Agriculture Reference
In-Depth Information
Semi-persistent
: the insect can be acquired after 15-30
minutes of feeding and the ability to transmit is retained
for a few days.
Persistent or circulative
transmission: the insect needs
to feed for up to several hours on an infected plant to
acquire virus, which then needs to circulate through the
insect's body to the salivary glands for transmission
to occur. The insect may retain the ability to transmit
for life.
In some instances, the virus may also replicate or
reproduce in the insect during the circulative transmission
process
(propagative)
.
Nematodes
Nematodes are microscopic, non-segmented roundworms
that belong to the animal kingdom. They occur in almost
every soil and water habitat in the world and most
nematode species feed on bacteria and organic matter.
Nematodes attacking plants have a hollow, spear-like
structure (stylet) near the mouth, used to pierce the wall
of plant cells and ingest cell contents. Feeding often results
in the formation of galls or lesions on roots or distortion
of other plant parts. Nematodes move by swimming in
films of water between soil particles or on plant surfaces.
They spread by water, movement in infested soil and on
contaminated machinery, and in infected planting material.
Fig 1.11 Plant viruses viewed through an electron microscope. There
are many shapes but isometric and flexuous rods are common.
Table 1.3 Some plant viruses in Australia
VIRUS/VIRUS GROUP
MEANS OF SPREAD
IMPORTANT HOST PLANTS
Apple mosaic virus
(Ilarvirus)
Vegetative propagation
Apple
Banana bunchy top virus
(Babuvirus)
Vegetative propagation, aphids (persistent)
Banana
Citrus tristeza virus
(Closterovirus)
Vegetative propagation aphids (semi-persistent)
Citrus species
Cucumber mosaic virus
(Cucumovirus)
Seed, vegetative propagation, aphids
(non-persistent)
Wide host range including banana, legumes,
vegetable, ornamental and weed species
Grapevine fan leaf virus
(Nepovirus)
A plant parasitic nematode
Xiphenema
index
Vitis
species
Mirafiori lettuce big vein virus
Zoospores of soil-borne fungus
Olpidium
brassicae
Lettuce
Lettuce mosaic virus
(Potyvirus)
Lettuce seed, aphids (non-persistent)
Lettuce
Papaya ringspot virus
(Potyvirus)
Aphids (non-persistent)
Papaya (type P) Cucurbits (type W)
Potato leaf roll virus
(Polerovirus)
Aphids (persistent), vegetative propagation
(tubers)
Potato, tomato
Prunus necrotic ringspot virus
(Ilarvirus)
Vegetative propagation, seed, pollen
Prunus
species, e.g. plum, peach, cherry
Squash mosaic virus
(Comovirus)
Seed, several leaf chewing beetles
Cucurbits
Potato virus Y
(Potyvirus)
Aphids (non-persistent)
Potato, tomato, capsicum
Tomato spotted wilt virus
(Tospovirus)
Thrips (persistent, propagative)
Wide host range among vegetable, ornamental
and weed species
Tomato mosaic virus
(Tobamovirus)
Seed, contact by handling, contaminated
implements
Tomato
Tomato, bean, capsicum, several weed species
Tomato yellow leaf curl virus
(Begomovirus)
Silverleaf whitefly (
Bemisia tabaci
) (persistent)
