Common Viruses - British Columbia

APPLES AND PEARS:

Apple Stem Grooving
(causal agent: Apple Stem Grooving Virus)

While the virus does not cause obvious symptoms in commercial cultivars, it induces symptoms in indicator plants and certain size controlling rootstocks. Infected Virginia Crab frequently develops long grooves on the woody stems, which become apparent after the bark is removed. If the grooves are clustered, sunken or flattened areas are visible without removing the bark. Swelling of the scion stem at the union with a sensitive rootstock often occurs. These unions break easily revealing plates of necrotic xylem above the graft. The scion component may eventually die, while the rootstock remains unaffected.

If the union is severely affected, leaves become small, pale green, and drop prematurely.

Summary: Nemeth 1986

Apple Stem Pitting
(causal agent: Apple Stem Pitting Virus)

Commercial varieties show symptoms only if they have been grafted on Virginia Crab, although the virus can cause latent infection in other rootstocks. If infected, the root system weakens and declines, causing the dieback of the scion. Sunken depressions and grooving develop on the stem and the limbs below the union, and longitudinal sutures appear on the bark. In its mild form, symptoms develop only after the second year following inoculation. If severely infected, moderate pitting in the wood occurs during the second year worsening thereafter.

Fruits of Virginia Crab are small and malformed with depressions ('flute fruit' symptoms).

Summary: Nemeth 1986

Apple Chlorotic Leafspot
(causal agent: Apple chlorotic leafspot trichovirus)

Synonyms: Pear ring pattern mosaic

Most commercial apple cultivars do not exhibit symptoms of infection.

Common symptoms in sensitive cultivars can include the following:

1. translucent or chlorotic spots with asymmetrical leaf distortion
2. irregular diffused chlorotic rings and line patterns on leaves of reduced size, which often drop prematurely
3. various degrees of stunting
4. terminal dieback of some clones
5. inner bark necrosis and pitting of the xylem
6. severe local bark necrosis surrounding the inoculum buds grafted on some cultivars
7. tree decline on sensitive rootstocks.

Summary: Fridlund 1989

STONEFRUIT

Prunus Necrotic Ringspot
(causal agent: Prunus necrotic ringspot ilarvirus)

Synonyms: Cherry ringspot, Cherry tatter leaf, Peach ringspot, Peach necrotic leaf spot, Sour cherry necrotic ringspot

Two distinct phases appear. In the acute (shock) phase, bud break is retarded and many buds die before openning. Twigs from the previous year are killed or cankers form at the nodes. Chlorotic or necrotic spots develop on spring leaves. New growth is symptomless,however, except for necrotic spotting. In its chronic phase, the disease masks its symptoms. The vigor of the trees is reduced and their development suppressed. Lateral spurs and leaf buds die, and rough bark symptoms appear. Fruit yield declines and fruit maturity is delayed as cracking and corking develop in the sutures.
Summary: Nemeth 1986

Prune Dwarf
(causal agent: Prune Dwarf Ilarvirus)

Synonyms: Cherry chlorotic ringspot, Fellenberg mosaic, Peach stunt, Plum Dwarf, Plum willows, Prune mosaic, Shoestring of Italian Prune, Sour cherry yellows.

Symptoms vary according to the species/cultivar of the host, virus strain, and temperature. Symptoms are more pronounced at lower temperatures.

General traits include chlorosis, necrosis, leaf distortion, stunting, and gum flow. In sweet cherry and sour cherry trees, symptoms are masked by complex infections with other pathogens.

Summary: Nemeth 1986

Little Cherry Virus
(causal agent: Little Cherry Virus)

Symptoms vary greatly, however cultivars with darkly red fruits tend to be more severely damaged than those that are lighter.

Leaf margins curl slightly upward, followed by a red coloring or bronzing, which is more apparent on the upper surface in interveinal areas; tissues along.

Fruits develop normally at the start of the vegetative period but by harvest their size is one-half to two-thirds that of normal fruit. Affected fruits have a dull red color; are angular shape, having three flat sides tapering towards the end., have diminished flavor, even if other symptoms are not present; and tend to ripen late, if at all.

Summary: Nemeth 1986