The Philippines is an archipelago of 7100 islands and islets in the Pacific (Zaide 1983). It has a total land area of 297 409 km2 , and a coastline that is 17 360 km long. A tropical country, it is located at latitudes 5o -20o N of the equator, and longitudes 117o -127o E (Britannica Atlas 1969).
Several fruit trees that bear edible nuts are claimed to have their centre of diversity in the Philippines. The most important of these is the pili species (Canarium ovatum Engl.), whose geographic distribution in the country remains limited to areas located relatively close to its centre of origin. For this reason, the present production of the plant is confined to a limited area of the Philippines.
The pili nut has several botanical relatives in the Philippines, as well as in other tropical countries, which could be used as rootstocks in vegetative propagation. These allied species could also be used as parents in hybridization, to improve the productivity of the cultivated pili nut. Furthermore, owing to the high degree of open-pollination which naturally occurs, pili nut trees grown from seeds exhibit a wide range of variability in many important horticultural characters. It has therefore not been necessary to apply artificial hybridization to this species, as desirable genotypes can be selected from the existing genepool.
Because of its economic uses, the pili nut is a highly appreciated species. Its existing genepool might not seem to be under any immediate threat, but in fact, the total pili tree population is being rapidly reduced. Although the pili tree is known to be one of the most typhoon-resistant species, a number of trees are destroyed by the devastating typhoons that hit the area of pili cultivation each year.
The greatest threat to the genetic diversity of the species, however, is posed by humans. During periods of food insecurity, such as after a major typhoon, the local population is known to cut down pili trees and sell them as lumber or fuelwood. There is therefore an urgent need for collecting missions, to conserve the remaining diversity of the pili nut genepool.
Fortunately, vegetative propagation occurs in the species, which allows trees with useful traits to be conserved exactly as they are. There is a need to continue planting seedlings, however, to ensure that genetic variability in the species is continually increased.
Taxonomy and nomenclature:
Canarium ovatum Engl. (in A. DC., Monogr. Phan. 4 (1883) 110) belongs to the family Burseraceae. This family consists of 16 genera and about 550 species in the tropical regions of both hemispheres (Leenhouts 1956). In the Philippines, the family is represented by five genera, namely Canarium, Dacryodes, Garuga, Protium and Santiria.
The genus Canarium (derived from the Malay name ‘kanari’, the local name for one of the species), contains about 75 species of trees which are mainly found in tropical Asia and the Pacific, and a few species in tropical Africa (Leenhouts 1956). About 53 species were believed to be found in the Philippines (Merrill 1923), but much later, the number was reduced to nine species (Leenhouts 1956). The known Canarium species and their distribution are listed in Appendix I. The distribution of the Canarium species of the Malaysian region is shown in Fig. 1.
At present, at least four species are of economic importance. Canarium ovatum (known locally as ‘pili’ and ‘pilaui’) is the most important nut-producing species in the Philippines. Canarium indicum is an important nut-producing species in the Solomon Islands (locally called ‘ngali’), Papua New Guinea (locally called ‘galip’) and Vanuatu (where it is known as ‘nangai’) (Evans 1993). Canarium album, known in English as Chinese olive, ‘samo cheen’ in Thailand and ‘tram trang’ in Vietnam, is important in these countries for its edible pulp and kernel (Verheij and Coronel 1991).
Canarium luzonicum, most commonly known in the Philippines as ‘pisa’ and ‘basiad’, is important, not as an edible nut but for its oily resin (known locally as ‘sahing’), which is tapped from the trunk (Fig. 2). When processed, it is called ‘brea blanca’ (white pitch) and is exported as Manila elemi (Manalo and West 1940; Brown 1954; Coronel 1983).
The remaining Canarium species are little understood agronomically, although these minor species may in the future prove useful as rootstocks in clonal propagation, or as parents in hybridization of the cultivated species.
The pili is an erect to spreading, deciduous, predominantly dioecious, medium-sized to large tree that may reach a height of 30 m or more. Very old trees can have a trunk diameter of more than 50 cm (Fig. 3). The leaves have persistent deltoid to lingulate stipules, are spirally arranged, imparipinnate and about 40 cm long. The leaflets are ovate to elliptic, 4-24 cm long and 2-12 cm wide, stiff-coriaceous, entire, base oblique, rounded to subcordate, apex abruptly acuminate and with 8-12 pairs of nerves.
