1506

2: Edible fruits and nuts

Fortunella Swingle

Journ. Wash. Acad. Sci. 5: 167 (1915).

RUTACEAE

x = 7; Fortunella hindsii is a tetraploid.

Major species and synonyms
— Fortunella hindsii (Champ.) Swingle, Journ. Wash. Acad. Sci. 5: 175 (1915). Synonyms: Sclerostylis hindsii Champ. ex Benth. (1851), Atalantia hindsii (Champ.) Oliver ex Benth. (1861).
— Fortunella japonica (Thunb.) Swingle, Journ. Wash. Acad. Sci. 5: 171 (1915). Synonyms: Citrus japonica Thunb. (1780), Citrus inermis Roxb. (1832).
— Fortunella margarita (Lour.) Swingle, Journ. Wash. Acad. Sci. 5: 170 (1915). Synonym: Citrus margarita Lour. (1790).

General: kumquat, kinkan (En).
— Fortunella hindsii: Hong Kong wild kumquat (En).
— Fortunella japonica: round kumquat, marumi kumquat (En). South-East Asia: kin, kin kuit, kuit xu. Thailand: kam kat, som cheet. Vietnam: quat, kim quat, tac.
— Fortunella margarita: oval kumquat, nagami kumquat (En). South-East Asia: chu tsu, chantu.

Fortunella margarita — the most important species by far — and Fortunella japonica are natives of southern China. At present they are only known in cultivation, mainly in China, Japan and Taiwan. Fortunella hindsii is a native of Hong Kong and China, cultivated in China and Japan for the fruits (or collected from the wild in China). Elsewhere it is only cultivated as a very thorny ornamental potplant. Outside the regions of origin, kumquats are mainly grown in the United States for ornamental purposes. On a small scale, kumquats can be found in all subtropical regions.

Kumquat fruits are eaten fresh, prepared e.g. in chutneys, marmalades, jellies or preserved in syrup or candied. Preserved fruits are popular in Penang and Singapore. The thin skin is also edible (a generic character). The plants are popular ornamentals in the United States, often cultivated in home gardens and hedges for their dense green foliage and bright golden fruits. Fruits and leaves are also used for decoration. In Australia a liqueur is prepared from the fruits. In Vietnam the fruits are used in traditional medicine against coughs; around Vietnamese New Year, potted kumquat plants in fruit decorate every home.

No statistical data are available. The use of kumquat fruits as decoration in the gift package industry is said to be important in Florida (United States). In the western world the fresh fruit was sold at about US$ 0.80 per 100 g in the late 1980s.

Kumquat fruits are rich in pectin and vitamin C. Pectin content is highest in the inner peel, reaching 10% of fresh weight a little after ripening; pectin content of the pulp is about half of that of the peel. Vitamin C content of the fruit is highest in the rind, but leaves are a better source than the fruits.
Fortunella japonica contains per 100 g edible portion (rind included): water 89 g, protein 0.9 g, carbohydrates 5.5 g, cellulose 4.1 g, ash 0.5 g. The energy value averages 290 kJ/100 g.

Evergreen shrubs or small trees, usually 2—4 m tall, branches angular when young, rounded when older, sometimes with single axillary spines. Leaves simple, alternate, lanceolate, 3—10 cm long, pointed or rounded at apex, finely toothed from the apex to the middle, dark green, densely glandular-dotted, especially on the underside; petioles often narrowly winged. Flowers borne singly or in few-flowered clusters in axils of leaves, hermaphrodite, 5-merous, small, white, sweet scented; stamens 16 or 20(—24), cohering irregularly in bundles; stigma cavernous within because of large deep-seated oil glands. Fruit an ovoid or globose berry, 1—4.5 cm diameter, 3—7-segmented, peel rather thick, fleshy, aromatic, bright orange or golden yellow. Seeds ovoid, germination hypogeal. First foliage leaves broadly ovate, opposite.
Fortunella hindsii: fruits subglobose, 1—2 cm diameter, with 3—4 segments, brilliant scarlet-orange when fully ripe; leaves ovate-elliptical, tapering sharply at both ends.
Fortunella japonica: fruits globose, 2—3 cm diameter, with 4—7 segments; style caducous; leaves up to 7 cm long, blunt at tip.
Fortunella margarita: fruits ovoid or oblong, 2.5—4.5 cm x 2—3 cm, with 4—5 segments; style persistent; leaves up to 10 cm long, pointed at tip.
Growth occurs only at relatively high temperatures. Trees normally come into bloom much later than Citrus species and enter the condition of induced dormancy earlier. Consequently, trees remain inactive and semi-dormant in subtropical and warm temperate climates during autumn, winter and spring and exhibit growth only during the comparatively short summer season. In the United States first blooms of early spring remain sterile. Fertile flowers appear in summer in axils of leaves on shoots developed in spring. Ripe fruits are harvested from October to January. In Vietnam flowering is in February—March and in June—August. Main harvest is in January—February, second harvest in May—June. In northern India flowering is in March—April and in September—October.
Fortunella polyandra (Ridley) Tanaka (synonym: Citrus swinglei Burkill), the Malayan kumquat or 'limau pagar', is a native of Peninsular Malaysia and Hainan and cultivated as a hedge or wayside shrub in Peninsular Malaysia only, where the desiccated fruit is sometimes sold as a specialty.
Many hybrids of Fortunella exist, both intrageneric and intergeneric. Intrageneric hybrids are: a) the 'Meiwa' kumquat, possibly a hybrid between the oval and the round kumquat, with broadly oval fruits. Sometimes it is considered as a species (Fortunella crassifolia Swingle). It is widely grown in Chekiang Province of China and called 'chintan'; b) the 'Changshou' kumquat, possibly a hybrid between two Fortunella species, a dwarf form, commonly known as potted plant in China. Sometimes it is considered as a species (Fortunella obovata Tanaka). Bigeneric hybrids of Fortunella with Citrus and Poncirus are: limequats, orangequats, citrumquats, procimequats and calamondins. Calamondins are widely cultivated in the Philippines. Formerly they were named Citrus mitis Blanco, Citrus microcarpa Bunge or Citrus madurensis Lour. See the article on x Citrofortunella microcarpa (Bunge) Wijnands. Trigeneric hybrids of Fortunella are: citrangequats, citrangedins and faustrimedins.

