5. RESULTADOS
5.2. ANÁLISIS DE LOS DATOS
5.2.3. Factores asociados al estado refractivo: Edad
Flowering can be induced by a continuous dry period of 15–30 days, which limits apical bud growth. Three factors play a role in fl ower induction: the threshold leaf water stress, the age of apical buds (at least 10 weeks) and vigorous vegetative growth. The threshold leaf water stress is about –1.0 MPa (Fig. 6.3). This water stress or dry period is followed by two heavy waterings spaced 7 days apart. This irrigation regime can lead 30–35% of the apical buds to produce fl owers. Delaying the irrigation regime can lead to fruit shedding of the early fl owers, while too early induction of irrigation can lead to the remaining buds being vegetative. Fruit set is not a problem, although set of 10–15% of the fl owers can inhibit the remaining buds, leading those buds to vegetative development.
Paclobutrazol (a gibberellin biosynthesis inhibitor) applied as a soil drench or a spray to the leaves and buds also alters the fl owering cycle of mangosteen.
Treated trees fl ower about 40 days sooner. Application as a soil drench has a residual eff ect of 2 years or longer. Coiling a wide band (3 cm) of wire tightly around the trunk, 30–40 cm above the soil, is also reported to induce earlier fl owering.
Table 6.1. The shoot/root ratio of mangosteen seedlings.
Seedling age (months) Shoot-to-root ratio
6 6.24
12 5.75
18 5.5
24 4.94
Fruit
The globose and smooth berry develops parthenocarpically. The fruit is 4–8 cm in diameter and weighs about 80–150 g, with a persistent calyx at the stem end (Fig. 6.1). The pericarp is 5–10 mm thick and turns purple when ripe. The skin contains a bitter yellowish latex and purple-staining juice. The edible white aril (approximately 30% of total fruit weight) occurs in four to
Apical Buds
>8 Weeks Old
Days Heavy Irrigation + Second Irrigation 7 Days Later
Within 2 Weeks
Fig. 6.2. Phenology of steps required to induce fl owering in mangosteen. The tree must be vigorous with bright green leaves and wide and thick leaf blades at fl owering. Flowering intensity depends on plant vigor, apical bud, age and length of the drought period. (After Salakpetch, 1996.)
Time to First Flowers (Days)
–0.50 –0.70 –0.90 –1.10 –1.30
Fig. 6.3. The infl uence of leaf water stress level induced by withholding irrigation on days from onset of irrigation to appearance of fl owers and number of fruit per tree. At a leaf water potential of –0.86 MPa, the leaves show slight wilting while at –0.08 MPa the leaves are noticeably wilted and at –1.12 MPa show severe wilting.
(After Salakpetch et al., 2006.)
eight segments. The one or two segments containing brown, almond-shaped apomictic seeds are larger.
There is no true seed, as the seed develops from the inner carpel wall, is sometimes polyembryonic and has an underdeveloped embryo. At anthesis, it is obvious which fruit segment will be seeded. Fruit development takes 100–120 days from anthesis and up to 180 days in cooler areas or at higher elevations (Fig. 6.4). Growth is initially dominated by the pericarp with aril dry matter, not increasing until 20 days from anthesis and continuing throughout fruit growth.
CULTIVAR DEVELOPMENT
The 2n number has been variously reported as 56–76, 88–90, 96 and 120–
130; the most commonly accepted number is 88–90. The diffi culty is in counting the numerous small chromosomes in shoot tips. Mangosteen is only known as a cultivated plant. Based on morphological characteristics it may be an allopolyploid hybrid, as a female between G. hombroniana Pierre (2n = 48) and G. malaccensis (2n = 42).
Apomictic seed and an absence of male trees or fl owers suggest all trees belong to a single clone. However, some diff erences in tree and fruit shape, rind thickness, leaf shape and area, and petal color do occur. This variation has been confi rmed by molecular DNA markers and may be a result of the accumulation of natural mutations. Another hypothesis is that mangosteen arose from more than one hybridization. The nucellar nature of the seeds,
Time from Anthesis (Days)
Fig. 6.4. Mangosteen fruit growth as dry mass, showing total mass and separate components of the rind, fl esh and seed. (After Poonnachit et al., 1992.)
absence of diversity and long juvenile period (6–15 years) limit selection work.
Collections are maintained in South-east Asia, principally in Thailand and Malaysia. No described cultivars have been reported. The exposure of seed callus and cell cultures to irradiation has produced seedlings with increased genetic variability.
