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9. DECIDUOUS FRUIT PRODUCTION IN THAILAND

Suranant Subhadrabandhu*

* Professor, Department of Horticulture, Faculty of Agriculture, Kasetsaart University, Bangkok, Thailand.
1. INTRODUCTION

Deciduous fruits, sometimes referred to as temperate-zone fruits, are in heavy demand in tropical countries. The interest in these crops is on the rise. Shortages in hard currency in most tropical countries reduces their import and encourages attempts at local production.

In Thailand, deciduous fruit production has been focused in the Northern region which represents one of the most important areas of the country from the standpoint of socio-economic, agro-ecological and political considerations. The region accounts for about one-quarter of the country’s forest area, and the majority of hill tribes live in this region. The population of the hill tribes has been growing rapidly, causing expansion of slash and burn agriculture as well as shifting cultivation of the opium poppy in the region. This situation has caused damage to natural resources in the form of soil deterioration, flooding in wet periods and critical water shortages in the summer months (Subhadrabandhu and Punsri, 1987). In an effort to improve the highlands, deciduous fruit crops were introduced as substitution crops and are expected to serve as the main source of income for the hill tribes. Perennial fruit trees are believed to have great potential in the highland areas of Northern Thailand, both commercially and socially, as they can provide a steady and reliable income to the hill tribe farmers. If successfully established, these trees will eventually minimize the practice of shifting cultivation by encouraging more permanent settlement of hill tribe people and may curtail the growing of opium poppy. Furthermore, planting of fruit trees is an acceptable practice in reforestation and conservation programs, thus rendering an overall improvement to the environment. However, at present there are many limitations confronting the production of high quality deciduous fruits in Northern Thailand. The problems include among others, lack of suitable cultivars, insufficient chilling and improper cultural practices.

2. SITUATION OF DECIDUOUS FRUIT CROP CULTIVATION

2.1 Peach and Nectarine (Prunus persica L. Batsch)

Peach and nectarine are some of the deciduous fruits that receive much attention for growing in the highland areas of Northern Thailand. Previous reports on the performance of the introduced cultivars were documented (Subhadrabandhu, 1981, 1987). In the highlands of Northern Thailand, peach trees have been grown by hill tribes for many centuries. It is believed that the trees were brought in by villagers migrating from China (Subhadrabandhu, 1973). Over many centuries, the peach trees adapted to the growing conditions in the highland areas by the process of natural selection, resulting in the variety being known as ‘local’ peach. These peaches produce small, low quality fruits that could be eaten fresh. They are cling stone types and the hill tribe growers can only sell the fruits at rather low prices to the processing factories for processing into pickles. Therefore, many peach cultivars of low chilling requirement and having better quality for fresh consumption, have been introduced for testing their performance in the highland areas of Northern Thailand using these local peaches as rootstocks (Subhadrabandhu, et. al., 1989).

At present, the introduced peach cultivars that have been tested in Northern Thailand and have been extended to hill tribe communities for cultivation are Early Grande, Flordabelle and Flordasun. The average yields of these cultivars exceed 10 kg/tree when over 4 years of age. The average price that the growers receive was about 30 baht per kg (the price varies according to the size of fruits). Thus, the growers can obtain at least 300 baht/tree. The common spacing for peach is 8 × 8 m or 156 trees per hectare, giving an income of about 46,800 baht/hectare (Table 1). Thus, the income received from growing peach is very good compared to what they used to receive from growing opium poppy.

Some nectarine cultivars such as Sundowner and Fla 5-14 seemed to be well adapted (Subhadrabandhu, et. al., 1989). However, more studies are needed before they can be distributed to growers. Both peach and nectarine cultivars are propagated on the seedlings of local peaches. The production is satisfactory when they are grown in the highland areas of 1,000 m a.s.l. and above in the Northern Thailand areas of Chiang Mai, Chiang Rai and Mae Hong Son provinces. The area under cultivation for peaches and nectarine was about 16 hectares in 1997 with a total production of about 60 tons (Table 2). This figure is in addition to the production of local peaches used in processing factories.

2.2 Japanese Apricot (Prunus mume Siebold & Zuccarini)

This plant is native to China, Japan and probably also to the northern parts of Laos and Vietnam (Subhadrabandhu, 1991). It is also cultivated in Northern Thailand, but not elsewhere in South-East Asia. Japanese apricots are eaten in Japan, China and Thailand as pickles and preserves. The fruit trees are extensively grown in Japan, China and Korea. Japanese apricots have been cultivated in lowland areas of Northern Thailand for 30-40 years (Punsri, et. al., 1982). Presently, a local variety is found growing as a home garden crop in some villages of Chiang Rai province. It is fast-growing and thrives in poor soil, but the fruits are rather small and of inferior quality. It can be, however, used as a rootstock for introductions (Subhadrabandhu and Punsri, 1987).

Seven cultivars from Japan (Shirakaga, Bungo, Koshyukoume, Koshukuome, Koshuko, Baigo and Kobai) were tested in the highlands of Northern Thailand. After 4-5 growing seasons, their performance was very poor and the trees showed signs of insufficient chilling. They were removed from further study. Two other cultivars, Ping Ting and Jen Tao, were introduced from Taiwan. These two cultivars grew very well under our highland conditions (Table 1). They produced fruits after the fourth year. The average yields of 5-year old and 10-year old trees were 40 and 100 kg/tree respectively. At present, these cultivars are propagated by stem cuttings and marcotting and distributed to hill tribes. In 1997, the production of Japanese apricot was 334 tons covering an area of 42 hectares (Table 2).

In Thailand, hill tribe farmers sell their Japanese apricot fruits for pickles, at the price of about 10-15 baht/kg. The fruits are processed into salted pickles, which are commonly used for cooking. Some fruits are made into Japanese apricot juice which is a popular drink.

Table 1. Average Yield and Estimated Income from Recommended Species and Cultivars of Deciduous Fruits in Thailand (Subhadrabandhu and Punsri, 1987)1/

1/ Estimated for 6-10 years old trees, based on the data from 1980-1984.

Species

Cultivars

Av. Yield
Per Tree
(kg)

Plant
spacing
(m)

Net Price2/ of
Fresh Fruit
(US$/kg)

Income
from 10
Trees (US$)

Japanese Apricot

Ping Ting
Jen Tao

80

10 × 10

1.20

960

Peach

Early Grande
Flordabelle
Flordasun
Ying Ku

25

8 × 8

1.60

400

Apple

Anna
Ein Shemer
Dorsette Golden

8

3 × 3

2.40

192

Asian Pear

Yogoyama
Wase
Song Mao
Pien Pu
Pathanak

100

10 × 10

1.60

1600

Persimmon

Astringent

20

6 × 6

1.40

280

2/ The price is variable, this is estimated in 1984 value.

Table 2. Production Statistics of Deciduous Fruits in Northern Thailand in 1997

Species

Number of
Bearing Trees

Acreage
(ha)

Total Yield
(tons)

Japanese Apricot

4,174

42

334

Peach

2,433

16

61

Plum

3,798

25

114

Asian Pear

2,445

25

245

Persimmon

6,167

23

124


2.3 Asian pear (Pyrus pyrifolia (N.L. Burman) Nakai)

This species originated in North-East and East Asia; wild plants occur in the Sechuan region of Southern China (Oyen, 1991). Asian pear was first cultivated in China and Japan, which are still the centers of production. Commercial production has spread to Korea, Taiwan and more recently to the United States, Australia and New Zealand. Scattered trees and small orchards of Asian pears are found in most tropical highlands in South and South-East Asia, mainly in North Thailand and the drier parts of Indonesia and the Philippines.

In highland areas of Northern Thailand, the European pear (Pyrus communis L.) grew poorly due to insufficient chilling. Only a few buds opened and a few leaves were produced in a year. Most died in the nursery. Therefore, researchers turned their interest to low chilling cultivars of Asian pears, and a total of 31 cultivars of Asian pears were introduced from Taiwan, Japan and India. Among these introduced cultivars, Yokoyama Wase, Pien Pu, Song Mao and Pathanak had the best performance. The first three cultivars were introduced from Taiwan and the last from India. These cultivars yielded satisfactory crops under highland conditions, but the eating quality of the fruit is inferior when compared to the popular high-chilling Asian pears such as Kosui and Hosui from Japan. At present, the low chilling cultivars are being propagated by grafting onto rootstocks introduced from both Taiwan and India. The grafted trees are distributed to hill tribe growers. In 1997, the production of Asian pear in Northern Thailand amounted to 245 tons and occupied an area of 25 hectares. Most of the Asian pear is sold as fresh fruit and the price varies from 20-50 baht/kg.

2.4 Japanese Plum (Prunus salicina Lindley)

This fruit species originated in China and has been cultivated there and in Japan since ancient times. It is now grown worldwide, mainly in the subtropics and tropical highlands. In highland areas of Northern Thailand, low chilling cultivars of plum have been introduced alongside with low chill peach and nectarine, mainly from Taiwan and Florida. These plums are grown on local peach stock at the present time. After a few years of testing their performance, three cultivars from Taiwan and one cultivars from Florida (Gulfruby) gave satisfactory yields. The fruit quality is acceptable to Thai consumers. They are distributed to hill tribe growers, 2-3 cultivars to each grower as the Gulfruby plum is self-unfruitful and need pollen from the Taiwan cultivars for successful fruit set. At present, the introduced Taiwanese plums do not have a proper name; they are known as Ban Luang Red (red flesh) and Ban Luang Yellow (yellow flesh).

In 1997, the production of Japanese plum in Northern Thailand amounted to 114 tons and occupied a growing area of 25 hectares. About 80 percent of the production was sold as fresh fruit while 20 percent was sent to factories for making plum juice.

2.5 Persimmon (Diospyros Kaki L.F.)

The persimmon is one of the classical fruits of China, from where it was introduced in ancient times to Japan. China and Japan are the main areas of commercial cultivation but smaller centers have developed in Italy, Israel, Brazil, California (U.S.A.), Australia and New Zealand. In South-East Asia it is grown on a limited scale in Java, Sumatra, Malaysia and Northern Thailand.

In Thailand, about 50 cultivars of persimmon were introduced from Taiwan, Japan and California. They were tested for their performance in the highland areas. After six years of study, only one cultivar of non-astringent persimmon produced fruits of satisfactory quality, but with rather poor yield. It was later found that the low yield was due to lack of pollinators, as most of the non-astringent persimmon cultivars need pollen from other cultivars for good crops. Many astringent cultivars bear good crops but the fruits have to be treated, to get rid of astringency, before sending them to the market. At present, due to the high yield, astringent persimmons, such as Tanenashi, Nightingale, Szu Chou, Xichu, Hachiya, Thien Shan and Ang Sai have been released to hill tribe growers, along with techniques to reduce astringency. These persimmon cultivars are grafted or budded on D. glandulosa and D. lotus stocks which are commonly grown in these areas.

In 1997, the production of persimmon in Northern Thailand amounted to 124 tons, and occupied an area of 23 hectares (Table 2). Almost all of the fruits were sold as fresh fruits while a very small amount was used for experimentation for producing dried persimmon.

2.6 Apple (Malus domestica Borkh.)

This is the most well known deciduous fruit crop. In South-East Asia, apple is commercially grown is East Java, Indonesia, which produced 50,000 tons from 7.6 million bearing trees in 1988 (Kusumo and Verheij, 1991). Apple growing proved to be successful at high altitudes in Northern Thailand and is gaining popularity in the Philippines.

In Thailand, 45 cultivars of apple were introduced and the overall growth was observed for five growing seasons. Low chilling cultivars such as Anna, Ein Shimer and Dorsett Golden grew well at Royal Ang Khang Station at an altitude of 1,400 m.a.s.l (Subhadrabandhu and Punsri, 1986). These cultivars seemed to have no problem in floral bud initiation. They flowered readily and the fruit set was satisfactory. However, fruit set of Anna was much better if cross pollinated with Dorset Golden or Ein Shimer.

Due to the long storage ability of high quality apple from the high chilling cultivars grown in U.S.A, Australia, New Zealand and China, imported apple fruits are commonly sold in local markets of Thailand at rather low prices. This makes the production of apple in the highland areas not so attractive to hill tribe growers as they can only sell their fruits at rather low prices in order to compete with imports, whereas the cost of production is almost the same as the other deciduous fruits. Because of this reason, extension of apple cultivation by the hill tribe growers has ended, and research work on apple has been suspended.

3. PRODUCTION OF PLANTING MATERIAL

The highland areas of Northern Thailand are the main areas where deciduous fruit trees are grown. These areas cover the head watershed areas in the North of Thailand where, in the past, dense evergreen forests were found and had been the main water supply catchments to the lowland in the North itself as well as the central region through to Bangkok. The situation has now changed, and at present only about 20 percent of the mountainous land of the North remains as forest. The majority of the hill area has been destroyed by the traditional practices of shifting cultivation by tribesmen living in these hill areas. Recently, it was estimated that at least 700,000 tribesmen are living in the highlands of Northern Thailand which cover many watershed areas (Subhadrabandhu, 1984). These people normally grow annual crops such as upland rice and corn for their own food and their main cash crop is opium poppy, the crop that has high notoriety world-wide. In general, these people are poor and have a difficult existance. His Majesty the King is the first to display a willingness to help these people by setting up the Royal Project (now named the Royal Project Foundation) which aims at minimizing hunger among these tribesmen (Bhisadej Rajani, 1977). The main purpose of the Royal Project is to help these people to produce enough food or to produce enough income from agricultural crops, in place of opium poppy, in order to attain a reasonable standard of living. Thus, deciduous fruit is one of the most sensible replacements decided by local agricultural diversification planners.

Under Thai Law, the lands in any watershed areas are preserved and protected from any private ownership. The hill tribes, having lived in the areas for centuries, are allowed to stay on but, legally, they have no ownership or rights to the land, and the government wants them to practice settled agriculture without moving around. The Royal Forest Department has the task of looking after these watershed areas.

For the above reasons, there are no private nurseries producing planting materials of deciduous fruit crops in these areas. Also, due to the tight governmental budget, there are no governmental organizations responsible for producing these plants. The planting materials are produced by the Royal Project Stations scattered among villages in these areas. At the beginning, budded and grafted plants were planted in the stations in experimental plots. Their yield performances and the income from selling the fruits were recorded. The better cultivars were then made ready for distribution to hill tribe growers.

As for extension work, in the first phase of the project, the grafted and budded plants were provided to hill tribes. Local peach seedlings were used as rootstocks for peach, nectarine and plum. Local Japanese apricot seedlings from the Chiang Rai area were used for Japanese apricot together with Japanese apricot plants from marcotting and stem cuttings. For Asian pear, the seedlings from rootstock plants of Indian and Taiwanese origin were used. Diospyros glandulosa and D. lotus seedlings were used as rootstocks for persimmon. MM 106 was used as a rootstock for apple. However, when more hill tribe growers joined the project and needed more planting materials, only stock plants (ungrafted plants) were provided to them, and later they were grafted or budded in situ. Short training courses for growers on orchard management, pruning, propagation, harvesting etc. have been conducted many times each year. The sites of training are at the Royal Project Stations as well as at village level.

4. ESTABLISHMENT OF ORCHARDS

Generally, the deciduous fruit trees are planted in the lands that used to grow opium poppy or field crops like maize and beans, where there is very little land preparation needed. In some villages where the local peach trees existed, top working or frame working with good cultivars of peach or plum has been done. Clearing the forest to plant the deciduous fruit trees is forbidden as it is against the law, which is one of the reasons for the low hectarage of deciduous fruit trees grown in the area of Northern Thailand (Table 2).

As mentioned earlier, almost all kinds of deciduous fruit trees perform well in areas above 1,000 m where opium poppy is produced. Of these, the very steep areas with greater than 30 degree slopes are used for natural forests or for re-forestation work. The plain areas and those with less than 30 degree slopes are considered for planting crops including deciduous fruit trees. In sloping lands, deciduous fruit trees are planted in the terraces that are about 2 m wide. Growers prepare the terraces with assistance from the Land Development Department. Usually, the trees are planted at 4-6 m apart.

In the highland areas of Northern Thailand, a dry spell of about 4-6 months is experienced, and most of the orchards are grown under rainfed conditions. Therefore, the planting season is during the rainy period. The general practice of hill tribe growers is to plant their trees at the beginning of the rainy season, so that the trees can utilize the moisture in the soil for fast establishment.

For planting, some growers dig the planting holes 2-4 weeks before the planting operations begin. This is normally carried out at the beginning of the rainy season. Usually, holes are prepared manually to a size of about 50 × 50 × 50 cm. For refilling the holes, organic material and fertilizers are recommended. The mixture is usually composed of topsoil and well decomposed organic matter in an equal ratio, and this is used to refill the holes after planting.

5. CARE AND MANAGEMENT OF ORCHARDS

The routine operations in caring and management of deciduous fruit orchards are pruning and training. As the weather is rather warm, especially in the day time even in winter months, and the growing period is long and growth is rather vigorous, pruning is essential to keep the tree in good shape to get a satisfactory yield. After planting, the young trees are generally trained into an open center system which is used for stone fruits and persimmon. The training systems for Asian pear and apple are a modified bending system, where all bearing branches are bent horizontally by tying the branches with bamboo poles.

Due to their fast growing habit, deciduous fruit trees are pruned two times a year. The first pruning is done straight after harvest, i.e. summer pruning; this is to get rid of weak and unproductive branches, leaving the new shoots less competition for food. Complete fertilizer of N P K (15: 15: 15) is applied at the rate of 2-5 kg per tree at the beginning of the rainy season. The second pruning or winter pruning is done when the trees are dormant. This is to cut off excessive branches and to shape the trees. The second application of chemical fertilizer is applied during the fruit development stage by repeating the amount and rate of fertilizer applied in the first application. Animal manure or compost is also added to the trees at the rate of 5-10 kg per tree. This application is usually done before the growing season.

Weeding is occasionally done under the tree canopy and due to the long dry period mulching is generally practiced. The weeds taken out are used to make compost. The frequency of weeding depends on the growers and site of orchards; usually it is done once or twice a year.

The majority of deciduous fruit orchards are grown under rainfed conditions. In the areas where there is ample water supply (from creeks or streams) drip irrigation system has been installed in some orchards, but it is costly and sometimes beyond the reach of hill tribe farmers.

The major insect pest affecting deciduous fruits is oriental fruit fly (Dacus dosalis and D. sonatus). The flies lay eggs in the young fruits, and the larvae feed inside the fruit. The damaged fruits drop to the ground and the insects grow into a pupated stage in the soil during winter. When the weather becomes warmer, the adult flies emerge and can start damaging the crops again. The preventive measure to control this insect is to individually bag immature fruits, as well as hanging bottles with insect pheromones such as methyl eugenol, together with an insecticide such as malathion. This is to attract the male flies and destroy them in order to reduce the population. Two common diseases are rust (Tranzchelia pruni-spinosae) and anthracnose (Collectotrichum sp.) which can be controlled by a prophylactic spray of a fungicide before the damage reaches epidemic proportions.

Chemical spraying to control pests and diseases is generally not recommended, as deciduous fruit trees are grown in the watershed areas. The precaution of not using chemicals in the watershed areas is sensible as it helps to protect the environment; also, to prevent contamination of the water supply of people in the lowlands as well. Therefore, biological control together with preventive orchard management techniques are the two key measures adopted in these areas.

6. INTERCROPPING

Deciduous fruit trees are perennial and they usually require 4-5 years to become productive; during the initial stage the farmers have to grow cash crops such as vegetables, cut flowers and others for their livelihood. Research conducted by the Royal Project showed that many kinds of vegetables, flowers and field crops can be successfully grown in these areas. These crops have been introduced to hill tribe growers as an insurance against risk and uncertainty in the highlands. The emphasis is primarily on food security and efficient use of farm resources, although seasonal cash income would be derived from fruit trees. In fact, the integration of deciduous fruit tree species into the land use system in the highland areas is the most preferable agroforestry practice adopted by The Royal Project, as we need hill tribes to stay in one place and develop permanent land use systems, as well as to stop the practice of shifting cultivation.

7. HARVESTING OF FRUITS AND YIELDS

The yield of each deciduous fruit species is given in Tables 1 and 2. The figures are rather low in comparison to those grown in other temperate areas. However, when considering the income that the growers can get from their crops, this seemed to be economically feasible, as their earnings are much higher than what they normally obtained from cultivating opium and other field crops.

There are many reasons behind the low quality fruits and low yields obtained at present from deciduous fruit tree orchards. Apart from the level of technology practiced by hill tribe growers themselves, the cultivars of the fruits grown are also inferior, as the growing areas limit the cultivation to only low-chilling types which, in general, are lower in eating quality than those deciduous fruits found in European and Japanese markets. The long dry period during fruit development of peach, plum and Japanese apricot also contribute to low yield and low fruit quality. The remoteness of areas and difficulties in transportation also hinder the production of high quality fruits.

8. MARKETING

Nothing much can be said about marketing of deciduous fruit in Thailand. All that is produced is locally consumed, and there is no problem in marketing of fresh fruits as there is a ready demand for them. The Royal Project Foundation has established the Marketing Section, which takes the responsibility of selling the fruits for hill tribe growers who derive high returns. These deciduous fruits are sold under the brand name of “Doi Kam” in the market. At present, about 60 percent of the fruits produced in these areas are sold through this channel. The balance 40 percent is sold directly by growers, mostly to tourists visiting the villages.

9. PROCESSING

Under-sized peaches and all Japanese apricot fruits are processed into pickles. They are sold to private factories in Chiang Mai for processing and the products are sold under various brand names. The Royal Project Foundation has 3 canning factories to absorb the excess produce. The project purchases the fruits during peak harvest, so that the prices will not be too low for the hill tribe growers.

10. POTENTIAL FOR DECIDUOUS FRUIT PRODUCTION DEVELOPMENT

At this stage, there is some potential for deciduous fruit growing in the highlands of Thailand. This is due to the increasing demand for these fruits in the country. The reduction in importation of these deciduous fruits in order to save foreign exchange during the economic crisis currently faced by the country has also encouraged their production. The major drawback facing deciduous fruit production development in Thailand is the scarcity of land in the highlands as all the suitable land areas are under governmental control in order to preserve the watershed forest area. The second factor of importance is the unskilled nature of hill tribe growers and the difficulty to train them. This hinders the introduction of modern production technologies into the area.

11. CONSTRAINTS IN DECIDUOUS FRUIT PRODUCTION DEVELOPMENT

The problems facing the development of deciduous fruits in Thailand are briefly outlined as: a) scarcity of land at the altitude of 1,000 m.a.s.l. and above which can provide sufficient chilling hours for the existing cultivars; b) scarcity of suitable species of high quality fruits that can be productive in the area; c) difficulties in educating hill tribe growers; d) people from the lowland are prohibited to venture into the hilly areas and cultivate the land there; and e) insufficient water resources to irrigate the deciduous fruit orchards.

It will take some time before the hill tribe communities can be trained to work with the new technologies. At present, the need to introduce social development measures such as schools, health units, distance learning programs and better communications is being addressed by the Government. These programs also aim to encourage the younger generation to conserve natural resources, protect the environment and produce quality food.

12. GOVERNMENT POLICIES AND PLANS FOR RESEARCH AND DEVELOPMENT ON DECIDUOUS FRUITS

It is difficult to expect the Government to allocate a substantial budget for the development of deciduous fruits in the highlands of Thailand. Reasons attributed to this situation are the financial difficulties currently faced by the country and the fact that the hill tribes, totalling a population of nearly 700,000 people, are treated as a minority with many of them not having Thai citizenship as they move freely across the country’s border. It is therefore questionable and not justifiable to allocate large amount of Government funds earned from legitimate tax payers for hill tribe development.