The flowers are borne on cymose inflorescences at the leaf axils of the young shoots. The inflorescence on female trees is about 7 cm long and has 3-6 flowers (Fig. 4a), while that on male trees is ~10 cm long and has an average of 18 flowers (Fig. 4b). In the female flower, the calyx is saccate, gamosepalous, about 1.5 cm long, 1 cm wide, and has three thick, light green sepals. The three greenish-yellow petals are about 2 cm long and 1 cm wide.
The six non-functional stamens arise from the base of the disk. The pistil is about 7 mm long and consists of a functional superior ovary, a simple style about 1.5 mm long and a three-lobed stigma. The ovary has three locules, each with two ovules but normally only one of the six ovules is able to develop a seed. In the male flower, the calyx is also saccate, 6 mm long and 4 mm wide, and is composed of three green sepals, tinged with yellow orange at the tips.
The three oblong, inwardly concave, greenish petals are about 10 mm long and 5 mm wide. The pistil is greatly reduced in size and the six functional stamens are also attached to the base of the vestigial ovary. In a small number of male trees, the few hermaphrodite flowers are similar in all respects to the male flowers, except that the former have functional pistils. Such trees are capable of producing fruits, although these are much smaller than those from the females trees.
The fruit, commonly referred to as a nut, but botanically a drupe, is ovoid to ellipsoid, 4-7 cm long, 2.3-3.8 cm in diameter and weighs 15.7-45.7 g (Fig. 5). The pulp is composed of a thin skin (exocarp), which is smooth and shiny, and turns from light green to purple or nearly black when the fruit ripens, and a fibrous, thick flesh (meso- carp).
The shell (endocarp) is carpellary in origin. Its inner layer arises from the innermost epidermal cells surrounding the loculi, while its outer layer develops from the numerous hypodermal cells. The shell is elongated and trigonous, and is nearly triangular in transverse section, with its corners rounded and one of its sides wider than the others. The basal end of the shell is pointed, while the apical end is more or less blunt or obtuse.
It is tawny to nearly dirty brown outside, and more or less brown, shiny and glabrous inside. On the broad side of the shell, which is often concave or elevated, is the functional locule, containing the mature seed, which also has distinct grooves on the outside that indicate the place where the shell breaks when the seed germinates. The seed is made up of a brown, papery seedcoat surrounding the embryo, which has two white cotyledons. The kernel weighs 0.74-5.13 g and constitutes 4.4-16.6% of the whole fresh fruit.
The pili is a dioecious species with gametic chromosome number n=23 (Villegas and Coronel 1979). The order of blooming is basipetal, i.e. the oldest flower and the first to open is at the tip of the inflorescence and blossoming proceeds downward (Linsangan et al. 1979).
Anthesis of both male and female flowers takes place between 4 pm and 6 pm. Anther dehiscence and stigma receptivity take place at anthesis, or immediately afterwards. At anthesis, the flowers emit a fragrant odour, suggesting that the pili flowers are basically insect-pollinated. The anther changes in colour from white to yellowish at dehiscence and turns brown in the morning of the following day.
At the time of receptivity, at anthesis, the stigma is yellowish and sticky, and begins to turn brown the following morning. Fruit set in flowers pollinated at anthesis was recorded at 87.5% (Linsangan et al. 1979). Flowers pollinated 24 hours after anthesis failed to set any fruits. From pollination, the fruit was found to take about 10 months to reach maturity (Linsangan et al. 1979) and another 2 months to reach full ripening (del Rosario 1984). Ripe pili fruits are believed to be eaten by hornbills, who expel the nuts, dispersing them over a considerable distance.
Monkeys also gather the ripe fruits, eat the pulp and throw away the nuts, contributing to their dispersal in the process. Wild pigs, wild deer and rodents consume the pili pulp of the fallen ripe fruits, leaving the nuts behind. Humans gather the fallen fruits and seeds, and may thus be considered a constraint to the successful dispersal of the species, significantly reducing the natural stand of pili nut seedlings in communities and forests.
Origin and geographic distribution:
The pili is indigenous to the Philippines (Merrill 1912, 1923; Wester 1921; Brown 1954; Li 1970). The crop’s centre of genetic diversity is the Bicol region (Fig. 6), possibly in the virgin rainforests surrounding Mt. Bulusan, in the Province of Sorsogon. In the forests of this province, very old pili nut trees measuring more than 50 m in height can still be found today.
