Abstract
The Southeast Asian region is the center of genetic diversity of numerous edible fruits and nuts which have also benefited the rest of the tropical world. Banana, durian, rambutan, langsat and mangosteen are only a few of the many contributions of Southeast Asia. The region has likewise immensely benefited economically from the introduction of important fruits and nuts from South Asia (e.g. mango, jackfruit), the Pacific and Oceania (e.g. macadamia, breadfruit), tropical America (e.g. pineapple, papaya) and, to a lesser extent, tropical Africa (e.g. miracle fruit). The production of these fruit and nut resources of some 400 species has brought about a vibrant and diverse fruit industry in Southeast Asia.

Introduction

The Southeast Asian region is composed of ten countries, namely Myanmar (formerly Burma), Laos, Thailand, Cambodia, Vietnam, Malaysia, Brunei, Darussalam, Singapore, Philippines and Indonesia. It is located 10^o S to 29^o N of the equator at 90-140 E longitude.

It is the native home of numerous edible fruit and nut bearing plants. Such major fruits as banana, durian, rambutan, langsat and mangosteen are indigenous to Southeast Asia. The region has likewise immensely benefited economically from the introduction of important fruits and nuts from South Asia (e.g. mango, jackfruit, tamarind), the Pacific and Oceania (e.g. breadfruit, macadamia), Latin America (e.g. papaya, pineapple) and, to a lesser extent, tropical Africa (e.g. miracle fruit). The production of these fruit and nut resources of some 400 species has brought about a vibrant and diverse fruit industry in Southeast Asia.

The Southeast Asian region is the major producer and supplier of tropical fruits in the world. This achievement has been brought about by recent advances in fruit production technologies such as development of improved varieties, off-season flower induction, improved postharvest handling practices and better utilization of excess production through processing.

There are still some major constraints to a more productive fruit enterprise. For example, existing fruit varieties are susceptible to major pests and diseases. Biotechnological intervention may speed up solution to this problem. A package of technology that will make feasible high density planting in fruit trees such as mango is still wanting.

This paper discusses the species diversity of fruits and nuts in Southeast Asia, the important economic fruits and varieties that contribute substantially to world fruit supply, specialized production practices, major production problems and possible solutions.

Diversity of Fruits and Nuts in Southeast Asia

Some 400 species of fruits and nuts are grown in Southeast Asia. Ninety percent (or 360 species) are woody plants; the rest are herbaceous species. Banana, papaya and pineapple are herbaceous, edible fruit bearing plants.

Among woody species, 250 are fruit trees, 227 (or 90%) of which are indigenous to Southeast Asia or have been, a long time ago, introduced in the region and are now considered naturalized species. Durian and rambutan are two examples of fruit trees that are indigenous to Southeast Asia, while mango and jackfruit are naturalized fruits from other tropical Asian region.

The tropical countries of Central and South America have also contributed to the diversity of fruit and nut species in Southeast Asia. Herbaceous species like pineapple and papaya and woody species like sapodilla and soursop are important contributions of Latin America to the fruit industry of Southeast Asia.

The Major and Minor Fruits of Southeast Asia

On a regional level, it is not easy to delineate which fruits should be considered major commodities in Southeast Asia because each country apparently uses a different set of criteria for classification. Consequently, a major fruit in one country may be a minor common in another and vice versa. Malaysia, for example apparently adopts a more liberal definition and considers 39 species as major fruits while the Philippines considers only five or so species as major fruits. Other Southeast Asian countries obviously have their own lists of such major fruits.

On the basis of their overall economic importance in the region 11 species may be considered major fruits of Southeast Asia (Table 1). These are, in alphabetical order, banana, durian, jackfruit, langsat, mandarin, mango, mangosteen, papaya, pineapple, pummelo and rambutan.

Based on a five-year average (1995-1999), world production of banana is 57,701,000 tonnes, 16.6% of which is contributed by Southeast Asia (Table 2).