CULTURAL PRACTICES
Propagation and nursery management
The apomictic ‘seeds’ are viable for a short period (3 days, if dried) and are best kept in moist peat moss or left in the fruit. Heavier seeds (>1.3 g) give the best seedling survival, as initial growth is slow. Seeds should be planted in freely draining growing medium under high humidity and shade. On germination (2–3 weeks), a radicle and plumule emerge from opposite ends;
as soon as an adventitious root develops at the base of the young shoot, the radicle dies. Very slow seedling growth is a major problem and is attributed to poor seedling root development, having no root hairs and few laterals. A porous medium is best for seedling growth, with peat moss, bark and coarse sand being ideal. Growth increases signifi cantly when side shoots emerge. The shoots generally emerge from every node.
Grafting onto mangosteen seedlings is not diffi cult, although such plants are slower-growing and small-fruited with a shorter juvenile phase. Other rootstock have been tested with variable results. Positive results have been obtained with top-wedge grafting. Rooting of cuttings and air layers from mature trees have failed, although cuttings from seedling can be rooted under mist.
Field preparation
No specifi c information is available regarding land preparation, although high rates of organic matter are recommended. Practices normally follow recommendations for other tree crops in the area. Deep-ripping is recommended for compacted soils.
Transplanting and spacing
The long, delicate taproot and poor lateral root development mean that transplanting should be performed with care. Planting holes are prepared (1.2 u 1.3 m) in advance and organic matter added a month before transplant.
Plants should have reached 60 cm before transplanting and a deep ball of earth set out, then watered heavily.
Because of the need for shade and humidity, trees are often planted in mixed stands with durian, rambutan and coconut used as the dominant trees. An area of 40–80 m2 is allowed per mangosteen tree and trees 0.6 m high are planted at 8–10 m (110–140 trees/ha) or 11–12 m if a mechanical harvesting aid is to be used. Shade is maintained for 2–4 years, then gradually reduced to full sunlight.
Irrigation practices
Mangosteen trees can withstand some water-logging but not drought, so a constant supply of water is required. A continuous dry period of 15–30 days should be imposed to limit apical bud growth (Fig. 6.2) and encourage fl owering. The recommended crop coeffi cient at this stage is 0.00 (Table 6.2). This dry period is followed by two heavy waterings, spaced about 7 days apart. The trees should then be regularly watered during fruit growth and development at 80–85% of evapotranspiration (Table 6.2). Trickle irrigation or microsprinklers may be ideal for this crop.
Pruning
The regular pyramidal crown and slow overall growth limits pruning.
However, the tall nature of the tree (25 m) and fruit being borne singly make harvesting diffi cult; dwarf rootstocks and pruning may therefore be useful.
Inside shoots and dead branches are removed along with suckers at the base of the main trunk. Water sprouts should also be removed. Severe pruning is never desirable. The limited pruning is carried out when there are no fl owers, fruit or leaf fl ushes.
Table 6.2. The crop coeffi cient (Kc) for mangosteen to estimate the daily water requirement (WR) for different stages of development, based on evapotranspiration (ET). WR = Kcu ET (Hiranpradit et al., 1998).
Stage of development Kc
Vegetative growth 0.60
Floral initiation 0.00
Floral development 0.75
Fruit setting 0.75
Early fruit growth 0.80
Late fruit growth 0.85
Fruit maturity 0.85
Fertilization
Manure is recommended for young trees, along with mulching around the tree base. Non-bearing trees require a low, steady supply of nutrients, applied every 3 or 4 months. One recommendation is for 70 g nitrogen, 6 g phosphorus and 50 g potassium per tree per year until maturity. About 2–7 kg of complete fertilizer (10:10:19) per year is required for mature bearing trees.
Half is applied when vegetative growth is being stimulated after fruit harvest (Fig. 6.2) and the remainder 2–5 weeks after anthesis. Dolomite can be applied at 0.2 kg per tree per year of age to 15 years, with a constant application rate for older trees. Manure is also used.
Pest management
On the Malay Peninsula, Cankers on stems and young and older branches are caused by Zignoella garcineae P. Henn. The foliage on infested branches withers and eventually the whole tree dies. Trees should be cut and destroyed to arrest the spread. Thread blight, caused by Pellicularia koleroga Cooke, has been reported in Puerto Rico under conditions of excess shade and humidity.
The smaller stems are fi rst attacked, with the blight becoming severe when it attacks the leaves forming a whitish fi lm over the blade. The leaves turn a clear brown, then darken before abscising. Removal of some shade and application of a Bordeaux mixture or other copper fungicides give control. Postharvest decay can be caused by Botryodiplodia theobromae.
Only a few insect pests have been reported, possibly due to the bitter sap.
