Pomelo (citrus maxima), "suha" or "lukban" in local dialect is one of the most popular species of the citrus family. It has a long shelf life that it can be transported to distant markets. Pummelo varieties include Siamese Abulug, Amoy Mantan The tree grows from 5-15 meters in height and has low spreading branches with a canopy size ranging from 5-9 meters.
Planting of citrus fruit trees particularly pummelo, calamansi, oranges and mandarin is very suitable to the Cagayan Valley Region's type of land and climate. There are numerous advantages of cultivating citrus. They are rich in vitamin C and calcium, and possesses good eating qualities when consumed either as fresh or processed into juices. Citrus is also used in the preparation of candies and marmalades and as food additives for flavoring, coloring and perfume. Today, more people are engaged in the cultivation of pummelo because of its economic, nutritional, and medicinal benefits.
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Soil and Climatic Adaptation
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.
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.
Methods of Cultivation
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.
Planting of intercrops like banana and areca palm 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.
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.
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.
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 citrior 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.
Potting of Seedlings and Care Management
Seedlings are ready for potting 21-28 days after germination in "7x12"x 0.003 polyethylene plastic bags containing garden soil and place them in the nursery.
- Avoid transplanting seedlings with deformed root system (goose-neck root).
- Water immediately the newly potted plants.
- Eliminate weeding.
Asexual Propagation and Care of Budded Seedlings
- Rootstocks are ready for budding in 6-8 months after potting.
- Apply nitrogenous fertilizer at least five grams per plant monthly.
- Budding should be done at a height of six to eight inches above the ground level.
- Do not fertilize newly budded plants, unless the bud eye have shown signs of growth.
- Remove the wrap of bud, three weeks after budding.
- To hasten growth of bud-eyes, "lopping" or "cripping" the top of the seedlings two to three inches above the bud is recommended.
- When the bud-eyes started to germinate, decapitate the rootstock one to three inches above the bud-eye union to force growth of the bud-eye or scion.
- Weeding should not be done when the scion are succulent and tender.
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.
Source: Crop Agriculture Review, Date accessed 26 March 2014