmission

Answer 12

1/5 of plant viruses are transmitted through seed of infected host

Persist in seed for long periods of time

Seed can become infected via a number of routes including sexual transmission via pollen

Question 13

TMV

Answer 13

First virus to be shown to consist of RNA and protein

First virus to be characterised by X-ray crystallography

First virus to be used for electron microscopy

Replication - once it enters cell through wound site - the virus particles disassemble to expose viral RNA - acts as mRNA immediately to produce the replicase protein

Replicase proteins associate with 3’ end of the +ve sense viral RNA for the production of -ve sense RNA

-ve sense RNA acts as template to produce both full-length genomic +ve sense TNa as well as the +ve sense subgenomic RNAs

Question 14

Cross protection

Answer 14

Mild strains of viruses inoculated onto plants prevent more virulent strains from infecting the plant

Risks include viruses mutating and virus may no longer be mild