Ants nesting in the tree can damage the growing tips. Mites can attack the fruit surface and make it unattractive for market. Caterpillar larvae and grass hoppers can cause some leaf damage. Fully ripe fruit are attacked by monkeys, rats and bats.
Weed management
The slow growth of young trees means they can be quickly overtaken by weeds. Organic mulch is often used to assist with weed control and reduces evaporation from the soil around the trees. Mulch should not be placed against the tree trunk. Plastic mulch can also be used.
Orchard protection
Shade is essential during the fi rst 2–4 years. Shading (30–50%) can be achieved with mixed stands or crops such as pigeon peas, bananas, plantains,
rambutan, durian and coconut, placed at least 1.5 m from the mangosteen tree. Cloth is also widely used to provide shade. Excessive shade (>50%) produces tall and skinny trees. Cover crops (e.g. Crotalaria, cowpeas, tropical kudzu) also help and have been recommended as long as the area around the tree is clear. Mangosteen trees must be protected from strong winds and salt spray.
HARVESTING AND POSTHARVEST HANDLING Harvesting
The fruit are picked when soft and dark purple with the peduncle attached.
Harvesting is by hand or with a pole and basket every 2–3 days. Mangosteen harvest indices have been based on the extent and intensity of purple pericarp development (Table 6.3). The stage at harvest depends on whether the fruit is intended for the local market or export; export fruit are picked at an earlier
Table 6.3. Mangosteen harvest index stages. Fruit are normally harvested between stages 1–4 and eaten from stages 4–7. The fi nal total soluble solids fi gure was obtained after the fruit was allowed to ripen to stage 5 at 24°C (Tongdee, 1985) and fruit attachment force from the tree (Tongdee and Suwanagul, 1989).
Stage Pericarp color
0 Yellowish-white 2.2 Severe Not
separable
1.19 Moderate Diffi cult Minimum stage
5 Reddish-purple 1.32 None Easy Eating
stage
stage. Fruit should not be harvested before the pericarp is a light greenish-yellow with distinct irregular pink red spots over the entire fruit (stage 1).
Fruit with less color development have excessive latex exudation at the peduncle and an inferior fl avor when they do darken to the full purple stage in about 5 days. Care is essential to avoid mechanical injury, as a 20 cm fall causes signifi cant damage to the aril. Fruit ripening on a tree takes place over 6–12 weeks. The amount of latex declines with maturity, while total soluble solids increase and acidity remains relatively constant after stage 1 (Fig. 6.5).
Burst latex vessels on the fruit skin leave dried yellow latex (gamboge) that may be scraped off .
Postharvest handling
Fruit are graded to remove damaged fruit and for size and color. There are no US or international standards. Fruit are usually sold in single-layer fi berboard cartons of 2.25 kg with padding, sometimes in trays and individually wrapped to prevent injury (20–24 fruit/carton). In South-east Asia, the fruit are sold either in baskets or strung in long bundles of 10–25 fruit. The thick fruit wall hardens as the fruit ripens and during storage at low temperatures (<10°C).
Current practice is to store at 12–14°C for a storage life of about 20 days without chilling injury. Precooling and tray packs are useful. The application of
Maturity Stage
Acidity (% Citric)
Total Soluble Solids (%)
Fig. 6.5. Mangosteen aril acidity and total soluble solids at different maturity stages, as described in Table 6.3. (After Tongdee, 1985.)
surface coating and storage in polyethylene bags reduces fruit weight loss and prevents calyx wilting during storage. It is unclear if the eff ects are due to the prevention of water loss or to the modifi ed atmospheres.
Marketing
The fruit is regarded as a fruit-fl y host, which limits its movement in international trade. Shipments are made by air to Europe, which has no fruit-fl y disinfestation requirements. Harvested fruit can be carefully cut open and the aril inspected before the fruit is frozen whole and shipped to Japan.
Although it has been shown that mangosteen fruit is not a host for oriental fruit fl y (Bactrocera dorsalis [Hendel]), vapor heat treatment is needed before fresh fruit can be exported to Japan.
Fruit damage during harvesting and marketing aff ects 20% or more fruit.
The cause of ‘gamboge’ disorder, where latex seeps into the fl esh giving a bitter taste, is unknown. The disorder makes separation of the aril and surrounding tissue diffi cult even in ripe fruit and leads to pericarp hardening. This should not be confused with impact injury. Pericarp hardening at the point of impact and aril collapse, dehydration and pinking or browning are common signs of injury.
A drop of just 10 cm can cause slight pericarp damage, indicated by hardening at the point of impact. Higher drops cause signifi cantly greater damage, leading to downgrading of the fruit.