The trees have spread northward to the other three provinces (Albay, Camarines Sur, Camarines Norte) of the region located on the island of Luzon. Old pili trees can still be found in these provinces (Fig. 6). The trees have spread further to the island provinces of Catanduanes in the north and Masbate, in the Bicol region. The trees have also spread out of the Bicol region, to the Province of Quezon in the Southern Tagalog region.
It is only in the present century, however, that the pili nut has been dispersed much more widely. For example, seeds were brought from Oas, Albay to Los Baños, Laguna in 1919, and planted along a road now known as Pili Drive, at the University of the Philippines at Los Baños. Seeds were brought to La Carlota City in the province of Negros Occidental, in the Central Visayas region. Residents of the Bicol region, who either worked in or moved to other parts of the Philippines, took pili seeds with them for planting.
The first students at the University of the Philippines College of Agriculture, in Los Baños, took pili seeds home with them for planting, and the pili trees lining Pili Avenue on the campus of Aklan State College of Agriculture in Banga, Aklan (Central Visayas region) were grown from seeds obtained from Los Baños. A municipality in the province of Camarines Sur is named Pili, after the popular nut-producing tree.
Canarium ovatum has not spread much to other countries; even the world-famous botanic gardens in Indonesia and Singapore do not possess living specimens. There are two reasons why this may be so. Historically, there has not been great interest in the pili nut, owing to its thick shell and small kernel. Furthermore, other countries have their own important species. For example, some countries in the South Pacific are growing C.
indicum (Bourke 1994; Evans 1993). The Hawaiian Islands are the remotest location from the pili nut’s centre of origin, where the species is distributed, and some fruit-bearing pili trees can be found at the University of Hawaii Experimental Station at Hilo, on the big island of Hawaii. Other Canarium species are found in the Bicol region (Merrill 1923). These include C. asperum (known in the region as ‘pili-pili’), C. gracile (known as ‘pilingokai’), C. luzonicum (known as ‘malapili’), C. euryphyllum, and C. hirsutum (known as ‘hagushus’). Because of their small nuts, none of these species has economic potential.
Brief history of cultivation:
It is not known precisely when the pili nut was first cultivated in the Philippines, although it must have been in ancient times, when the native inhabitants of the archipelago started gathering pili fruits in the wild. These early inhabitants of the Philippines learned that, as well as the kernel, the boiled ripe pulp was edible. Later, people dug out pili seedlings in the forest, and planted them near their dwellings.
The more resourceful individuals also planted some of the seeds (particularly the large nuts) that they had gathered in the forest. Thus, the process of domesticating and cultivating the pili nut is thought to have begun. Visitors from neighbouring provinces were impressed by the tastiness of the pili kernels, and began taking pili seedlings home for planting. Some of them also grew seedlings from the nuts they brought back. In the same manner, local residents who moved to other provinces took pili seedlings or nuts with them for planting.
Despite its long history of cultivation, the pili has remained a home garden tree and a minor source of income for some people. It is only recently that the pili has been designated a priority crop in the Bicol region. Massive production of planting materials is underway, and it is hoped that in the near future, the pili nut will be grown as a commercial crop and will be ranked with the cashew and the macadamia in the world market.
Measurements were taken from a total of 84 female trees, and the ripe pili fruit was found to weigh from 15.7 to 45.7 g (Coronel and Zuño 1980b). The pili pulp, which makes up about 64.5% of the fruit by weight, contains 73% moisture. On a dry weight basis (per 100 g), it contains: 8% protein, 33.6% fats, 3.4% crude fibre, 9.2% ash, 45.8% carbohydrates and 2.2 kJ (Marañon et al. 1954). The pulp oil, which is clear and greenish yellow in colour, has the following composition: 56.7% oleic glycerides, 13.5% linoleic glycerides and 29.3% saturated fatty acids.
The kernel, which weighs 0.74-5.13 g and which comprises 4.4-16.6% of the whole fruit by weight, contains: 35.6-51.4% moisture, 11.5-15.7% protein, 69.2-76.6% fats and 2.59-4.32% carbohydrates. Its food energy was reported to be 2.7 kJ/100 g, with the following mineral and vitamin contents (per 100 g): 119 mg calcium, 508 mg phosphorus, 2.6 mg iron, 489 mg potassium, 45 IU vitamin A, 0.95 mg thiamine, 0.12 mg riboflavin, 0.4 mg niacin and traces of vitamin C (Intengan et al. 1968). Other authors have reported on the chemical composition of the pili kernel (Brill and Agcaoili 1915; Padilla and Soliven 1933; Garcia 1941).
