Introduction
The jak (Artocarpus heterophyllus Lam.) is one of the most widely grown fruit crops in the Philippines. It is also one of the most famous in the world because it produces the largest edible fruit that may weigh as much as 50 kg. It is also a unique tree because it is reported to produce fruits below the ground level. Although the jak fruit is very much liked in the tropics, many westerners find its flavour quite peculiar and its aroma too strong.

Primarily grown in the backyard for local consumption, the jak has great export potential and may be developed as an orchard crop. For local consumption, the ripe fruit is usually used for dessert while in some regions in the Philippines, the green fruit is much relished as a vegetable. For export, the ripe pulp may be preserved in syrup or dehydrated. The non-edible portion ('rags') is very rich in pectin and is an ideal material for making jelly.

In 1978, jak ranked fifth among local fruit crops in terms of total area planted and quantity of production. The Philippines has an average area of 13,540 ha planted to jak. With 1,237,200 bearing trees, production is 93,735.1 tons. The jak is grown all over the country but the leading regions in terms of hectarage are Western Visayas (3,456 ha), Bicol (2,000 ha), Central Visayas (1,930 ha), Southern Tagalog (1,910 ha) and Eastern Visayas (984 ha). The other 7 regions have 112-892 ha each planted to jak.

Origin and Distribution
The jak is a native to the rain forests of the Western Ghats of India, but is now widely cultivated throughout the tropical lowlands of both hemispheres. It is an important fruit crop in India, Burma, Sri Lanka, Malaysia, Indonesia, Thailand, the Philippines and many other tropical countries.

The jak was introduced into the Philippines during the pre-historic period. It is now widely distributed throughout the country both cultivated and wild at low and medium elevations.

Taxonomy and Nomenclature
The jak, belongs to the Moraceae, or mulberry family. This family comprises about 55-67 genera and 900-1,000 species of mostly tropical herbs, shrubs, trees and sometimes vines, with 13 genera and about 150 species in the Philippines. The genus Artocarpus Forst. includes 50 or more milky-juiced species of Asiatic tropics and Polynesia with 17-18 species found in the Philippines. India has 18 species. The generic name was derived from the Greek words Artocarpus, meaning 'bread fruit'. The common name 'jak' was given by the Portuguese from the Indian name maka or tsjaka. Jak is known locally as Langka or nangka which is of Malayan origin. It is also called badak in Cagayan and saga kat in the Mt. Province.

The genus Artocarpus also contains other species bearing edible fruits such as rimas, A. altilis (Park.) Fosb.; kledang, A. lancifolia Roxb.; mandalika, A. rigidus Blume.; kamansi, A. camansi Blanco; and bumihan, A. elasticus Reinw. ex Blume. Corner stated that the right botanical name for chempedak is A. integer (Thunb.) Merr. and that A. champeden refers to a Cochin Chinese species different from chempedak.

The Bureau of Agriculture first introduced chempedak into the Philippines in 1912 from China and then in 1913 from Singapore but both introductions failed. It was again introduced in 1914 or 1915 from Singapore and fruited for the first time in Lamao, Limay, Bataan in 1920. The U.P. College of Agriculture at Los Baños, Laguna, introduced chempedak from Indonesia in 1913 and, again in 1927 from Borneo.

Horticulturally, chempedak closely resembles jak but the former has less latex, its pulp is superior in quality and is easily separated from the core, and it is more resistant to fruitfly. Its fruit, however, is smaller and much more odorous than jak fruit. Corner observed that botanically jak and chempedak differ in 14 characters, namely: (a) shape of the base of the leaf lamina, (b) colour of fresh leaf, (c) size of male inflorescence, (d) presence or absence of annulus at the base of the inflorescence head, (e) size of male flower, (f) shape of style apex, (g) adherence of wall and core of ripe syncarp, (h) texture and shape of fruiting perianth, (i) structure of fruiting pericarp, (j) size and attachment of style in the fruit, (k) attachment and shape of seed, (1) structure of testa, (m) dissimilarity of cotyledons, and (n) position of radicle.

The jak is also botanically related to fig, Ficus carica Linn.; mulberry, Morus alba Linn.; chesang, Cudrania tricuspidata Bu.; and yaruma, Cecropia palmata Ww.