Most kumquat species need a cool subtropical or warm temperate climate, with 1100—1500 mm rainfall in the growing season and relatively high temperatures (26—37°C) for optimal growth. They do not tolerate drought or flooding. In the cool periods of the year they enter a condition of dormancy, with a high resistance to winter cold (frosts up to —15°C) even if alternated with milder periods. Fortunella japonica is more cold-tolerant than Fortunella margarita.

Kumquats are rarely grown from seed as seed is difficult to obtain and moreover, seedlings often do not grow well. Shield budding on Poncirus trifoliata Raf. is the preferred method of propagation. Sometimes sour orange and grapefruit are used as rootstocks. Propagation by airlayering is also possible.
In orchards trees are planted 3—4 m x 3—4 m, or, if planted in rows as hedges, with 1—2 m between the plants and 4—5 m between the rows. In Vietnam Eryngium foetidum L., amaranth or kangkong is sometimes planted as a ground cover.
Kumquat plantations need the same tillage and fertilizing as is required for Citrus; fruit size improves up to high nutrient levels. Fertilizers should be applied in late winter to produce a strong spring flush. In winter the previous season's growth should be pruned hard. Some pruning already occurs at harvest, since bearing twigs are usually cut, but additional pruning well in advance of the resumption of growth is beneficial both to fruit size and quantity, especially if the crop has been light.
The following diseases have been observed in kumquat: scab (Sphaceloma fawcetti), green scurf (Cephaleuros virescens), greasy spot (Cercospora citri-grisea), anthracnose (Colletotrichum gloeosporioides), fruit rot (Diaporthe citri) and stem-end rot (Physalospora rhodina).
Kumquats can be attacked by most of the common Citrus pests such as leaf miners, caterpillars and tree borers. They are resistant or immune to Citrus canker. Potted kumquats are subject to mealy bug infestations.
On the American market fresh fruits are usually sold attached to a twig with 2—3 leaves. For decoration, larger branches with several fruits are used.
The keeping quality is good. The firm peel enables kumquat to stand transport very well. Fruit can be stored at 15°C with 85—95% relative humidity.

In the dormant condition, kumquats are very resistant to winter cold and they remain dormant also during relatively mild interludes. This makes the kumquats extremely important as breeding material for inducing cold resistance in Citrus species.

In South-East Asia kumquat is found only in a few fruit collections and home gardens in the highlands. Research on all agronomical aspects is needed to consider possibilities for commercial production on a larger scale.

Godden, G., 1988. Growing citrus trees. Lothian Publishing Company Pty Ltd., Melbourne.
Morton, J.F., 1987. Fruits of warm climates. Creative Resource Systems, Winterville, N.C., USA. pp. 182—185.
Swingle, W.T., 1967. Botany of Citrus. In: Reuther, W., Webber, H.J. & Batchelor, L.D. (Editors): The citrus industry. Revised edition. Vol. 1. History, botany and varieties. University of California, Division of Agricultural Sciences. Berkeley. pp. 328—339.

Nguyen Tien Hiep & P.C.M. Jansen

Hiep, N.T. & Jansen, P.C.M., 1991. Fortunella Swingle. In: Verheij, E.W.M. and Coronel, R.E. (Editors): Plant Resources of South-East Asia No 2: Edible fruits and nuts. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea