Citrofortunella microcarpa (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

×Citrofortunella microcarpa (Bunge) Wijnands

Protologue: Baileya 22(3): 134-136 (1984).

Family: Rutaceae

Chromosome number: 2n= 18

• Citrus microcarpa Bunge (1832),
• Citrus mitis Blanco (1837),
• ×Citrofortunella mitis (Blanco) J. Ingram & H.E. Moore (1975).

• Calamondin, China orange, golden lime (En)
• Calamondin (Fr)
• Indonesia: jeruk peres, jeruk kasturi, jeruk potong
• Malaysia: limau kesturi, limau chuit
• Philippines: kalamondin, kalamansi, limonsito
• Thailand: sommapit (Trat), somchit (Bangkok), manao-wan
• Vietnam: tâc, hanh.

The calamondin almost certainly originated in China as a natural hybrid between a sour, loose-skinned mandarin, probably Citrus reticulata Blanco var. austera Swingle and a kumquat, perhaps Fortunella margarita (Lour.) Swingle. It subsequently spread and was widely distributed in the Orient, especially in Indonesia and the Philippines, during early times. At present it is widely grown in India and throughout South and South-East Asia. It can also be found in Australia, Japan, the United States, the Bahamas, some islands of the West Indies and parts of Central America.

The calamondin is primarily valued for its acid juice. In the Philippines it is commercially processed into bottled concentrate and juice. It is made into marmalade, or preserved whole in sugar syrup. It is used in making chutneys and as a flavour enhancer for dishes comprising seafood or meat. The juice is used as a stain remover, body deodorant, skin bleach and hair shampoo. It is also used to treat skin irritation, as a cough remedy, an antiphlogistic, laxative and, when combined with pepper, it is prescribed to expel phlegm. The roots are used for a traditional treatment at childbirth, the distilled oil of the leaves to cure flatulence. Bees gather the nectar to make honey. The calamondin also may serve as rootstock for lemons and the oval kumquat. It is popularly used as a potted ornamental plant in many countries.

The only South-East Asian data on area under cultivation and production are from the Philippines where in 1987 11 420 ha were planted to 5 401 000 trees which yielded 51 291 t of fruit. From the Philippines, fruits are exported fresh and processed to Guam, Hong Kong, the Pacific islands and the United States. Israel now exports potted plants to the European market, where they are popular house plants.

Per 100 g edible portion, the calamondin fruit contains water 89.8 g, protein 0.4 g, fat 1.0 g, carbohydrates 8.3 g, ash 0.5 g; the energy value is 160 kJ/100 g. The vitamin C content of the whole fruit is 88.4-111.3 mg; 30-31.5 mg/100 g in the juice and 130-174 mg/100 g in the peel. The leaves contain about 1% volatile oil.

• Evergreen straight and columnar shrub or treelet, 2-7.5 m tall, with a long taproot; stem slender, slightly spiny, branches upright.
• Leaves alternate, elliptic to obovate, 3-8 cm × 1-4 cm, base acute, margins slightly crenulate, apex retuse, slightly notched or acute, glossy dark green above, pale green below, aromatic when crushed; petiole ca. 1 cm long, narrowly marginate.
• Inflorescences axillary, 1-3-flowered; flowers white, fragrant, 2 cm wide; calyx 5-toothed; petals 5, elliptic-oblong, 1-2 cm long; stamens 20, filaments united in a tube.
• Fruit a subglobose to globose berry, up to 4.5 cm in diameter, depressed or flattened at apex; rind greenish-yellow to orange-red, thin, loose, with numerous oil glands; segments 6-10, axis small, semi-hollow; flesh orange, tender, acid juicy.
• Seeds 0-11, obovoid, small, plump, usually polyembryonic.

Seeds germinate in 10-15 days. Stem elongation in the sexually propagated plant is initiated by terminal growth with subsequent sprouting of lateral buds. The formation of floral shoots puts an end to the extension of the axis and lateral shoots become the main mode of branching for the tree.

The tree flowers and fruits throughout the year, with a pronounced harvest season lasting for 3 months. The flowers are self-fertile. Fruits mature about 5 months from flowering. Clonal trees come into bearing 3 years after planting; seedlings after 5-6 years. At the age of 6 years, a calamondin tree may bear as many as 5000 fruits.

Some authors classify calamondin as a Citrus species. Recent arguments, however, imply that it is a Citrus × Fortunella hybrid, possessing the sour, loose-skinned character of the mandarin and the hardy nature of the kumquat; hence the hybrid generic name ×Citrofortunella J. Ingram & H.E. Moore. However, some forms (e.g. in Malaysia) are tight-skinned. The identity of the calamondin is not yet entirely clear and the correct name will have to be changed if Citrus madurensis Lour. (1790) is shown to be a calamondin too. An interesting cultivar found in Japan is the "Shikinari-mikan", a tetraploid with larger and sweeter fruit; it also tends to be more vigorous than the diploid calamondin. "Peters" is an attractive ornamental cultivar with variegated leaves, cultivated in California for landscaping purposes.