Botanical Description
Several authors have described the jak plant and its parts. It is a small to medium-sized, evergreen tree that reaches 8-15 m high. It has a straight, cylindrical, low-branched trunk that measures 30 - 100 cm in diameter and a dense, irregular or spreading crown. The thick greyish-brown bark exudes a viscid and milky sap when injured. The leaves are alternate, spirally arranged, petioled, stiff and leathery, elliptic oblong or obovate in shape, broadest near the tip, with pointed apex and base, entire or three-lobed in the juvenile stage, and measure 10-15 cm long and 5-10 cm wide. They are dark green, and shiny above and pale green and glabrous beneath. The petioles are hairy and 2-4 cm long. The young leaves are pale yellowish-green.

The jak is a monoecious species and the male and female inflorescences or spikes are in separate parts of the plant. The female spikes are solitary or in pairs on special leafy shoots (footstalks) that grow out of the trunk and large branches or occasionally from exposed roots of old trees. They are larger, 5-15 cm long, cylindrical or oblong, dark green, with a stout annulus, 3.0 - 4.5 cm wide at base and embraced by spathaceous, deciduous, stipular sheaths, 5-8 cm long. The peduncles are stout and 8 - 9 mm wide. The female flower is tubular, cohering except at base and apex, the apical part projecting as a 3 - to 7-gorous, blunt or acute cone or pyramid traversed by the style. The style has projecting apex, spathulate or ligulate, and slightly curved. The stigma is clavate. The male spikes are deciduous, much more numerous, densely crowded, cylindric or clavate, 3 - 7 cm long, 2.5 cm in annulus, 1.5 - 2.5 mm broad, at base. The peduncle is stout, 1.5 - 5 cm long and 4 - 5 mm wide. The male flower is fragrant and its tubular perianth is 1.0 - 1.5 mm long and slightly hairy. The single stamen is 1.5 - 2.0 mm high with a broad filament and short anther.

The fruit, technically called a syncarp, is very large, 25-60 cm long, 25 - 50 cm in diameter and may weigh 35 - 50 kg, oblong ellipsoid to pyriform in shape, and covered with short, pyramidal spines. This multiple fruit consists of a greatly enlarged fleshy receptacle and numerous carpels which have fused together, with the interior covered by a thick rind. The pericarp and the pulp around the large seeds are the edible portions. The pulp is thick, rich yellow, sweet and very aromatic. The seeds are numerous, with more or less unequal cotyledons, and vary in size from 2.5 - 4.0 cm long and 1.1 - 2.3 cm wide. The testa is thin and coriaceous.

Varieties
Partly because the jak seedlings bear fruits earlier than seedlings of other fruit trees and that the jak itself is quite difficult to propagate asexually, the most common method of propagation is by seeds. However, because this species is open-pollinated, there is considerable variability in shape, size, quality and other fruit characters among seedling progenies. The pulp character may range from sweet, juicy and aromatic to nearly dry and acidulous.

In India, the jak forms are grouped into 2 based on pulp characters: (a) soft and melting pulp and (b) hard and crisp pulp. Six varieties with soft and melting pulp and two varieties with hard and crisp pulp have been described. In South India, the popular varieties include 'Kapa' with sweet, crisp pulp and 'Barka' with thin, mucilaginous, sour pulp. A promising precocious jak variety, 'Mutton Varikkha' has also been described and is being propagated as a clonal variety by marcotting and inarching. In India and Sri Lanka, the 'Singapore' jak has been introduced. This is an early-maturing variety that bears fruits in about 18 months in the plains and 24 months in the hills. In addition, the fruits generally mature in large number during the off season. Thus, by planting this variety and the ordinary type, it is possible to harvest fruits nearly all year round.

In the Philippines, there are also numerous seedling trees which show distinct variations and three forms have been observed at Los Baños, Laguna. On the whole, however, not many studies have been done on varietal improvement and on the description of varieties. In Thailand and Malaysia, selection for outstanding jak trees has been made and the outstanding trees have been propagated asexually.

In Malaysia, and even in the Philippines, some jak trees have been reported, although very rarely, to bear fruits on their roots. These fruits developed on adventitious root suckers. They developed underground and as they increased in size they raised small mounds which they eventually burst, thus disclosing themselves. However, no botanist has ever seen such a tree to verify the reports.

In the Philippines, the production of plants bearing jak characters from seeds of a chempedak tree has been reported. This provides evidence of the existence of natural hybridization between the two species and this is considered a hindrance to rapid propagation of chempedak and popularization of its culture. Obviously, to maintain the chempedak characters, outstanding chempedak trees should be propagated asexually.

