Agriculture Reference
In-Depth Information
3
APPLE AND PEAR
domestica
)
Pear
(
Pyrus communis
)
Apple
(
Malus
×
Apples and pears are major fruit crops in all temperate
regions worldwide. Pome fruit (apples, pears and nashi)
production is one of the largest fruit industries
in Australia.
Source of infection and spread
The bacterium has a wide host range and survives as an
epiphyte on many plant species. It commonly overwinters
in buds and leaf scars of trees. Populations of the bacteria
increase in early spring to allow further epiphytic
colonisation of leaves and blossoms. The bacteria disperse
in water splash and on insects. The bacteria enter plants
through small wounds and natural openings in the f lowers
and leaves. Symptoms develop when cold, wet weather
occurs during f lowering or in plants affected by late frosts.
Production is concentrated in temperate regions where
winter temperatures allow adequate winter chilling and
summer temperatures are not extreme.
The major apple production areas in Australia are the
Goulburn Valley in Victoria, the Huon Valley in Tasmania,
the temperate highlands and slopes of the New South Wales
central west, the Granite Belt in Queensland, and the wet
temperate coasts of South Australia and Western Australia.
More than 90% of the Australian pear crop is produced
in the Goulburn Valley in Victoria.
Importance
The disease can cause severe blossom loss in pear if
prolonged wet, cold weather occurs during spring.
Apples and pears are propagated vegetatively by budding
varieties onto clonal or seedling rootstocks.
Low-intensity culture has been replaced by high-yielding
varieties grown on dwarfing or semi-dwarfing rootstocks
using reduced plant spacing.
Black spot is an important disease in both crops while
bacterial blossom blight can be serious in pears during
wet spring weather.
BACTERIA
BACTERIAL BLOSSOM BLIGHT
(BLAST) OF PEAR
Cause
The bacterium
Pseudomonas syringae
pv .
syringae
.
Symptoms
Flowers are attacked causing blackening and dieback of
the blossom truss. Black spots develop at the calyx end
of young fruit and may spread until the whole fruit and
stalk are affected. Fruit drop may occur. Infected fruits
and bearing spurs die and branch dieback may occur.
Fig 3.1 Bacterial blossom blight causes dieback and death in
blossoms and spurs. Inset: blossom death.