In comparison, 20-30% of seed kernel of the cashew, a more popular tropical nut than the pili, is edible. The kernel contains 7.6-16.0% moisture, 18.0-25.4% protein, 43.4-57.4% fats and 19.2-21.0% carbohydrates (Coronel 1983; Verheij and Coronel 1991). The pili kernel therefore contains more oil and less protein and carbohydrates than the cashew kernel.
The kernel oil is composed almost entirely of the gylcerides of oleic (59.6%) and palmitic (38.2%) acids. The oil is light yellow, has an agreeable odour and taste, is suitable for culinary purposes and keeps perfectly for as long as 6 months (West and Balce 1923). The pili shell has 3.2% moisture content, 11.9% volatile combustible matter, 11.1% ash and 77% fixed carbon.
The pili is a plant with various uses (West and Brown 1920; Gonzalez and Bunoan 1947; Brown 1954; Galang 1955; Coronel 1966; Lanuza 1969-70). It makes an excellent avenue and border tree, and a verdant shade tree for lawns. Its remarkable resistance to strong winds makes it a good living windbreak for other crops such as bananas and papayas. The pili is also suitable for agroforestry. The young shoot is edible and can be used in cooking and in making green salads. The resin-rich wood makes an excellent firewood, and the wood of other local Canarium species may be used for house-framing and for making boxes, crates and musical instruments (Tesoro and Aday 1990).
The resin or elemi, particularly from C. luzonicum, is tapped from the trunk (Fig. 2) and exported under the name ‘Manila elemi’ (Manalo and West 1940). In pharmacy, elemi is used as an ingredient in plasters and ointments. In industry, it is a valuable raw material in the manufacture of adhesives, printing inks, fireproof and waterproof materials, paints, varnishes, etc. Elemi is also used in engraving and lithography.
Economically, the pili nut kernel is the most important part of the fruit and has many uses (West and Balce 1923; Garcia 1941; Brown 1954; Galang 1955; Oñate 1967). When eaten raw, it is crispy and has a delicious flavour. It is also eaten roasted, fried or sugar-coated. It is frequently used as an ingredient in cakes, puddings and ice cream, and when cooked in syrup, makes a good preserve. The roasted kernel is sometimes used in chocolate-making. It is also rich in oil, which is suitable for culinary purposes. At present, extraction of the oil from the pili kernel is not being explored owing to an inadequate supply of nuts, even for the kernel industry.
The green pulp can be made into pickle, which is best done soon after the shell has hardened, but before the pulp becomes too fibrous (Mercado 1942). The boiled ripe pulp is edible and is usually eaten seasoned with salt, pepper, or with a salted fish sauce (Wester 1915; Garcia 1941; Brown 1954; Galang 1955; Coronel 1966). It resembles boiled sweet potato in texture, but has a rather insipid taste.
It can also be made into a spread (Dipad 1979). No data are available regarding the quantity of pulp consumed as a foodstuff. The pulp also contains an oil that is used for cooking and lighting (West and Brown 1920; West and Balce 1923; Garcia 1941; Gonzalez and Bunoan 1947; Brown 1954). Oil from the pili pulp could also be used in the manufacture of soap and other products, although these potential industrial uses have not yet been exploited.
The hard, stony shell of the pili seed is chiefly used in cooking, for which it makes an excellent fuel (Gonzalez and Bunoan 1947; Lanuza 1969-70). It is also well suited as a component of the growing medium for orchids and anthuriums (Coronel 1983). When polished and varnished, the shell makes an attractive keyholder, and ornaments fashioned out of the shells of other Canarium species are popular with local and foreign tourists in Indonesia (Gonzalez and Bunoan 1947; Coronel 1966).
The use of the pili shell in the manufacture of charcoal has not yet been explored (Coronel 1983). The same is true of the testa or seedcoat of the pili kernel, although when its chemical composition is determined, some industrial uses may be found for this part of the fruit (Coronel 1983). No data exist on local consumption of the different raw and processed products, or on what percentages of the nuts produced go into the processing industry. No exports have been recorded in recent years, and the most recent export figure available is that for 1977, when 3790 kg of various pili nut products were sold to Australia and Guam (Coronel 1983).
A number of processed pili products are currently available in local markets. Pili candies are prepared from whole or halved kernels, which are coated with a glaze of brown (unrefined) or white (refined) sugar, cooled, placed in plastic bags or jars, and sealed. Pili ‘turron’ is made from a mixture of ground pili kernel, sweet potato and sugar, which is flavoured with sesame and vanilla.
