Ravie Sethpakdee 
The first record about lychee in Thailand was dated back to the year 1854 (King Rama IV). However, introduction of lychee to this country must be earlier than 150 years ago. It is very likely that the lychee fruit first came along with Chinese traders and immigrants during the Ratanakosin Era (since 1782). Some trees which are older than 100 years still exist in Samut Songkhram province. Also, in the two eastern border provinces of Trad and Chanthaburi the native lychee called Seeraaman is found in the dense tropical rainforest. The diameter of these trees is usually greater than 1 m and they rarely bear fruit. Whether this lychee tree is an indigenous plant or left over from old settlement is very difficult to ascertain.
Lychee seems to have been introduced to this country via two major routes: by sea along with the Chinese immigrants and traders and by land with the hill tribe people. The first route could date back two centuries and lychee probably came in the form of seeds from imported fruit as well as accompanied seedlings. These lychee trees were able to adjust to the tropical climatic conditions, therefore the cultivars were named according to domestic language. Cultivars that came by the northern land route, probably from South China several decades ago, could have been in the form of marcottages. Names of these lychee cultivars have remained in Chinese.
Lychee production in Thailand can be divided into two planting types: (i) lowland or raised-bed type, and (ii) upland type. Trees of both planting types usually set fruit after 3 years. Thailand has an advantage in a longer production period of up to 3 months. Earliest harvesting can be from mid-March through last fruiting in mid-June.
Flowering and fruiting of lychee varies from year to year. Nonetheless, climatic influence, especially temperature, remains the major threat to lychee production throughout the country
2. PRESENT SITUATION OF LYCHEE CULTIVATION IN THE COUNTRY
Lychee growers in Thailand are smallholders with lychee planting ranging from a few trees to orchards of a few hectares. Upland growers may possess up to several thousands trees, however, such growers are few in number. Production zones are located in the central lowlands, and uplands of both the eastern and western regions. Most are concentrated in the north. Chiang Mai (8,322 ha) and Chiang Rai (5,763 ha) are the two major provinces that contribute more than 60 percent of the overall acreage (22,937 ha).
Statistically, the production yield showed an increasing trend from 1996-2000 except for the 1998 crop year, which was affected by the El Nino phenomenon (Figure 1). During the last cropping year (2000), a long period of low temperature resulted in a bumper crop (81,388 MT). However, Sub-zero early morning temperature with frost was observed in several northern provinces resulting in small-scale shoot injury.
Figure 1. Lychee Production Statistics of Thailand (1996-2000)
Lychee cultivars growing in Thailand can be divided into 2 groups based on their cool temperature requirements.
(i) Moderately low temperature cultivars: Cultivars in this group normally possess Thai names and are grown mainly in the lowland and the central area (including eastern and western regions). Adaptability of these cultivars to the local climate is probably the main season. More than 10 cultivars have been recorded but the most famous one is the Kom (dwarf) cultivar due to its compact canopy size. Other cultivars of less importance are Kra-lok Bai-Yaw, Sampao Kaew, Sa-rack Tong, Jean, Jean Yak, Tai, Tai Yai, Chor Rakum, Kiew Waan, Dang Payom, Kratone Tong Pra-rong and Kra-lok Bai Dum. Recently, Pantip lychee variety emerged and is grown mainly in Kanchanaburi province.
(ii) Low temperature cultivars: There are a few cultivars in this group which are grown mainly in the north. The lowest temperature requirement belongs to Hong Huay, which contributes more than two-thirds of the whole group. This is followed by Chakrapad, Kim Cheng, O-Hia and a few other less important cultivars. Chakrapad usually fetches the highest price due to its larger fruit size.
3. PRODUCTION OF PLANTING MATERAL
Air-layering or marcotting is the only method used in propagation. Growers and private nurseries are the major source of planting material. A few Government agencies provided cheaper as well as free of charge planting material to small-scale growers.
4. ESTABLISHMENT OF ORCHARDS
In the lowlands of the Central Plain the raised-bed or ridge system is generally used to grow lychee as well as other crops. Each bed is 4 m (sometimes 6 m) wide alternating with a 2 m wide ditch. The water level is kept constantly at 50 cm and controlled by an outer dyke. Irrigation and chemical sprays are employed by boat through the ditches all over the orchard. Coconut, pomelo, banana and other crops are planted along with the main lychee trees. Planting distances range from 3, 4, 5, 6 or 8 m apart depending upon the growers preference.
A square planting system is mainly employed in the upland orchards, but some new growers have switched to a rectangular system. Spacing of older orchards can be as wide as 10-12 m, but 5, 6 or 8 m are the most preferable. No orchards use the high density planting (HDP) system.
The technically recommended pit size is 1 x 1 x 1 m, but growers usually reduce this size to 0.8-0.5 m in both lowland and upland types. As much as one-half of the pit volume of farmyard manure or compost is incorporated during preparation. The Planting season starts from May at the onset of the Southwest monsoon. Sufficient rain minimizes the mortality rate and replanting chore.
