Pummelo (Citrus maxima), otherwise spelled pommelo and pomelo and also called in various countries as shaddock, pamplemoussier, jeruk besar, jeruk bali, jambua, limau betawi, limau bali, muli, som-o, ma-o, shouk-ton-oh, suha, lukban, kabugaw and buongon, is a popular fruit crop of the Orient. It has the biggest fruit among the citrus species.
It is closely related, and its world production data is always associated, to the grapefruit (Citrus x paradisi), the only major citrus fruit that originated outside of Southeast Asia. In Southeast Asia pummelo is grown in home gardens, in mixed citrus orchards and in pure pummelo orchards. The Philippines classify it as a high-value cash crop.
For 2008, the top 10 world producers of grapefruit (including pomelos) are USA, China, Mexico, South Africa, India, Argentina, Turkey, Cuba, Brazil and Tunisia ( FAOSTAT , 2010). Data presented by Ganjun (2009) show that China produced 540,546 tons in 60,060 ha, yielding an average of 9 tons per hectare. 90 percent was produced for domestic consumption. There are reports, however, that a single tree can yield 70-100 fruits per year which is equivalent to 20 tons/ha per year (Verheij and Coronel, 1992).
The pomelo plant is a small tree 5-15 m tall, low-branching; spiny if propagated from seed or spineless if propagated vegetatively. Trees grown from seed are usually tall and slender and start bearing fruits 6-8 years after sowing. The fruit is a special type of berry called hesperidium, segmented with large, pale yellow or pink pulp-vesicles, filled with sweetish juice. Seeds are usually few, large, monoembryonic.
The fresh juicy pulp vesicles are eaten off hand or used in the preparation of fruit salads. Sometimes the juice is extracted, and in China it is processed into wine. The white inner part of the peel can be candied or preserved in syrup after removing the outer peel containing oil glands. The flowers are very fragrant and have been used in making perfume. The wood is used for tool handles. The leaves, flowers, fruits and seeds are known for their medicinal applications including the treatment of coughs, fevers and gastric disorders. (Verheij and Coronel, 1992)
The pummelo thrives in the lowland tropics. For commercial production, elevation not exceeding 400 masl is preferred with optimum temperature of 25-30 C. It can tolerate a wide range of soils from coarse sand to heavy clay. However, it prefers deep, medium-textured, fertile soils free from injurious salts; optimum pH from 5.5 to 6.5; annual rainfall requirement 1500-1800 mm. In the 3 major pummelo provinces of Thailand, the best orchards are situated on the banks of current and former river courses.
Many of the outstanding cultivars from Thailand have been introduced to other countries, commonly with the terms “Siamese” and “Bangkok” attached to their names. Some common cultivars are the ‘Tongdee’ (brilliant gold pomelo), ‘Kao Nam Pueng’ (white honey pomelo) (Tongdee, n.d.), ‘Khao Paen’, ‘Khao Phuang’, ‘Khao Yai’, ‘Khao Taengkwa’, and ‘Tha Khoi’ (Chomchalow, et al., n.d.).
In the Philippines, the common varieties are Amoy Mantan, Magallanes, Panacan, Mintal, Aroman, Sunwui Luk, and Siamese Selections (Loquias, 2006). In China, more than 200 cultivars have been recorded including local and introduced. Of these, about 10 are commercially grown including Shatianyou, Guanximiyou, Wendanyou and Long’anyou (Ganjun, 2009).
Plant Propagation. - Pummelo can be propagated sexually by seed or asexually by air layering (marcotting) , budding, grafting and stem cuttings. In Southeast Asia, the most common propagation method is air layering. However, when there are certified disease-free mother plants, grafting and budding are recommended. In the Philippines, shield budding is the standard budding method using calamandarin rootstocks. Calamandarin is believed to be a hybrid of the calamondin (xCitrofortunella microcarpa) and mandarin (Citrus reticulata).
Land Preparation and Planting. - In sloping lands and in staggered planting, the farm can be prepared by slashing of the vegetation and clearing of the immediate peripheries of the hills. Otherwise, the land should be prepared thoroughly by plowing and harrowing. If the soil is too acidic, lime should be applied. Holes or pits are then dug about 0.5 m deep and wide.
The plant-to-plant spacing is 8-10 m x 6-8 m, depending on the terrain and soil fertility. This is equivalent to a population density ranging from about 125 to 208 plants per hectare. To ensure supply of nutrients, compost is applied at the bottom of the hole or mixed at about 1/3 proportion with the topsoil which will be used to refill the hole after planting. In general, planting is delayed for at least 15 days if raw manure will be used.
