Articles
OUTBREAK OF FIRE BLIGHT THREATENING THE LOQUAT INDUSTRY IN ISRAEL
In 1987 Erwinia amylovora was isolated by D. Zutra from a loquat (Eriobotryae japonica Lindle) tree adjacent to a heavily infected pear orchard at Revivim.
A severe outbreak of fire blight occurred on loquat trees during the autumn of 1994.
Loquat is a sub-tropical evergreen tree from the Rosaceae family.
In Israel it is grown intensively on about 350 hectares which yield about 4000 tons of fruit.
Most of the loquat groves are found in open fields.
Some are grown under netting in order to provide protection against birds, bats, hail, winds and to prevent direct sunlight.
A very small portion of the total area is grown in greenhouses, which enable the growers to harvest high quality fruit early in spring.
The flowering stage in loquat continues for a number of months in autumn, varying according to cultivars.
Thinning, first the flowers and later the fruits, creates a wound through which the bacteria can penetrate the plant.
The fruit ripens towards the end of winter and during spring when there are often extremely hot days.
Overhead sprinklers are used over the whole canopy in order to cool the fruit.
This may create a microclimate favouring disease infection.
Vegetative pruning and wounds which are caused during fruit picking may serve as sites for penetration of the bacteria.
The autumn of 1994 was unusually wet and during November-December more than 20 rainy days were recorded.
These rains accompanied by temperature over 18°C might have been the reason for the severe attack of the disease.
Loquat is a very popular fruit in Israel and it can be found growing in many private gardens.
The outbreak of fire blight has affected these trees too and made them a potential and uncontrollable source of infection for the commercial groves.
In loquat the disease causes wilting of the flowers, shrivelling and dehydration of the fruitlet and damages the fruit at different stages of growth.
The infection of the fruit is accompanied by infection of closely attached branches and spreads further to thicker and distant branches.
Infection has been found in off-shoots, which in turn causes direct infection of the trunk.
In the first stages of infection it is not possible to define clear boundaries between the infected and the healthy parts, even though it is possible to see the renewal of growth under the infected area.
In young trees the infection spreads very fast and it may cause complete destruction of the tree.
In adult trees, even though there may be a large number of infected sites, spread of the disease is slower and the tree, being an evergreen, has the ability to renew itself.
The loquat groves which are the most affected by fire blight are those growing in open fields.
Under nets the infection is less extensive and tends to be concentrated on the margin of the grove.
The trees in greenhouses are more protected from external infection.
However, once infection occurs, it develops rapidly due to accelerated vegetative growth, humidity and high temperatures.