Mangosteen seedlings in perforated polybags (left) and in plastic container (right)
For commercial plantings, seedling trees and grafted trees are used. Mangosteen is usually propagated by seed. Seeds lose viability quickly, and must be planted fresh or stored in moist peat moss, sawdust or paper. Germination occurs at 2-3 weeks, and the seedlings are somewhat slow growers. Seedlings need 50-75% shade for the first 3-4 years, then can be grown in full sun. They are sensitive to high levels of fertilizer, and should be fertilized with a dilute fertilizer solution or an organic fertilizer. Trees can be transplanted to the field after 1-2 years, when they are 30 cm or more in height.
Propagation
Propagation by seeds: On average, the fruit produces 4.8 arils (segments) with about 1 to 2 seeds. Seeds will lose viability in 5 days after removal from the fruit, though they are viable for 3 to 5 weeks in the fruit. Viability is also reduced when air moisture content falls below 20%. Seeds packed in lightly dampened peat moss, sphagnum moss or coconut fiber, in airtight containers remained viable for 3 months. Only 22% germination has been realized in seeds packed in ground charcoal (for 15 days). Soaking in water for 24 hours expedites and enhances the rate of germination. Generally, sprouting occurs in 20 to 22 days and is complete in 43 days.
Seeds germinate well only under high seed moisture content. When sowing is delayed by 5 days, germination is reduced by 75%. If seeds need to be transported to distant places, they should be kept in moist coir dust or clean newspaper to prevent dehydration.
Seed selection: Use only plump, large, and healthy seeds from mature fruits for propagation. Seeds from over-mature and decaying fruits give a low percentage of germination and survival.
Seed treatment and germination: Before sowing, soak seeds in water for 12 hours to facilitate testa removal. Removing the testa helps to increase germination and produce uniform seedlings. Soaking the seeds in water for 24 hours will accelerate the rate of germination to within 10-20 days after sowing. In nurseries, sterilise the seeding medium to kill nematodes and fungi. Prepare a sterilisation box 10 m x 2 m and 0.3 m deep. Fill with seeding medium and cover with a plastic sheet for 3 days in the sunshine.
Sowing: Sow seeds 5-10 cm deep and 2-3 cm apart in the seedbed, or in polythene plastic bags in a nursery. Provide the seedbed with 50-60% shade. The germination medium should consist of a mixture of one part each of fine sand, soil, and humus or decayed organic matter such as chicken dung or cow manure. The medium needs to be moisture retentive but well drained. Seeds can be sown in any position, but are normally laid horizontally. Sprouting usually occurs in 2-3 weeks and is complete in about 6 weeks. Water the seeds regularly and maintain high humidity.
Bagging of seedlings: At two- to three-leaf stage, and when the leaves are mature, transplant the seedlings from the nursery bed to individual polythene bags of 20 x 30 cm. Remove the seedling from the seedbed by holding it at its base with one hand, lifting it slowly while digging with the other hand using a blunt stick or trowel. Mix the medium: equal parts of sterilised fine sand, soil, and humus. Half-fill the plastic bag with the medium, tapping it on the ground once or twice to compact the medium.
Set the seedling on top of the soil at the middle of the bag, and then add more medium up to the brim of the bag.
Care of seedlings: Irrigate seedlings after bagging, making sure that medium is fully saturated. Watering over a long period can cause plant nutrients to be leached from the soil. If leaves show yellowing and to replace leached nutrients, apply nitrogen fertilizer such as ammonium sulphate or urea at the rate of 2-4 g per seedling every month, supplemented by foliar fertilizer application every 7-14 days.
Large planting materials (LPM): This method promotes the rapid growth of seedlings in the nursery to the desired size of 100-170 cm or taller. Transfer seedlings to bigger polythene bags measuring 30 x 40 cm or 40 x 40 cm within a year of transplanting to ensure roots have adequate space to grow. Use fertile medium high in organic matter. Set the plants in the nursery 2 plants/m2 to allow faster growth of the seedlings. Grow the plants in the nursery until 1.5-2.0 m tall before field planting. Before moving plants from the nursery for field planting, gradually remove the shade material to acclimatise the plants to the field environment. This reduces mortality in the field.
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Mangosteen seedlings in perforated polybags (left) and in plastic container (right) |
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Vegetative propagation: Grafting has been shown in other tree species to provide precocity, desirable dwarfness and economy for picking and pruning. Mangosteen is mainly propagated through seeds. The practice of using seeds as planting material results in a long juvenile period for the tree.
Conventional vegetative propagation of the mangosteen is difficult. Asexual methods for production of planting materials, including tissue-derived materials are rarely practiced. Although asexual propagation by grafting has been successfully demonstrated to shorten the juvenile period, the resulting the growth of grafted plants is much slower than normal. Results on the performance of mangosteen derived from planting materials other than from seeds are still inconclusive.