Soil and Climatic Adaptations
The jak thrives best in moist tropical climates below an elevation of 1000 m in areas with well-distributed rainfall. It is probably the most cold-tolerant species in the genus, as trees have produced fruits in southern Florida, although they have been at times seriously injured by frosts. In the Philippines, it grows well on all climatic types although a warm, wet surrounding is best.

The tree grows well on almost any type of soil. But for best performance it prefers a deep, well-drained, sandy or clay loam soils. While the soil moisture must be kept always at a high level, the tree cannot tolerate water stagnation and ill drainage.

Nursery Practices

Seed Preparation and Germination
The seeds for planting should be obtained from outstanding mother trees. A fruit may contain 100 - 500 seeds, majority of which weigh 3.6 g each. There is no apparent correlation between fruit size and seed number. After extraction from the fruit, the outer covering (perianth lobes) of the seeds is removed as this lowers seed germination; the seeds are thoroughly washed in water to remove all the slimy material. Only large seeds from a fruit should be selected for planting, because studies conducted in India have shown that large, heavy seeds have higher germination, retain their viability longer, sprout earlier and produce healthier seedlings than small, light seeds.

The jak seeds do not remain viable for a long period when exposed to the elements and should be sown immediately after extraction from the fruit. Germination tests conducted in India have shown that seeds may remain viable for one full month even under ordinary storage conditions, but germination percentage decreases somewhat and sprouting time increases with lateness of sowing. For example, fresh seeds germinate in 32 days while month-old seeds germinate in 45 days. Thus, it is still advisable to use fresh seeds. If the seeds cannot be sown right away, they should be placed in moist coir dust, sawdust or sphagnum moss. In any case, the cotyledons should not be allowed to dry and shrivel as this will cause the seeds not to germinate.

In studies conducted in India, soaking the seeds in water 24 hours prior to sowing has been observed to increase sprouting and to reduce germination time. It has also been observed that the germination percentage of the jak seeds soaked in NAA solution for 24 hours, the seedling height and leaf number, decrease with increasing NAA concentrations from 25 - 200 ppm. Percent seed germination and seedling height at 25 and 50 ppm NAA and leaf number at 25 ppm NAA were better than in the control. Soaking seeds in 25 ppm NAA for 24 hours prior to sowing was therefore recommended. In another study, it was found that seeds soaked in 100 - 500 ppm GA solution for 24 hours gave 100 percent germination. Seeds treated with 500 ppm GA produced twin seedlings. The other growth regulators had no marked effect on seed germination. Chlorophenoxyacetic acid (CPA) caused splitting of cotyledons and thus, damaged the seeds.

Jak seedlings have a long taproot system which is very sensitive to injury and thus, do not withstand transplanting well. For this reason, it is advisable to sow the seeds in individual containers or directly in situ. If seeds are to be started first in seedbeds, the seedlings should be transferred to individual containers before the food reserve in the cotyledons is exhausted. Otherwise, there is a poor chance that they will recover from the shock of transplanting. In coffee plantations in India where jak is used as a shade tree, jak seeds are sown directly in the field. Three seeds are planted at the centre of the hole. Later, the 2 weaker seedlings are removed, leaving only the healthy and straight one to develop.

The seeds germinate earlier if they are sown either horizontally or with their embryos pointing downward. On the average, seeds germinate in about 18 days although germination occurs over a period of 2 months. Jak seeds are usually monoembryonic although rare cases of seeds producing 2 or more seedlings have been reported.

Care of Seedlings
Growth of jak seedlings is rather slow during the first year. Plants increase in height by about 2 - 3 cm per month and new leaves take about 12 days to fully expand to normal size. For more rapid growth, they may be planted in clay loam soil mixed with compost or other source of organic matter and should be watered regularly. They may be fertilized every 2-3 months with a small amount of nitrogen-containing fertilizer. Seedling growth may be accelerated by spraying them with 25 - 100 ppm GA. Although they can tolerate full exposure to sunlight, they should be placed in a partially shaded area.

Propagation
The jak is commonly grown from seeds, although vegetative methods of propagation have been tried with varying degrees of success. In many countries, propagation by seeds is still the cheapest, easiest and most convenient method available. However, plants grown from seeds exhibit a high degree of variability so that different forms and qualities of fruits exist. For this reason, superior trees should be propagated asexually.