The mixture is cooked until it reaches a desired consistency, cooled, cut into uniform pieces and wrapped in plastic. Pili pudding, the last of these products, is made from a mixture of mashed sweet potato, ground pili kernel, condensed milk, butter, sugar and eggs. The mixture, flavoured with vanilla, is poured into small rectangular paper trays and is baked in a moderately hot oven, until it turns a light brown colour.
Range of diversity in major plant characters:
The pili is a highly variable species. Numerous observations have confirmed that seedling trees possess high variability in many important botanical and horticultural characters (Table 1). The first investigation to study the genetic variability of pili seedling trees was conducted at the campus of the University of the Philippines, College of Agriculture in Los Baños, Laguna (Gonzalez and Bunoan 1947).
The trees were found to differ in their sex; almost half of the trees evaluated were male and the rest were female, confirming its dioecious nature. The same ratio of male and female trees was obtained in a later survey (Zuño and Coronel 1982). In a recent collecting trip in Banga, Aklan, the author observed the same ratio of male and female trees in an avenue lined with pili trees.
A low percentage of supposedly male pili trees produced a few hermaphrodite flowers in the inflorescence (Zuño and Coronel 1982). These bisexual flowers were similar in all respects to the male flowers, except that the former had functional ovaries that were capable of developing into mature fruits. The fruits, however, were much smaller than those from female trees. Pollen from the bisexual flowers was also able to pollinate female flowers.
Gonzalez and Bunoan (1947) also observed that some seedling trees had a spreading growth habit; others had more upright branches. Among the female trees, some were prolific while others were less productive. Some were also seasonal in their fruiting, whereas others produced fruits all year round. The latter were later erroneously called ‘everbearing’ pili trees. With regard to other plant characters, pili trees of seedling origin also differ in their precocity, density or profuseness of branching, stem girth of shoots, earliness or lateness of the season of fruit ripening, and length of period of fruit development.
The number of inflorescences/fruit clusters per shoot, number of flowers per inflorescence, and number of fruits set per inflorescence, also differ among seedling trees. The number of fruits set, number of flowers per inflorescence, number of inflorescences per shoot and number of shoots per tree are determinants of the number of fruits produced (or yield) per tree, which also varies among seedling trees.
The stem girth of the shoot is important in asexual propagation. It has been observed that the diameter of pili shoots differs among seedling trees (Coronel et al. 1982). Trees that have smaller shoots would easily match the stem diameter of 1- to 2-year-old seedling rootstocks used in grafting. Variability also exists in the different fruit characters (Gonzalez and Bunoan 1947; Coronel and Zuño 1980b), i.e. nut weight and shape (Fig. 7); pulp weight, thickness, flavour and fibre content; shell thickness; kernel size, colour and flavour.
The length of time taken to soften the pulp when soaked in water also differs among seedling trees, as does the chemical composition of the pulp and kernel. The proportion of saturated and unsaturated fatty acids contained in the oil varies, as does the percentage of filled nuts and the percentage kernel recovery in seedling trees. Leaves from different seedling trees vary in size, number per shoot, petiole length and chemical composition. The nuts from different trees also differ in storage behaviour (i.e. some nuts have longer storage life than others), number of days to germination and percentage germination.
The pili has some 74 relatives, about eight of which are found in the Philippines (Leenhouts 1956). However, not much is known about their usefulness in the improvement of the species. Limited trials carried out in the Philippines showed that seedlings of C. luzonicum can be used as rootstocks in grafting/budding the pili (Wester 1916; Galang and Elayda 1924). The other wild species should be investigated to determine their usefulness in the improvement of pili nut.
An organized approach to the collecting and conservation of pili germplasm was begun when the Institute of Plant Breeding’s National Plant Genetic Resources Laboratory was established in 1976. The range of variability of the pili trees grown on the campus of the University of the Philippines at Los Baños was investigated, as well as that of those at a nearby government research station (Coronel and Zuño 1980b). In Laguna, 84 female seedling trees were evaluated (Table 2).
Several trees of this collection were considered outstanding, in terms of the fruit characters selected, and these were later given variety names (Coronel et al. n.d.). Three of these varieties (‘Katutubo’, ‘Mayon’ and ‘Oas’) were later approved for registration by the National Seed Industry Council, formerly the Philippine Seed Board (PSB 1993). Results of fruit evaluation of the 84 trees in Laguna showed that there were wide variations in fruit and kernel characters among trees (Table 3).
