Bergamot

Citrus bergamia

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Description

Bergamot, Citrus bergamia, is an evergreen tree grown for its fruit, flowers and leaves which are used primarily for the extraction of its lemon scented oil. Bergamot is an erect branching tree with oval leaves which are alternately arranged. The tree produced clusters of white flowers and a fruit that resembles a pear-shaped orange. The fruit is green and turns to yellow when ripe. Bergamot trees can reach up to 4 m (13.1 ft) in height and will remain productive for up to 60 years if managed well. Bergamot may also be referred to as bergamot orange or sour orange and its origin is unknown although it is almost exclusively grown in the coastal plains of Southern Italy.

Uses

The oil produced by the flowers, leaves and rind of the fruit is used in eau de toilette, cologne and soap. The bitter fruit is used to make marmalade and to flavor liqueurs.

Propagation


Basic requirements
Bergamot oranges grow best in regions with a pronounced change in season. They will grow best at temperatures between 12.8 and 37.8°C (55–100°F) during the growing season and 1.7 to 10°C (35–50°F) during dormancy. Mature trees can survive short periods of freezing, whereas young trees will be killed. Trees should be protected from frosts and freezing conditions to prevent damage. The trees will also tolerate drought conditions but perform poorly in water-logged soil. Trees will grow best when planted in a well-draining sandy loam with a pH between 6.0 and 7.5. Soil must be deep enough to permit adequate root development. Trees require full sun and should be protected from wind which can cause damage to the trees.

Propagation
Bergamot seedlings are usually produced by grafting or budding to an appropriate rootstock as seeds will not produce fruit true to type. Grafting is the process by which a scion from one plant is joined to the rootstock of another to produce a new tree. Budding is a special type of grafting where the scion that is joined to the rootstock consists of a single bud. Budding is commonly used in citrus propagation as it is the easier of the two processes and works very well.

Budding
Budding should be carried out when seedling stems have reached roughly the diameter of a pencil (6–9 mm/0.25–0.36 in) and at a time when the bark of the rootstock tree is slipping (this is the term used to describe a period of active growth when the bark can be easily peeled from the plant). Twigs (budwood) should be collected from the previous growth flush or the current flush so long as the twig has begun to harden. The twigs should have well developed buds and should be as close as possible to the diameter of the rootstock onto which it will be joined. It is extremely important to only collect budwood from disease-free trees. The use of diseased budwood can cause the spread of many serious citrus diseases which can kill trees. The budwood to be used for propagation should be trimmed to create budsticks which are 20–25 cm (8–10 in) by removing any unwanted wood and leaves. These budsticks can be stored for 2–3 months under the correct conditions but it is best to use them as soon as possible after cutting.

The simplest way to join the budwood the the rootstock is by T-budding. The area to be joined should be pruned to remove any thorns or twigs and the cut made approximately 15 cm (6 in) from the ground. Using a sharp knife, a 2.5–3.8 cm (1–1.5 in) vertical cut should be made in the stem of the rootstock, through the bark. A horizontal cut should be made at either the top or the bottom of the vertical cut to produce a “T-shape” The horizontal cut should be made a slightly upward-pointing angle and should reach through the bark. Remove a bud from a budstick by slicing a thin, shield-shaped piece of bark and wood from the stem, beginning about 1.25 cm (0.5 in) above the bud. This piece should measure 1.9–2.5 cm(0.75–1.0 in) in length. Immedietely insert the piece of bud into the cut on the rootstock by sliding it under the opened bark so that the cut surface lies flat against the wood of the rootstock plant. Finish the join by wrapping the bud with budding tape.

When the union is made and the tape is removed, the bud is forced to grow by cutting the rootstock stem above the join about 2/3 of the way through the stem. This cut should be made 2.5–3.9 cm (1.0–1.5 in) on the same side as the join. The top of the seedling should then be pushed over towards the ground. This process, known as “lopping” allows all of the nutrients to be diverted to the bud Once the bud begins to grow and reaches several inches in lengthe, the lop can be removed completely from the seedling.

