Issue No 4, July 1995.

NOTICE: Hard copies of the Australian New Crops Newsletter are available from the publisher, Dr Rob Fletcher. Details of availability are included in the Advice on Publications Available.

14.1 Longan (Euphoria longan)

The longan is closely related to the lychee and is similar in growth and fruiting habit. The tree is tougher and less demanding, with respect to climate and soil conditions, than the lychee and it fruits in cooler and drier areas. However, the exact environmental conditions required for high yields are not well defined.

The longan is a medium to large (10 to 20 m tall) evergreen tree with a dense canopy, brittle wood and corky bark which splits and peels. Tree shape depends on the cultivar and varies from erect to spreading. The inflorescences are large (30 to 50 cm long), multi-branched and leafless. They are borne on new growth produced during mid-summer or autumn. The flowers are small, inconspicuous and yellow brown. The fruit are similar to those of lychee in structure, but are smaller, smoother and yellow-tan in colour. The word 'longan' comes from the Chinese and literally means 'dragon-eye' which is an apt description of the fruit after the skin has been removed. The fleshy aril is white to off-white or pinkish in colour and surrounds a red brown, brown to black seed which separates easily from the flesh. The fruit are milder in flavour and less acidic than lychees.

The longan originated in China or in the area between Burma and India. Thailand, China and Taiwan are the main centres of commercial production. In Thailand, production is centred in the tropical monsoon areas of Chiangmai, Lamphun and Phrae at elevations between 300 and 600 m above sea level. The main production centres in China are in the Fujian and Guandong provinces. In Fujian province, longan is second in importance to citrus and is grown in cooler subtropical areas.

The lychee fruit can be eaten fresh, frozen, dried or canned. Thawed fruit can be used in the same way as freshly picked fruit without any loss of colour or flavour. The fruit can be peeled, pitted and canned and the juice of most cultivars is sufficiently sweet for the fruit to be processed without adding sugar. Canned longans are very acceptable and the taste is considered better than canned lychees.

Longans in Thailand and China flower during the period December to March (the equivalent of June to September in the Southern Hemisphere) with the fruit maturing from July to September (equivalent to January to March in Australia). At Cairns in north Queensland, longans flower later than in Nambour in south-east Queensland but the fruit develop faster and are harvested from mid-January to mid-March at Cairns and from late February to early April in Nambour. The differences in times of flowering and fruit maturity are due to differences in rainfall and in day and night temperatures.

Longans require a period of low minimum temperature to induce panicle and flower initiation. However, they are sensitive to frost and are killed or severely injured by prolonged temperatures below freezing. Cultivar differences in cold tolerance have been noted in China.

Productivity of longan is closely linked to climatic conditions during flowering and fruit maturation. Longan can survive droughts but adequate water is required for good production. Excessive rainfall during flowering causes flower drop and prevents pollination and fruit set. Overcast weather before harvest induces fruit shedding. Longan are sensitive to wind damage and strong cyclonic winds can cause branch splitting and fruit shedding.

The best growth and cropping of longan is achieved on deep, well drained fertile soils with a pH of 5.5 to 6.0 and low salinity. In Thailand, the highest production is usually obtained on heavy alluvial soils with access to the water table. In eastern Australia, the preferred soils for longan growing are heavy, fine textured soils and red loams with high fertility and good water holding capacity.

There is considerable genetic variability in longan cultivars with marked differences in bark characteristics, yielding ability, disease and wind resistance, fruit size, flesh recovery and eating quality, tree size, shape, and canopy density, leaf size, leaf colour and arrangement.

The market demand is for large fruited cultivars with high flesh recovery, crisp sweet flesh and good flavour. Breeding and selection programs have been largely directed at resolving problems of biennial bearing and small fruit size. Most of the important longan cultivars from the major longan growing areas of the world have now been introduced into Australia by the Queensland Department of Primary Industries and have been evaluated at Kamerunga and Walkamin in northern Queensland, at Nambour in south eastern Queensland and at Alstonville in northern NSW. A number of cultivars have yielded 40 to 55 kg per tree by year six.

Longans are readily propagated from seed but the preferred method of propagation in Thailand is air layering (marcottage) although grafting, inarching and cuttings are all possible. In Fujian Province in China, propagation by air-layering has been practised for over 800 years and a success rate of 80 to 90% is claimed by Chinese nurserymen. In Australia, longans have been successfully propagated by grafting with budding, and whip and tongue as the preferred methods.

Longans are grown at tree densities of 50 trees/ha in mature orchards in Thailand to about 300 trees/ha in high density plantings in Taiwan. Tree densities in Fujian province range from 195 to 300/ha with an average around 270 tree/ha. Higher density plantings (6 by 6m spacing) are likely to be more profitable, provided young trees bear fruit and the fruit fetches reasonable prices. Well grown trees fill their space in 6 to 7 years. Pruning of tops and roots can extend the life of high density plantings up to about 15 years before some tree removal becomes necessary. Judicious pruning is required and assists in the formation of well formed tree crowns, strengthens fruit bearing branches, ensures annual cropping and limits insect pests and diseases.

In newly established orchards young trees should be grown as vigorously as possible for the first four years to attain the greatest tree size and bearing surface. Vigorous growth is achieved by regular applications of water and nutrients, strategic pruning and protection from frost, wind, weeds and pests. After four years, the application of nitrogen should cease until the first crop is picked.

Longan in Queensland is relatively free of pests, compared with lychees, but a number of insect pests do attack the crop. These include scales, aphids, stem borers, leaf eating caterpillars, flower caterpillars, mealy bug, fruit spotting bug, stink bug, macadamia nutborer, elephant beetles and fruit piercing moth. Fortunately, effective control measures are available for all but the last two pests. Early harvesting of the fruit is the only practical method of limiting the damage from these two pests.

There are no major diseases limiting longan production in Australia. Weeds can reduce tree growth and need to be controlled with herbicides such as paraquat and glyphosate.

Longans do not ripen off the tree and maturity is judged by the particular shape, skin colour and flavour of each cultivar. Most fruit can be picked from a tree in one harvest and from a single cultivar in an orchard within two weeks. In order to spread the workload in a commercial orchard it is essential to plant a range of cultivars having different maturity times in any one orchard.

Fruit are harvested by removing the whole cluster plus one or two leaves. In Australia, fruit are then clipped from the panicles, sorted for size, insect damage and skin blemishes and placed in bulk trays. Fruit subjected to hydrocooling or forced air cooling maintain acceptable eating quality for up to three weeks at 7.5°C and 90% relative humidity. In Thailand, most fruit are marketed in branches on the fruit stalk in 22 to 24 kg baskets and consumed within three days of picking, without any postharvest treatment.

Commercial orchards in Queensland mainly use the cultivars Kohala, Homestead No.1, Chompoo, Haew and Biew Kiew. The total area planted to longan in Queensland is estimated at 200 ha with the oldest orchards now 10 to 15 years old. The limited data available indicate that yields of 25 to 80 kg per tree are being obtained after year ten.

The main problems experienced in commercial orchards have been irregular flowering, biennial bearing and small fruit. Trees tend to overcrop some years and this is followed by a light crop the next year.

The potential market for longan in Australia is unknown as the taste is an acquired one. However, the demand from ethnic Asians within Australia currently far exceeds the supply. Market development in Australia will depend on the availability of good cultivars, the continuity of supply and promotion activities. The export possibilities appear particularly promising with Australia in a position to sell longan out of season in the main Asian markets of Hong Kong, Singapore and Malaysia. However, if these markets are to be successfully exploited guaranteed supplies of high quality fruit will be required.

While the demand for longan both locally and in overseas markets has yet to be fully evaluated, the prospects appear promising. Longans have a number of attributes which favour its commercial development in tropical and subtropical eastern Australia. However, there are also a number of limitations which growers need to consider before embarking on large-scale longan cultivation.

Contact: Dr Rob Fletcher, School of Land and Food, The University of Queensland Gatton College, 4345; Telephone: 07 5460 1311 or 07 5460 1301; Facsimile: 07 5460 1112; International facsimile: 61 7 5460 1112; Email: r.fletcher@mailbox.uq.edu.au

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originally created by: GK; latest update 6 June 1999 by: RF