The other fruit characters such as weight and thickness of pulp and kernel also varied greatly among the trees. Proximate analyses of kernel from 17 pili trees showed that the trees also differed in the moisture, fat, protein and starch content of the kernel. Seedling trees respond differently to the different asexual propagation methods such as marcotting, cleft-grafting and patch-budding. Using some of the pili trees at the University of the Philippines, Los Baños, an investigation of the asexual propa- gation methods applicable to the pili was conducted from 1979 to 1981 (Coronel et al. 1972).
It was found that, out of 14 trees used, none was responsive to propagation by stem-cutting. Of 38 trees, 19 responded favourably to marcotting, with a success rate of 10-100%. Among those seedling trees that responded, the number of days to rooting also varied greatly. These findings on marcotting corroborated earlier results (Coronel et al. 1972, n.d.). Out of a total of 21 trees, seven were successfully cleft-grafted, but with a maximum success rate of 25%. Measurements of the shoot diameter of 37 trees ranged from 0.4-2.1 cm, with an average of 1.2 cm. Of a total of 23 trees, 18 were successfully patch-budded, with a success rate of up to 72%.
All the pili nut collections in Laguna are being maintained in the sites where they were originally planted. In addition, the three registered varieties are being maintained as cleft-grafted or patch-budded trees at the Institute’s field genebank. During subsequent collecting missions, pertinent passport and collecting data were obtained for each tree. Each pili tree identified represented one accession.
Ten ripe fruits were randomly gathered from each tree, evaluated individually, and the average calculated for each character. The following measurements were recorded in fresh samples: whole fruit weight, fruit length and diameter, pulp weight and thickness, shell weight and thickness, kernel weight with testa, testa weight and kernel weight. Percent kernel (the kernel as a proportion of the seed) was calculated, based on fresh weight of nut.
Fruit samples from all the pili collections from Bicol and other regions/provinces (Table 2) have been evaluated at least once. The original trees are being maintained in their natural habitats. It was originally planned in 1976 that all the pili accessions would be propagated asexually. This was based on the recommendations contained in the Revised Tropical Fruit Descriptors (IBPGR 1980) that all tropical fruit germplasm collections be conserved in field genebanks as vegetatively propagated trees, genetically identical to the original parent trees.
During the collecting trips, therefore, fruits were gathered only for evaluation, and not to grow seedlings for planting in the genebank. Instead, scions were collected for asexual propagation, but since pili nut scions do not transport well, no asexually propagated plants were produced.
Since 1995, ripe fruits from the original tree collections in Laguna and Bicol, which have been maintained in their natural habitats, have been gathered, and seedlings representing these collections have been planted in the field genebank at the University of the Philippines, Los Baños. In the field genebank in Los Baños, each pili accession is represented by 3-4 grafted or budded plants. In the case of sexual propagation, each accession contains 10 seedlings.
Erosion of genetic resources:
The pili is now a partly cultivated crop, although many people have not fully understood its long-term potential. Much valuable genetic material may have been lost already, but the species does not seem to be in any danger of extinction. Many natural factors have ensured the continuous regeneration and survival of the genetic resources of the pili: its dioecious nature, and the obligatory cross-pollination; its high fruit set; the natural dispersal of nuts by wild birds and other animals; high seed germination percentage, aided by the availability of high moisture during the fruiting season, and tolerance to hostile growing conditions.
However, the statistics indicate that the pili nut tree population has been declining rapidly, principally because of human activity. Local people gather pili nuts for food, significantly reducing the potential number of seedlings that could have sustained the natural population. Seedlings are seldom replanted, and areas that were previously planted with pili trees have been built on. Deforestation also has been caused by trees being deliberately cut down for fuelwood and many other purposes.
While humans currently represent the greatest threat to the preservation of the pili nut genepool, human intervention is also needed to preserve the genetic diversity of the species. A first step in this direction would be a local or national ban on the felling of pili trees. A second step might be to encourage the planting of pili seedlings for reforestation, agroforestation and landscaping. Non-governmental organizations (NGOs) could play an active role in such initiatives.
Thirdly, pili trees (both male and female) that possess important and potentially useful characters should be identified, properly labelled and carefully maintained. These trees should also be propagated asexually, by marcotting, cleft-grafting or patch-budding. Asexually propagated plants from these trees should be planted and maintained in duplicate genebanks, where they could be thoroughly characterized and evaluated.