5. CARE AND MANAGEMENT OF ORCHARDS
Training and Pruning of Plants
No exact training system is used but the tree is likely to become a modified leader type. A bush type, without main trunk, is frequently found among older lychee trees. Pruning usually done only on the inner, shaded twigs and branches. This practice results in uncontrolled canopy size. In order to reduce the tree size and height some growers employ a stub pruning method. Hard pruning of both the height and 4-sided perimeter is also practiced in some orchards. Recently, top opening of centre branches between 1-1.5 m wide has become a common practice among growers.
Application of Manure and Fertilizers
Farm manure as well as plant residues (peanut husk, rice straw), compost and chemical fertilizers are applied annually. The exact amount of manure applied is not known. Foliar fertilizers are added to every spray programme along with soil application. Use of foliar fertilizers is not only as a soil supplement, but also regulates tree growth and development. Since lychee growers believed that phosphate fertilizer stimulates tree flowering high P formulae are frequently used. The common NPK+Mg formulae used are 8:24:24, 9:25:25, 15:15:15, 16:16:16, 25:7:7, 13:13:21, and 12:12:17+2. Up to 10-12 kg per tree per year seems to be common. Mono-potassium phosphate or MKP (0:52:34) 0.5 percent is being used to inhibit undesirable flush during the flowering induction period. Beside manure and fertilizers other chemicals, such as seaweed extract, trace elements, polysaccharides etc., are also added.
Control of weeds has to be done several times during the rainy season. Both mechanical and chemical control measures are almost equally employed. Two main herbicides commonly used are glyphosate and paraquat.
Mulching is normally practiced during the dry season, which coincides with fruit setting and fruit growth period. Mulching can prevent fruit cracking due to fluctuation in soil moisture content. Rice straw and dried grass are the two main sources of mulching material. No plastic film mulching has been used.
The older and cheaper method of flood irrigation is practiced in the older orchards. Irrigation sprayed from a boat is commonly used in the raised-bed plantations. No irrigation system is employed on the higher slopes of the northern hilly areas. Modern orchards have switched to the mini-sprinkler system, which has been found to be more reliable. Several commercial growers have practiced Fertigation along with this irrigation system.
Control of Pests, Diseases and Physiological Disorders
Among insect pests a few are seriously threatening lychee growers. They are the fruit borer (Conopomorpha sinensis), longan sucking bug (Tessaratoma papillosa), fruit piercing moth (Othreis fullonia), twig borer (Zeuzera coffeae) and leaf miner (Conopomorpha litchiella). All of these pests can infect the longan as well as lychee (the acreage of longan is more than 100,000 ha or about 5 times that of lychee). This provides a longer host range from May-September. The fruit borer has a devastating effect in some years. Other insects occasionally threaten lychee, such as the leaf eating caterpillar (Oxyodes scrobiculata), scale insects and mealy bugs. Even though they are not of much concern, the lychee rust mite (Aceria litchii) or erinose mite can damage all newly flushed shoots of neglected trees.
Control of these pests essentially requires integrated management. Chemical sprays along with mechanical methods e.g. bagging, light-traps, pruning and other biological control strategies must be eventually incorporated.
Diseases in lychee can infect the leaf, branch, flower and fruit. The important ones are fruit rot (Peronophythora litchii), leaf spot (Lasiodiplodia theobromae), and sooty mold (Capnodium sp.). The leaf spot disease is also able to infect the fruit at the post-harvest stage causing fruit rot.
Sunburn, fruit cracking and undeveloped seeds are the major physiological disorders. Sunburn poses a threat to growers almost every year. Normally, the southwest face of the tree is prone to sunburn. Damage to the late blooming panicles from late February-March usually affects more than one-half of the tree. The time of fruit colour change (about 1 month before harvest) is the most vulnerable stage for cracking (splitting). Fluctuation in soil moisture content and a wider range of dry and wet regimes encourage more fruit cracking. Total crop loss has been observed in a non-irrigated tree after heavy rainfall. Undeveloped seed, an undesirable parthenocarpic fruit, is found mainly among the lowland cultivars such as Kom. This phenomenon occurs during a crop year with a cool climate after fruit set has taken place. Probably, the cold temperature has a lethal effect on the young and tender embryo.
6. HARVESTING OF FRUITS AND YIELDS
The harvesting season starts from mid-March in Chanthaburi followed by Samut Songkhram (early to mid-April) and Kanchanaburi (mid-late April). These early cultivars are of the lowland Kom and Pantip type. The northern lychee ripens almost 2-4 weeks later than the moderately low temperature cultivars from mid-May through mid-June. Hand picking is the sole harvesting method. Fruit skin must be stretched out almost to its limit at the time of harvest to ensure fruit maturity. Bagging is also practiced in several commercial orchards in order to protect the fruit from pest damage. Newsprint, and other types of paper are used as bagging material. HDPE bags with open ends have been used for bagging in Chiang Mai. This bagging method creates a micro-climate inside the bag. Even fruit colouring as well as size was observed from this bagging method.
