APPLE AND PEAR - Diseases of Fruit Crops in Australia - page 46

Australia remains free from several viruses, viroids and
phytoplasmas that cause serious problems in apples in
many other countries. All apple material introduced into
Australia is subject to post-entry quarantine to assess its
health status.

•

STONY PIT

■ Cause
Pear stony pit virus.

Symptoms
Normal fruit development is affected, and fruit become
pitted and deformed. Tissue at the base of the pits becomes
very hard and heavily pitted fruit become so gnarled and
woody that they are very difficult to cut. Severely affected
fruit are unmarketable. Symptom severity and the
number of fruit affected vary from season to season.
Some trees show symptoms on only one branch or one
side of the tree.

Fig 3.38 Apple mosaic virus symptoms on terminal growth.

Positive detection and identification is by biological
testing using sensitive indicator varieties combined with
laboratory tests.
Some exceptions are apple mosaic virus and apple green
crinkle virus . The former produces conspicuous pale to
bright cream coloured areas on leaves as they expand in
spring. Fruit produced on trees infected by green crinkle
virus are small and malformed, sometimes with russetted
areas in the skin depressions.

Source of infection and spread
The virus spreads by vegetative propagation (i.e. budding,
grafting and rooting cuttings). Little, if any, spread occurs
within an orchard. Stony pit virus is not transmitted in
pear seed and nor is it spread by insects. Pear is the only
known host.

Source of infection and spread
Viruses infecting apple trees in Australia are spread almost
exclusively by infected propagation material (e.g. infected
rootstocks and budwood).
Once infected, plants stay infected for life, even though
symptoms may be absent or transient.

Importance
Stony pit is a serious disease because fruit from affected
trees is unmarketable. Stony pit virus is one of several
viruses and viroids found in Australian pear varieties.
All are controlled by using virus-tested propagation
material.

Importance
Virus infection is a major cause of yield decline and poor
growth of trees.

Management
•

Use virus-tested propagation material in nurseries and
when topworking trees.

Fig 3.40 Stony pit internal and external symptoms showing browning
and pitting.

Fig 3.39 Apple ringspot virus symptoms.