Varietal improvement of pili nut trees can be achieved by selection of superior trees from existing seedling populations, and by conventional breeding methods, such as hybridization, to further improve existing varieties.
The first method of varietal improvement of the pili is by selection of superior trees from existing seedling populations. This method is presently the most practical, and is likely to be used for some years to come. By virtue of its being a predominantly dioecious species, cross-pollination in nature is the rule in the pili. This has resulted in a great variation among seedling trees and many desirable and useful horticultural characters.
The earliest observations on the existence of different forms in the pili were made by Wester in 1915. On the basis of fruit size, he identified two forms: the short form, with fruits of 4.5-6.0 cm in length, and the long form, with fruits of 5.5- 7.0 cm. Proximate analysis of both forms of the kernel produced similar results (Brill and Agcaoili 1915), although the short form was the one usually sold in the markets.
Wester (1929) also selected the first pili tree that produced thin-shelled nuts, belonging to the long, slender form. The tree bearing these thin-shelled nuts was found in Magkasili, Guinobatan, Albay and was named ‘Albay,’ after the province in which it originated. Wester (1929) also reported another tree with thin-shelled nuts, this time belonging to the short form. The tree bearing these thin-shelled nuts was found in Mauraro, also in Guinobatan, Albay and was named ‘Red’, in honour of its discoverer.
A more systematic evaluation of the species was conducted in Los Baños, Laguna in 1946 (Gonzalez and Bunoan 1947). A total of 95 pili trees, whose seeds came from Oas, Albay and which were planted in 1920, were evaluated for sex expression, productiveness, fruiting season, growth habit, physical and chemical properties of the fruits, and other morphological features. Two trees were selected as outstanding on the basis of their yield and fruit qualities. One of these was later named ‘Katutubo’ (Coronel 1983).
More recent selection work on the pili, conducted in Laguna, the Bicol provinces and other locations, identified 40 promising trees, on the basis of kernel weight (Coronel and Zuño 1980b). Correlation studies of the various pili fruit characters have shown that fruit weight, length and diameter were highly positively correlated with kernel weight (Table 4). Thus, any of these three external fruit characters may be used as a basis for preliminary evaluation or selection of a large number of seedling trees.
In addition to kernel weight, other desirable characters are early bearing, high productivity, short fruiting season, good pulp and kernel qualities, and thin shell (Coronel 1966, 1978a, 1978b, 1983). Several pili varieties have been selected from among the promising seedling trees in Laguna and the Bicol region. The six pili varieties selected in Los Baños, Laguna are briefly described in Table 5 (Coronel et al. 1982). Figures 8a-f show that all the fruits of ‘Katutubo’, ‘Oas’, ‘Mabunga’, ‘Ibalon’ and ‘Isarog’ varieties are oblong, whereas the fruits of `Mayon’ variety are short-oblong.
Box 1. Varietal selection standards for the pili:
- Fruit characters
- Whole fruit (fresh)
- Size: medium to large (at least 25 g)
- Shape: short-oblong to globose
- Nut (dry basis)
- Size: medium to large (at least 10 g)
- Shape: short-oblong to globose
- % filled nuts: at least 90%
- Shell (dry basis)
- Thickness: medium thick to thin (not more than 4.00 mm)
- Kernel (dry basis)
- Size (including testa): medium to large (at least 2.5 g)
- Colour: white
- Shelling recovery: at least 20%
- Tree characters
- Growth habit: spreading
- Vigor: strong
- Branching: profuse with thinner shoots
- Yield: heavy (for 25-year-old tree, at least 5000 fruits per season)
- Reaction to pests and environmental stresses
- Resistance to insect pests: tolerant to resistant
- Resistant to diseases: tolerant to resistant
- Resistance to environmental stress: resistant to typhoons
- Ease of asexual propagation
- Cleft-grafting: high (80-85%)
- Patch-budding: high (70-75%)
Fruit evaluation and tree characterization are continuing for many more seedling trees in order to select better pili varieties. Using the ‘Katutubo’ pili as the check variety, in 1994 the Fruit and Plantation Crops Varietal Improvement Group of the Philippines National Seed Industry Council established a set of varietal selection standards for the pili (Box 1). An outstanding pili tree should be precocious, prolific, with profuse branching, bear large, short-oblong fruits, with thin shell and medium-to-large kernels that ripen over a very short period. It is readily propagated by cleft-grafting and/or patch-budding.