The Philippines (6.2%), Indonesia (5.2%), Thailand (3.0%) and Vietnam (2.2%) are among the world leaders in banana production. World production of pineapple, based on a five-year average (1995-1999), is 12,539,000 tonnes, 31.9% of which is contributed by Southeast Asia (Table 3). Thailand (16.3%), Philippines (12.1%) and Indonesia (3.5%) are among the world leaders in pineapple production.

World production of mango, based on a five-year average (1995-1999) is 23,213,000 tonnes, 12.1% of which is contributed by Southeast Asia (Table 4). Again, Thailand (5.6%), Philippines (3.5%) and Indonesia (3.0%) are among the world leaders in mango production.

The minor fruits of Southeast Asia are those that are sold as fresh or processed products but are grown in limited scale (e.g. in home gardens). Some have the potential to become major fruits if they are fully developed. Table 5 lists some of the minor fruits of Southeast Asia. One tropical American fruit that has recently been introduced in Southeast Asia is the abiu (Pouteria caimito, Sapotaceae). Introduced by the author from Queensland, Australia to the Philippines in 1987, abiu is becoming popular because the tree is smaller, precocious and prolific and the fruit is attractive and of good eating quality.

Fruit Varieties

Table 6 lists the fruit varieties grown in Southeast Asia. There are ample varieties for the major fruits like banana, durian ,jackfruit, mango, pineapple, pummelo and rambutan.

(Ind) Indonesia (Mal) Malaysia (Mya) Myanmar (Phi) Philippines (Tha) Thailand

Most of the fruit varieties are selections from seedling trees. This is true in the case of fruit trees like durian mango and rambutan. The few hybrids include Eksotika (Malaysia) and Sinta (Philippines) papaya.

One reason why some Southeast Asian fruits have remained of minor economic importance is the lack of outstanding varieties for commercial cultivation. The Philippines has partly addressed this problem by organizing the Fruit Crops Technical Working Group on Varietal Improvement under the National Seed Industry Council (formerly the Philippine Seed Board) of the Department of Agriculture. Formed in 1994, the Technical Working Group, chaired by the author, initially established varietal selection standards which subsequently have been used to approve/disapprove applications for registration of new fruit varieties. The new varieties are then endorsed for further scrutiny by the Technical Secretariat, composed of the chairpersons of the 15 or so crop technical working groups. Final approval rests on the Council itself which is chaired by the Secretary of the Department of Agriculture.

Table 6 shows that aside from the major fruits, the Philippines now has registered varieties (marked R) for some minor fruits like abiu, caimito, bignay, bitungol, cashew, marang, sapodilla and soursop. To date, 44 fruit varieties have been registered with the National Seed Industry Council. Scion groves of these fruit varieties are now being established in different geographic regions for wider dissemination of asexual propagules.

With the advent of biotechnology, some Southeast Asian countries have recently embarked on fruit varietal improvement through genetic engineering. The Philippines and Thailand, for example, are hoping to impart ringspot virus resistance to the Solo papaya. The Philippines is also developing Lakatan banana that is resistant to the banana bunchy-top virus, as well as Carabao mango and Solo papaya that have delayed ripening properties.

Propagation

Micropropagation by in vitro culture is well established in Southeast Asia for herbaceous fruits like banana, pineapple, and papaya. In the Philippines and most other countries in the region, however, the use of tissue-cultured propagules is confined mainly to banana, and even in this fruit, only by large plantations. Small banana growers still plant corms or suckers because of lack of tissue-cultured plantlets. Papaya is still grown from seed and pineapple, even in large plantations, is still grown from crowns, slips and suckers.

On-going study at our Institute of Plant Breeding shows that seed pieces of mangosteen can be successfully cultured in vitro. In the case of asexual propagation of fruit trees, there seems to be some country specialization of sort. For example, Thai fruit propagators tend to favor sucker grafting wherein bare-root seedling rootstocks are grafted to the branches to the propagated. Malaysian propagators, on the other hand, are more skilled in propagation by patch budding and other modified techniques. Filipino and Indonesian fruit propagators are more at ease with cleft or wedge grafting.