Planting seedlings
Bergamot trees can be purchased as seedlings which have already been grafted and only require planting in the garden or orchard. The best time to plant citrus trees is in Spring after all danger of frost has passed in your area. Standard sized trees should be spaced 3.7–7.6 m (12–25 ft) apart in an area that receives full sunlight, but is protected from strong winds which can damage the trees. Planting against a south facing wall will help protect the tree in cooler climates.

General care and maintenance
Newly planted trees require proper irrigation to ensure they become established. During the first year, water should be applied at the base of the trunk so that the root ball is kept moist to allow the roots to establish in the soil. Newly planted trees should be provided with water every 3–7 days. The soil should be moist, but not wet. Trees planted in sandy soils will require water more frequently. Young trees will also require a light application of fertilizer every month in the first year.

Diseases

Alternaria brown spot Fungi Alternaria spp.

Symptoms

Infected fruit change color prematurely; brown or black lesions on young twigs, leaves and fruit; diseased fruit may fall from tree.

Comments

Avoid overhead irrigation and excessive application of nitrogen.

Management

Plants that are stressed are more susceptible to the disease, ensure plants are provided with water and fertilizer; delaying harvest until diseased fruit has dropped from tree can reduce the number of fruit lost to the disease post harvest; preharvest treatment with fungicide is often ineffective.

Black spot Fungus Guignardia citricarpa

Symptoms

Small brown or black spot and speckles on rinds of fruit; premature fruit drop; reduced fruit yield; symptoms are often more apparent on the side of trees which receive most sunlight; infected leaves generally show no symptoms.

Comments

Widespread in areas of the Southern hemisphere with summer rainfall; fungus survives in decomposing leaves on/in soil around infected trees; spores can be spread by wind and water splash.

Management

Remove leaf litter from around trees to reduce inoculum; keep trees well irrigated during dry periods to reduce leaf fall; apply copper containing fungicides where appropriate.

Canker Bacterium Xanthomonas axonopodis

Symptoms

Slightly raised blisters on leaves with surrounding tissue turning yellow; lesion turn tan brown in color and develop a water soaked margin with white halo; centers of lesions become raised and develop a corky texture; lesions on stems and twigs are raised, corky and dark brown to black in clor with an oily or water soaked margin; raised blister-like lesions develop on fruit; fruit lesions turn dark brown or black and are sunken; fruit drops from tree prematurely.

Comments

Serious disease in humid tropical and subtropical areas; disease spreads rapidly over short distances.

Management

Control of the disease is reliant on timely sprays of copper containing fungicides and the provision of windbreaks to reduce spread of inoculum from infected trees.

Powdery mildew Fungus Oidium tingitaninium
Oidium citri

Symptoms

White powdery patches on upper surface of young leaves and possibly stems and young fruit; newly emerging leaves and shoots may be discolored; severe infestation can cause leaves to drop from plant, twigs to die back and premature dropping of fruit.

Comments

Emergence of disease is favored by cool, damp weather conditions; very common in Asian countries.

Management

Disease can be controlled by timely applications of fungicide to protect new growth flushes; systemic fungicides give longer periods of protection.

Pseudocercospora leaf and fruit spot Fungus Pseudocercospora angolensis

Symptoms

Lesions with gray centers and chlorotic halos on leaves; holes in leaves where lesions have dropped out; lesions may coalesce to produce chlorotic patches on leaves; raised tumor-like growths on young fruit; circular or irregularly shaped flat lesions on mature fruit.

Comments

Can be devastating to citrus trees.

Management

Control relies on the use of copper fungicides.

References

CABI Crop Protection Compendium. (2008). Citrus bergamaia datasheet. Available at: http://www.cabi.org/cpc/datasheet/13437. [Accessed 06 November 14]. Paid subscription required.

Orwa, C., Muta, A,, Kindt, R., Jamnads, R. & Simons, A. (2009). Agroforestree Database: a tree reference and selection guide. Citus bergamia. Available at: http://www.worldagroforestry.org/tree.... [Accessed 06 November 14]. Free to access.

Timmer, L. W., Garnsey, S. M. & Graham, J. H. (2000). Compendium of Citrus Diseases. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopap.... Available for purchase from APS Press.