Average yield of Kom and Hong Huay in a regular crop year ranges from 4.3-5 MT per hectare. Prices vary from year to year depending upon several factors.
Lychee fruit deteriorate rapidly from both desiccation and fungal infection. Pre-cooling with ice-water is a common practice in order to prevent post-harvest loss. Currently, fruit is packed in 10 kg cartons lined and covered with leaves. Sulphur dioxide treatment has been used to stabilized skin colour and prevents mold infection.
Exporters and middlemen have the greatest influence on the marketing system. Temporary packing houses with a fruit buying post are set up by the exporters. Distribution of fruit depends on the individual traders channels. Export of lychee to Malaysia and Singapore is by land but export over longer distances, such as Hong Kong and European countries, is by air cargo. The below grade fruit is sold as raw material for processing. Export of fresh and canned lychee from 1995-1999 is shown below.
In 1999 Hong Kong was the largest importer of fresh Thai lychee (8,644 MT), while Malaysia and USA were the major importers of canned lychee (3,767 and 2,049 MT, respectively).
8. POTENTIAL FOR LYCHEE PRODUCTION DEVELOPMENT
Currently, Thailand is ranked among the worlds major lychee exporting countries. There are several advantages for lychee production development, as follows.
i. Cultivar: Thailand has a wide range of cultivars especially of the moderately low temperature type. Selection of these cultivars for a particular location and/or purpose is highly feasible.
ii. Geographic location: With the production areas ranging from the tropical lowlands to the sub-tropical climate of the highlands of the north and northeast regions, the fruiting season could lengthened up to a full 3 month period. There are several areas where selected cultivars could fill up any gap of supply throughout this 3 month period. Thus better confidence in supply could strengthen marketing planning strategy.
iii. Agricultural materials: The supply of agricultural materials such as fertilizer, plant growth regulators, chemicals, etc., is abundant and easy to access. This would enhance and facilitate any production development.
9. CONSTRAINTS IN LYCHEE PRODUCTION DEVELOPMENT
There are several problems that either inhibit or restrict lychee development in the country as follows:
i. Alternate bearing habit: Growers are tired of the flowering uncertainty of their crop. Climatic conditions play an important role in each cropping season.
ii. Perishable nature: Lychee fruit is considered to be a highly perishable crop. Fruit deteriorate rapidly after harvest hence it has a very short shelf-life.
iii. Poor marketing management: Almost all lychee marketing is under the control of middlemen and exporters. Growers have very low bargaining power in order to get a better price.
iv. Low fruit quality: Poor lychee growers are unable to invest in agricultural materials such as chemical fertilizers, which results in low quality fruit. Such poor quality crops could bring down the overall price.
v. Longan mania: High demand for longan from China during the last few years pushed the longan price ahead of lychee. The situation worsened with the discovery of the use of chlorate in forcing longan to flower. Currently, growers can bring the longan trees to flower at will with chlorate application. Consequently, lychee is no longer a favourite crop for growers. Some plantations in the north replaced lychee with either longan or the more profitable mandarin citrus.
10. GOVERNMENT POLICIES AND PLANS FOR RESEARCH AND DEVELOPMENT OF LYCHEE
The Thailand Research Fund (TRF) has been organized and has provided funds to about 6 research projects in lychee since 1996. Chiang Rai Horticultural Research Centre is authorized by Department of Agriculture, Ministry of Agriculture and Cooperatives, to handle all the lychee projects under their guidance. Several academic institutes such as Chiang Mai University, Kasetsart University, etc. have also carried out their own research. However, the present economic circumstance coinciding with longan mania has resulted in sluggish lychee production development.
Lychee has been grown commercially in Thailand for more than 100 years. There are two types of cultivars that exist in Thailand: (i) the moderately low temperature cultivars which mainly grow in lowland and central areas, and (ii) the low temperature cultivars that grow in the uplands of northern provinces.
Under present circumstance several problems remain, namely: (i) control of flowering, (ii) nutrition and (iii) post-harvest treatment.
Alternate bearing in lychee remains a big task for physiologists around the world. The El Nino effect resulted in a poor harvest of only 40 percent. There is no single solution in lychee flowering control. Climatic conditions, especially inadequate cold temperature may cause poor flowing in such years. However, manipulation of several events such as shoot maturity, irrigation, cold spell, tree health, and bud breaking must be well organized with proper synchronization.
There is no proper recommendation on lychee nutrient requirements. Insufficient and improper fertilizer application may result in lower crop yield and poor fruit quality. Currently, a research project on a nutrient analysis system is funded by TRF.
Fumigation with sulphur dioxide has been used in colour stabilization as well as fungal inhibition in lychee in recent years. Treated lychee fruit can retain its shelf-life much longer in cold storage. However, improper use may result in higher residues of SO2. All of this could be regulated under a quality assurance system.
 Head, Department of
Horticulture, Faculty of Agriculture, Kasetsart University, Kamphaengsaen
Campus, Nakhon Pathom, Thailand.|