Most Garcinia species however, are not compatible with mangosteens. But, m angosteen can be successfully grafted onto rootstocks of G. xanthochymus , G. venulosa and G. hombroniana . Also, it has been reported that G. mangostana is graft compatible with other Garcinia species such as G. kydia and G. morella, but the growth of grafted materials is extremely slow and the tree appears extremely stunted and suckers develop profusely from just below the graft. The tree needs to be staked upright and cannot support regular crop (Gonzales and Anoos 1951).
In Florida, approach-grafting has succeeded only by planting a seed of G. xanthochymus about 3 cm from the base of a mangosteen seedling in a container and, when the stem of the G. xanthochymus seedling has become 3 mm thick, joining it onto the 5-6 mm thick stem of the mangosteen at a point about 10 cm above the soil. When the graft has healed, the G. xanthochymus seedling is beheaded. The mangosteen made good progress having both root systems to grow on, while the G. xanthochymus rootstock developed very little. However, research should be conducted to accelerate seedling growth, for example by using growth regulators, fertilization and irrigation. No comprehensive study had been done to evaluate the potential of the trees until maturity.
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G. mangostana (with large leaves) grafted to G. xanthochymus seedling (with small leaves) |
Cleft grafting has been found to be highly successful ( SCUC, (2006). Plants for rootstocks should be in a state of active growth. Compatible rootstocks include G. mangostana , G. kydia , G. venulosa , and G. morella .
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Vegetatively propagated mangosteen plant which has been derived from cleft grafting (MARDI) |
Vegetatively propagated mangosteen plant which has been derived from top grafting (MARDI) |
Cuttings and air-layers, with or without growth-promoting chemicals, usually fail to root or result in deformed, short-lived plants. In-arching on different rootstocks appeared promising at first in Philippines, but incompatibility has become evident with all, except G. xanthochymus Hook. f. (G. tinctoria Dunn.) or G. lateriflora Bl. Although there are some reports of increased growth using G.tinctoria and G.xanthochymus as nurse stocks, there is still no information proving that earlier or superior production can be achieved from grafted trees.
Preparation of rootstock: Select rootstocks from plants that have been propagated from seedlings and are highly vigorous, about 1.5-2 years of age, about 30-40 cm in height, and with the same stem diameter as that of the scion (1.6- 2.0 cm). Grafting is more successful by having the same stem size for rootstock and scion, because the cambiums or growing tissue can match closely. Put potted seedlings for rootstocks in a shaded area and precondition them by applying 2-4 g of ammonium sulphate per seedling 15-20 days before grafting.
Preparation of scion: Normally, select scions from a healthy mother tree, choosing healthy terminal shoots with semi-hardwood stems (having two semi-hard leaves). However, if large quantities of scions are required, side shoots can be used. Remove the leaves of selected scions 5 to 7 days before cutting. The stem diameter of the scion should match the stem diameter of the rootstock. The scions must be 6-12 cm long, to include a portion of the mature twig. Use a sharp knife, pruning shears, or tree pruner to cut the scion. Wrap scions immediately in moistened newspaper or fresh banana bracts to prevent drying. If the scion source is far from the nursery, the scions can be stored in a styro-foam box to keep them fresh. For better results, graft scions to the rootstock on the same day they are collected.
Grafting procedure: Cut the selected rootstock just above the axil of the last two lower leaves using a clean, sharp knife. The cut must be at right angles to the stem. Make a vertical slit on the rootstock at the centre of the cut surface to a depth of 2-3 cm enough to accommodate the scion. Slice the basal end of the scion into a gently sloping wedge about 2-3 cm long, by cutting two opposite sides with a swift stroke in one direction downwards. The wedge-shaped scion is inserted into V-shaped opening/slit on the rootstock, making sure that both rootstock and scion are in contact. Wrap the completed graft with Parafilm or polythene plastic strips about 1.5 cm wide and 30-40 cm long. Wrap from the insertion point down until the whole length of the slit is covered. Tie carefully to avoid movement at the point of union and to prevent moisture from entering the graft. Cover the plant with a clear plastic bag and place under shade If a mist chamber is available the plastic bag is not necessary.
Care of newly grafted seedlings in the nursery: The newly grafted plants must be kept under 75% shades. A high relative humidity is essential to promote callus growth at the cut surfaces and to prevent drying of the scion. Water the plants regularly but do not drench the bud. After a new shoot emerges, about one month after grafting, remove the plastic cover. Plastic binding should remain on the grafted plant until union is observed, normally in 30-40 days. Gradually expose the grafted plants to direct sunlight to harden them. The plant is hardened when the youngest leaves are mature or dark green. It is not recommended to transplant grafted seedlings with new flushes of young leaves. At this stage, the plant is vulnerable to stress. Transplant between flushes.