The jak may be propagated asexually by marcotting, inarching, budding and grafting. The earliest marcotting trial in the Philippines has shown that branches that are 3.0 - 4.5 cm in diameter produce roots in 171 days. Another local study has shown that branches form callus within 23 - 26 days and produce roots within 98 - 111 days. In india, a marcotting trial using 10-year-old branches 1.4 - 1.8 cm in diameter has shown greater rooting and survival of marcots using NAA. Rooting is more profuse in marcots treated with 0.025 percent NAA solution which may be responsible for greater survival.

Marcots are ready for transplanting in 3 months. In another trial in India using different growth regulators, 1 percent IBA has been found to be the most effective in marcotting branches 1.0 - 1.5 cm in diameter. Such treatment produces 100 percent success, induces the branches to root in only 22 days, and gives more and longer roots. Similar favourable results have been obtained when IBA is applied in combination with either NAA or IAA. The fact that IAA-NAA mixture has not produced favourable response suggests that only the IBA in the mixture causes the response. Greater response is obtained when marcotting is done during the rainy season. While marcotting appears to be an effective method of propagation and gives a relatively high success, the problem of establishing newly-marcotted plants makes this method not easily accepted for widespread use.

Inarching, like marcotting is suitable for small scale jak propagation. Its advantage over marcotting is that establishing inarches is not a problem. In India, inarching has been found 84 percent successful using jak seedlings as rootstocks. This method is also practiced to a large extent in Thailand. In the Philippines, interspecific graft-compatibility studies have shown that jak seedlings can be used successfully as rootstocks for inarching rimas and chempedak.

Patch budding is the method commercially used in propagating jak in Malaysia. In India, patch budding has given the best results of the different budding techniques tried. This method gives very high success in May to June (as high as 100 percent success in June), because during these months both the scions and stocks are in active stage of growth. In Sri Lanka, budding by the modified Forkert method using jak seedlings as rootstocks budwoods from previous season's growth is practiced. In the Philippines, chempedak has been successfully shield budded on jak seedlings.

Budding, it appears, may be done any time of the year as long as the stocks are kept in active growth. Best rootstocks are 8 to 11 month-old chempedak seedlings although jak and mandalika seedlings may also be used.

Although there is no published report on grafting jak, this method is nevertheless used to a limited extent in the Philippines. At the Bureau of Plant Industry's Mandaue (Cebu) Experiment Station, cleft grafting is used. There is a need, it appears, to cure the budstick and rootstock before cleft grafting is done. One-year-old, brown budsticks are collected and buried in an inverted position in moist sand or soil a day before grafting. The rootstock is headed back a day before. This practice, it is claimed, reduces the amount of latex in the parts of the stock and scion that will be joined and increases the chance of success.

All cuttings failed to root in studies on propagating jak by stem cuttings in the Philippines. Similar results have been obtained in India despite treating the cuttings with hormones.

Cultural Practices

Land Preparation
Before the planting materials are set in the field, the land intended for planting should be prepared in some way. For backyard planting, land preparation is very simple and consists of digging holes large enough to accommodate the ball of soil that goes with the planting materials. If the land is covered with second-growth forests, the trees should be cut down and the stumps removed or burned. No additional land preparation is necessary. For medium to large scale planting in the open, the soil should be plowed and harrowed several times until the desired soil tilth is attained. The land should be prepared before the onset of the rainy season to thoroughly expose the soil before planting.

Planting
As stated earlier, the jak seedlings are very sensitive to root injury during transplanting. During seedling development in the nursery, the primary root should not be allowed to penetrate through the container and to establish itself in the soil. If this happens the root will have to be cut during transplanting in the field. This would result in additional injury to the plant and would further slow down its recovery. To minimize this problem, the seedlings should not be allowed to grow too big in the nursery. They should be planted in the field when they are about 1 year old or younger.

During transplanting, great care should also be observed in removing the plants from the containers so as not to injure the roots and disturb the soil in which the roots are growing. If polybags are used as containers. the problem could be minimized by cutting only the bottom of the container. The plants are carefully set in the previously prepared holes which are later filled up with topsoil mixed with compost. The soil is pressed down around the base of the plant to remove large air spaces.

The leaves should be pruned in halves and the extra shoots cut to reduce transpiration. Pruning may be done while the seedlings are still in the nursery or before the plants are set in the holes. In India, the stem of the newly-transplanted seedling is wrapped with banana sheath to protect it from sunscalding.