The name rose apple may refer to any of the following fruits in the Syzygium species, such as Syzygium aqueum, S. jambos, S. malaccense, and S. samarangense. Like other fruits named “apple”, the rose apple does not resemble the apple fruit. “Rose apple” might be derived from the fruit’s taste: rose water with a hint of apple.
While rose apple may refer to several species, S. malaccense and S. samarangense remain the popular commercial varieties. Other common names are wax apple, water apple, and malay apple. The fruit is a minor tropical crop in China, Taiwan, Malaysia, Indonesia, Thailand, Melanesia, Polynesia, Micronesia, Latin America, Caribbean, and even sold to niche markets in the USA and Europe.
Rose Apple is flowering tree native to Malaysia, Indonesia, and Vietnam but had been introduced to the rest of the tropics. Because it is valued for large delicious fruits, issues on seasonality and short shelf life has intensified research in postharvest management to make it commercially viable for export.
The tree is strictly tropical, growing in humid climates with an annual rainfall of at least 152cm and is susceptible to damage from freezing temperatures. It grows fast, reaching 12-18m with a trunk up to 4.5m in circumference. It can grow to 12–18m high at an altitude of up to 2,740m above sea level.
It usually flowers at the start of the hot season, bearing fruit up to three months after. The abundant flowers are mildly fragrant, hidden by the foliage until they fall.
The fruits grow prolifically but larger fruits are achieved by thinning the crop and adequate watering. The fruit is commonly oblong bell-shaped and dark red in color, but some varieties have white, green, or pink skins. The flesh is white and surrounds a large seed. Yields have been reported at 21-85kg per tree.
Different rose apple varieties have distinct fruit color. Commercial varieties are red but less common ones can have green, deep purple, white, bluish-black, and white fruits. They have not been given taxonomic rank but have different names in Polynesia and Micronesia.
The major cultivars grown in Taiwan are ‘Pink’ and ‘Big Fruit’, accounting for nearly 80% of production. ‘Thub Thim Chan’ from Thailand, ‘Indonesian Big Fruit’ from Indonesia, ‘Vietnam White’ from Vietnam, and ‘Big Red ‘ from Malaysia are also popular varieties.
Soil and Climate
Rose apple requires well-drained deep loam soil for optimum growth and fruiting. Heavy or light sandy soils should be avoided. Plant growth is also affected in saline soil.
The tree prefers dry weather for flowering and fruiting. Early rains are beneficial to growth, development, and ripening of fruits.
Major propagation is done through cutting, marcotting, air layering, and grafting. Although seeds can be used to cultivate rose apple, high quality of fruits can be maintained through vegetative propagation such as grafting, marcotting, air-layering, and cuttings. For grafting, use 1-2 year old rootstocks from healthy, vigorously growing trees and buds from high-yielding trees.
Indole-3-butyric acid treatments can help rooting in air-layering and cuttings. Air-layering is ideal for young branches (1-2 years old) with a diameter of 1-2 cm and length of 30-45 cm. Meanwhile, rooted cuttings are ready for transplanting after 6 weeks.
It is ideal to perform field planting during the rainy season, to increase the success of establishment. Generally, plants should be transplanted with the soil ball intact, at a distance of 6-9m in planting holes filled with top soil and farmyard manure.
Trees require little to no maintenance other than weed elimination, periodic fertilization, and appropriate irrigation.
First year application of 15:15:15 compound fertilizer and 5kg of organic matter at 1.5 kg/year is recommended. From 2nd year onwards, compound fertilizer of 12:12:7:2 and organic matter are recommended. In Taiwan, trees of over 7 years are applied annually with 1,200-1,600g of N, P2O5 and K2O and 2.6 – 3.4kg of urea per plant including 10-20 tons of organic matter per hectare.
Flowering is induced in Taiwan by flooding, girdling, and root pruning. Black net shading is sometimes used to improve fruit quality.
Pests and Diseases
The tree is fairly tolerant to diseases. Trunks are also vulnerable to termite attacks. Foliage is affected by sap-feeders, defoliators, miners, and borers. Beetles often attack the foliage of young trees. However fruit fly is the major pest of rose apple as they lay eggs on fruits, resulting in larvae boring into the flesh. They can be controlled by bagging the fruits and appropriate field sanitation practices. Infested fruits on the tree and the ground should be removed and the soil under the tree should be dug to remove the pupae.
Harvesting and Postharvest
Because of thin and easily dehydrated fruit skin, fruits have to be graded and packed immediately after harvesting. It is ideal to harvest in the morning, transport in the afternoon, and sell the next morning.
After harvesting, fruits should be kept in plastic crates and stored in a cool place. Graded fruits should be fitted with styrofoam net before transporting to the market. Fruits are packed in traditional 12-15 kg cardboard boxes that are separated into 2 – 3 layers and lined with shredded paper to minimize damage.
The ripe fruit is eaten raw. The crispy fruit has a light sweet taste and can be a refreshing addition to mixed fruit salads. It is not suited for jam and jellies but the half-ripened fruit is pickled or preserved in South East Asia.
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