Planting is better done during the onset of the rainy season. But it can be done anytime if rainfall is well distributed throughout the year or where there is irrigation. In Thailand, pummelos are grown on raised beds with ditches in between beds.
Watering. - Watering should be done immediately after planting to ensure contact of the soil and roots and to prevent wilting. The regular supply of water is especially important before flowering and until after harvest. To force early flowering, irrigation is delayed during the dry season until the trees show signs of wilting. The wilting trees are then irrigated. To sustain new shoot growth and the development of flowers and fruits, regular supply of water is needed. A mature pummelo tree may need 100-200 li water daily during dry periods.
Intercropping. - Planting of intercrops like banana on the strips between the rows of pummelo has been practiced to maximize utilization of vacant farm spaces, provide shade and protection from wind, and serve as cash crops during the juvenile stage of the main crop. Annual intercrops will also serve as covercrop.
Weeding. -Just like other crops, pummelo needs regular weeding to eliminate competition for soil moisture and nutrients. The uprooted weeds can be piled around the base of the trees to serve as mulch.
Pruning. - At 4-6 months after planting, the trees are pruned to induce branching. This is done by top pruning about 30-40 cm from the ground. 3 branches which are evenly distributed in separate horizontal directions are retained and allowed to develop.
Fertilizing. - Proper fertilization is a standard cultural practice in fruit production, especially in association with floral induction. A practice in Nakhon Prathom, Thailand is to apply 5 kg complete fertilizer per tree per year split into 6 applications or every two months. Foliar fertilizer is also applied every new flushes. In the last application before harvest, NPK combination of 13-13-21 is used to improve fruit taste. In other parts of the country, 2-split applications are recommended, the first before flowering and the second 4-6 months later. (Verheij and Coronel, 1992).
In the Philippines, the recommended rate of fertilizer per year increases from 5-20 kg organic and 4-15 inorganic fertilizer for each bearing tree, depending on age. The fertilizer is applied in holes about 1-2 meters from the trunk. Spraying of foliar fertilizer is likewise recommended every 20-day interval starting at 40 until 140 days after fruit set. (Loquias, 2006)
Pests and Diseases Control. - All pests of citrus also attack the pummelo plant. These include the common leafminers (Phyllocnistis citrella), leaf-eating caterpillars, fruit-boring caterpillar (Citripestis sp.), scales, red mites, fruit flies, nematodes and rats.
The major disease of pummelo is the bacterial canker caused by Xanthomonas citri. Symptoms are characterized by oily spots on the leaves and fruits which later turn brown and corky. Control methods include defoliation and, in severely infected plants, burning to prevent spread.
Other diseases are the root rot, gummosis on the trunk and brown rot of the fruit, all of which are caused by the Phytophthora fungi. Both fruits and leaves are also infected by scab caused by Elsinoe fawcetti. To control fungal diseases, repeated spray of chemical fungicides is recommended. The leaves, fruits and sometimes the branches are likewise prone to sooty mold which is caused by Capnodium citri or Miliola citricola. Sooty mold can be prevented by proper insect pest control.
A recent innovation to prevent serious damage due to insect pests and diseases is the bagging of fruits.
Harvesting. - The pummelos are picked at maturity which occurs about 140-160 days from fruit set. The dull skin of the fruit brightens upon ripening as the oil glands become more prominent and shiny. This change starts near the tip of the fruit and progresses towards the stalk.
Chomchalow, N., Somsri, S. and P.N. Songkhla. n.d. Market trends and export of Thai fruits. Retrieved October 26, 2010 from http://www.itfnet.org/gfruit/Slides/Session%201/Market%20Trends%20and%20Export%20of%20Thai%20Fruits.pdf.
FAOSTAT. 2010. http://faostat.fao.org/site/339/default.aspx, accessed October 25, 2010.
Ganjun, Y. 2009. The Pomelo Industry in China. Retrieved October 26, 2010 from http://www.itfnet.org/source/mainpage/newsAndEvent/contents/PDF_seminar2009/11.pdf.
Loquias, V.L. 2006. Good agricultural practices in pummelo production. Retrieved October 25, 2010 from http://hvcc.da.gov.ph/pdf/pummelo_prodn.pdf.
Verheij, E.W.M. and R.E. Coronel (eds.). 1992. Edible fruits and nuts. Plant Resources of South-East Asia No. 2. Bogor, Indonesia: Prosea Foundation. pp. 128-131.
(Ben G. Bareja 2010)