Plant Virology Flashcards
Local lesions
A localised area of diseased tissue (chlorotic or necrotic)
Chlorosis
Yellowing of leaves
Mosaics
Yellow leaves on a green background
Necrosis
Tissue death - either by stress or via specific plant-virus interactions
Morphogenetic disturbances
Growth reduction, colour deviations, wilting, malformation of specific organs, premature leaf drop or curling
Whiteflies
Transmit about 70 serious disease agents - cassava mosaic virus
Aphids
65% of viruses with invertebrate vectors are transferred
Nematodes
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
Fungal vectors
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
Rhizomania
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
Mechanical transmission
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
Sexual transmission
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
TMV
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
Cross protection
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