Until now, almost all of the research work on deciduous fruit trees has been done with financial support from the Royal Project Foundation. Past research on deciduous fruits was done in collaboration and with support from foreign organizations such as USDA, UNDP, FAO, Retired Servicemen of Taiwan, etc. as well as from other private organizations. In the future, more research will be needed, especially on searching for better cultivars as well as better production techniques. The success of the needed research will depend on the support, both financially and morally, that the volunteer researchers from universities, ministries, private sector etc. receive to develop deciduous fruit production in Thailand.

13. CONCLUDING REMARKS

The idea of producing deciduous fruits in the highland areas of Northern Thailand has been initiated by H.M. The King. He established the Royal Project with the objectives of helping hill tribe people in the area to produce enough food or to produce enough income from agricultural crops (in place of opium poppy) in order to achieve a reasonable standard of living. It is quite a difficult task for the Royal Project to pursue the growing concept of watershed management with regard to restoration of natural resource conservation on one hand, and also to satisfy the dietary needs of the hill tribes living in these watershed areas. Besides, the Royal Project also aims to stop the production of opium poppy by growing substitution crops such as deciduous fruits. All combined, these tend to enlarge the scope of highland development in Thailand. Production of deciduous fruits is one of the contributing factors towards this development. Being perennial trees, deciduous fruit crops can substitute or partly substitute the forest trees in restoring the environment and the ecology in the watershed areas. Also, fruits harvested from these deciduous fruit trees can be sold to enhance incomes of hill tribe communities and help to solve the economic problems of these people. Thus, only the sociological problems such as education, welfare, health care, etc. which are directly applicable to hill tribes, await to be solved.

REFERENCES

Kusumo, S. and E.W.M. Verheij. 1991. Malus domestica Borkh. In Plant Resources of South-East Asia (PROSEA). 2. Edible Fruits and Nuts. pp. 200-203. Editors E.W.M. Verheij and R.E. Coronel. Pudoc. Wageningen.

Oyen, L.P.A. 1991. Pyrus pyrifolia (N.L. Burman) Nakai. In Plant Resources of South-East Asia (PROSEA). 2. Edible Fruits and Nuts pp. 272-276. Editors E.W.M. Verheij and R.E. Coronel. Pudoc. Wageningen.

Punsri, P., S. Subhadrabandhu, O. Tuntavirul, N. Tumrongloahapunt and S. Wasee. 1982. Deciduous fruit trees for the highlands. Highland Agricultural Office, Kasetsart University. 48 pp. (in Thai).

Subhadrabandhu, S. 1973. Peach in Thailand. Hort. J. 8: 3 (in Thai).

Subhadrabandhu, S. 1981. A study on some characteristics of peach and nectarine varieties grown on the highlands of Northern Thailand. Kasetsart J. (Nat. Sci.) 15(2):46-53.

Subhadrabandhu, S. 1987. Some characteristics of peach varieties grown in the highlands of Northern Thailand. Acta Horticulturae 199: 83-89.

Subhadrabandhu, S. 1991. Prunus L. In Plant Resources of South-East Asia (PROSEA). 2. Edible Fruits and Nuts pp. 262-266. Editors E.W.M. Verheij and R.E. Coronel Pudoc. Wageningen.

Subhadrabandhu, S., A. Paksasorn, L. Pomphuak and N. Pipattanawong. 1989. Performances of introduced peach and nectarine varieties in Thailand. Kasetsart J. (Nat. Sci.) 23(4): 410-416.

Subhadrabandhu, S. and P. Punsri. 1986. A study on some characters of apple varieties grown on the highland of Northern Thailand. Thai J. Agric. Sci. 19: 141-145.

Subhadrabandhu, S. and P. Punsri. 1987. Deciduous fruit trees as an alternative to opium poppy in Northern Thailand. Acta Horticulturae 199: 39-44.


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