Calamondin thrives in warm climates but can also grow in cool but frost-free areas. Localities with an evenly distributed rainfall of 1500-2000 mm/year are ideal. Areas with long dry periods are equally suitable, provided irrigation water is available. Calamondin is predominantly grown in the lowlands. It can grow over a wide range of soil types from clay loam to limestone to sand. However, it performs best in a well-drained, sandy or clay loam soil rich in organic matter with a pH of 5.5-7.0. It is moderately drought-tolerant but cannot withstand strong winds.

The calamondin is easily grown from seed. Each seed contains 3-5 embryos, which produce true-to-type, spiny seedlings. Superior trees are propagated by stem cuttings, marcotting, budding or grafting. For large-scale multiplication, shield budding on calamandarin rootstocks, believed to be a hybrid between calamondin and mandarin, is practised in the Philippines. In the United States, particularly in Florida, large-scale propagation of calamondin for pot culture is done by rooting cuttings under constant mist.

To prepare seeds for planting, they are washed and sown in a seed-bed, 1-2 cm apart at a depth of 1 cm. After 4-5 months, when the seedlings are 10-15 cm tall, they are transplanted to the nursery or to individual containers. With proper care, seedlings will grow at the rate of 30 cm/year.

For field planting, the plants are set 4-6 m apart in a hexagonal pattern or in rows. Planting out is preferably done during the rainy season.

For optimum growth of one-year-old trees, 50-100 g of urea is applied per tree, increasing to 200-300 g per tree during the second year. When the tree starts bearing fruit commercially in the third year, 350-400 g of a compound fertilizer is applied, the amount increasing correspondingly as the tree grows bigger. The fertilizer is evenly distributed in two applications; the first application during the onset of the rains and the second application towards the end of the rainy season. Weeding under the trees helps to maintain tree growth. Pruning is limited to the removal of diseased and dead branches.

The most serious disease in the Philippines is leaf mottling, known internationally as greening, which is transmitted by the citrus psyllid Diaphorina citri. Certified disease-free planting material should be used, all infected citrus trees in the area should be grubbed and burned, and the vector should be controlled; there is no cure for diseased trees. The Mediterranean and Caribbean fruit flies account for the decline in the number of calamondin trees planted in Florida. Virus diseases include crinkly leaf, exocortis, psorosis and xyloporosis.

Calamondin trees can be forced to flower earlier by heavy watering 1-2 months before normal flowering time. Peak harvest season in the Philippines is from August to October, though fruits are available throughout the year. At harvest the fruit is either pulled off by hand or clipped with shears; it is carried in picking baskets.

At 3 years the tree may yield 0.75 kg; at 6 years 10 kg and at 10 years 50 kg. At 625 trees/ha an average yield of slightly more than 30 kg/tree suffices for a yield level of 20 t/ha.

In the Philippines, the general practice is to pack calamondin fruits in "kaings" (large bamboo baskets) lined with banana leaf-sheaths or newspaper; they are immediately transported to the market. If stored at 8-10°C and 90% relative humidity, the fruit keeps well for 2-3 weeks, the weight loss being limited to 6.5%.

Seeds are of no use in long-term germplasm conservation. A few accessions of living trees are available in collections in China, Colombia, Malaysia, the Philippines, Spain, Thailand and the United States.

The calamondin seed is polyembryonic. Genetic markers are needed to identify the zygotic seedling. Alternatively the zygotic embryo may be extracted from the seed and cultured in vitro. The possibility of breeding seedless triploids, using the tetraploid cultivar as a parent, deserves consideration. Useful budsports (mutations in a meristem giving rise to a branch with deviating characters) among nucellar seedling trees should also be exploited.

The potential of the calamondin lies in its varied uses. Once familiarity with the fruit is established in other countries, the scope for increasing production seems large.

• Coronel, R.E., et al., 1980. The Philippines recommends for Citrus. Philippine Council for Agriculture and Resources Research, Los Baños, Laguna. 63 pp.
• Galang, F.G., 1955. Fruit and nut growing in the Philippines. AIA Printing Press, Malabon, Rizal. p. 382.
• Hensleigh, T.E. & Holaway, B.K. (Editors), 1988. Agroforestry species for the Philippines. AIA Printers, Malabon, Metro-Manila. pp. 113-115.
• Morton, J.F., 1987. Fruits of warm climates. Creative Resource Systems, Winterville, N.C. pp. 176-178.
• Reuther, W., Webber, H.J. & Batchelor, L.D. (Editors), 1967. The citrus industry. Revised edition. Vol. 1. History, world distribution, botany and varieties. Division of Agricultural Sciences, University of California. pp. 337, 367, 531.

R.C. Sotto