In the Philippines, the calamondin and the different citrus species, except pummelo, are propagated, not by patch budding or cleft grafting, but by shield budding using as rootstocks seedlings of the so-called calamandarin, believed to be a natural calamondin-mandarin hybrid but is actually the sour Cleopatra mandarin. Pummelo is shield budded on pummelo seedlings.

Unique Orchard Practices

There are orchard management practices that are quite unique to Southeast Asia. Some of these are enumerated below.

1. Flower forcing in mango. In fruit crop production, flower forcing in pineapple is a universal practice using etephon as the flowering agent. In the Philippines, flower forcing in mango used to be accomplished by smudging. In the early 1970s, however, potassium nitrate at 1-3% dosage was found effective in off-season flower forcing of local mango varieties. This technique is now a regular feature of mango production in the country.

   The use of paclobutrazol, a growth retardant, has also been found effective in forcing mango and durian trees to flower.

2. Leaf stripping in apple. This unique practice is done in Indonesia to force apple trees to flower by stripping all the leaves and bending the branches.
3. Fruit production is a no-no in waterlogged areas. In Thailand, fruit growers are successful in utilizing inundated land by painstakingly constructing raised beds and planting different kinds of fruit crops on these beds. They not only have waterways, they also have a ready source of water for irrigation and spraying.
4. Fruit bagging. There is nothing unique in bagging fruits to protect them against pests, notably fruitflies, if the fruits are within reach of the farmer. The practice becomes unique when the tree is several meters high and the farmer has to wrap a thousand fruits a day using only a bamboo pole as his tool. This is a common practice in the Philippines to wrap mango fruits and in Thailand to wrap santol fruits.

In the Philippines, small pineapple growers put a teaspoon of sugar in their mouth during planting so that the fruits would taste sweeter. Superstitious belief?

Major Constraints to Fruit Production

In general, production per unit area (e.g. tonnes/ha) in herbaceous fruits like banana, papaya and pineapple is much higher than in fruit trees like mango and durian. A volume of 35-40 tonnes per ha is easily attainable in banana production, whereas 10-15 tonnes is probably the current average for mango.

The disparity in production is due to their large size in the case of fruit trees and the low yield per unit mass. The size of the tree should therefore be drastically reduced to be able to plant much more trees per unit area. This can be achieved by using a dwarfing rootstock, appropriate training and pruning and judicious application of growth regulating chemicals. Through appropriate cultural management practices, the number and size of fruits per tree could also be increased.

Other major constraints to fruit production include the existence of low-yielding and poor-quality varieties, occurrence of serious pests and diseases that reduce fruit yield and quality and lack of adequate knowledge on the proper nutrition management of fruit crops.

Summary

• Southeast Asia grows some 400 fruit and nuts. Majority are either indigenous or naturalized species. The rest are from other tropical regions such as America and Africa.
• The major fruits are banana, durian, jackfruit, langsat, mandarin, mango, mangosteen, papaya, pineapple, pummelo and rambutan.
• Southeast Asia contributes 16.6%, 31.9% and 12.1% to the world production of banana, pineapple and mango, respectively.
• There are many fruits of minor economic importance, but which with proper development have potential to become major fruits.
• There are outstanding varieties of the major fruits. Many minor fruits lack good varieties and this is one major constraint to their development.
• Micro- and macropropagation techniques are in place for both herbaceous and woody fruit crops.
• There are orchard practices that are unique to Southeast Asia: flower forcing in mango and durian, leaf stripping and stem beading in apple, fruit growing in raised beds and fruit bagging in tall trees.
• Major constraints to better fruit production include lack of production technology for high density planting, low yielding and poor quality varieties, occurrence of devastating pests, and lack of knowledge on nutrition management of fruit crops.

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