The dioecious nature of the species makes controlled hybridization in the pili a particularly complicated and difficult process, which has not yet been attempted. Like other perennial plant species, a breeding cycle for the pili would require at least 10 years (5-6 years for the seedlings to bear fruits, and another 4 years to evaluate the plant and fruit characters of the new hybrids). While it is easy to determine which trees to use as the female parents, selecting which male trees to use as the male parents is more problematic, especially as the fruit characters of the female trees are selected for, and because these traits are not manifested by the male trees.
The first step in a pili hybridization programme is to establish which male trees possess the desirable characters. This should be done by growing open-pollinated seedlings, obtained from female trees with known desirable characters, such as fecundity, early bearing, large kernel, etc. All the male trees thus produced should be identified and clearly marked as male seedling trees from known female parents.
For example, male seedling trees from the ‘Mabunga’ pili (known for its high yield) can be used as a pollen source for the controlled pollination of the ‘Katutubo’ pili, to develop hybrids that are more prolific than the latter variety.
Table 6 shows that the production areas of the pili are primarily concentrated in the Bicol region, in the provinces of Sorsogon, Albay, Camarines Norte and Camarines Sur (Wester 1915, 1921). In these provinces, the main supply of nuts comes from certain municipalities and districts, which are usually located near mountainous areas (Lanuza 1939; Despi 1965). Production of nuts is mainly from unselected seedling trees.
The Southern Tagalog region (principally the province of Quezon) and the Eastern Visayas region (principally the provinces of Northern and Western Samar) also produce a quantity of pili nuts (Table 6). The other regions of the Philippines either do not produce pili nuts, or their production is negligible. The production figures given in Table 6 are estimated values.
If the yield per tree is calculated, it can be seen that there is a wide variation in production among locations. For example, the yield per tree in the Southern Tagalog region is 0.9 kg in Quezon and 20.5 kg in Oriental Mindoro. In the Bicol region, the yield per tree ranges from 14.0 kg in Albay to 107.7 kg in Camarines Norte. This large discrepancy can be attributed in part to the considerable age range of the bearing trees.
Despite the recent availability of selected varieties, and the development of vegetative propagation methods, the pili is still not planted commercially in the Philippines today. A systematic assessment of the reasons for this is called for. Furthermore, should the economic prospects of the crop be found to be sufficiently good, assistance from the government will be needed to promote the large-scale production of the crop.
The pili does not have strict soil requirements, and is known to thrive on a wide range of soil types and over a wide range of climatic conditions in the Philippines (Coronel 1966; Lanuza 1969-70). At the Paete Land Grant of the University of the Philippines, Los Baños, pili trees grow well, even in very acid soils. For optimum production, however, soils that are deep, fertile and well drained are ideal (Coronel 1966; Lanuza 1969-70).
The pili is a purely tropical species (Chandler 1958). In its native habitat, the Bicol region, the total annual rainfall is about 3300 mm (Table 7). Rainfall is well distributed throughout the year (225 rainy days), although there is more rain from June to January (average 332.6 mm/month) than from February to May (average 167 mm/month). The four regions in Mindanao (Fig. 1) also enjoy well-distributed rainfall and should be able to grow the pili successfully.
The pili also grows well in the province of Laguna, where the total annual rainfall is moderate (1980 mm) and there are distinct dry and wet seasons (January- April and May-December, respectively). There are also several other areas of the Philippines with a similar rainfall pattern, which should be able to grow the pili successfully.
The pili grows well from sea level up to an elevation of 400 m (Coronel 1966; Lanuza 1969-70). It has been reported to grow at much higher elevations in the Cordillera Administrative Region. However, it cannot tolerate the cool period and slight frost of southern Florida (Chandler 1958; Mortensen and Bullard 1964). Temperature and relative humidity in the Philippines remain more or less constant throughout the year, with a mean annual temperature of about 27o C and mean annual relative humidity of about 80%.
The Bicol region is within the typhoon belt and experiences several strong typhoons each year. The pili is known to be extremely resistant to these annual hurricanes. Some people in the region even call the pili the ‘spouse of typhoons’, because of their belief that the stronger the typhoon the pili trees experience, the more fruitful they become. This is related to another belief concerning the harvesting of the pili nuts.
The usual harvesting method is to repeatedly thrash the fruiting branches with a stick, severely defoliating the tree in the process. It is widely believed in the Philippines that this ‘punishment’ encourages the pili tree to produce more flowers and fruits during the next fruiting season. The practice has a scientific basis, however, in that it achieves the correct balance of carbon and nitrogen in the plant.