|General description : The thurian-thet is a small slender evergreen tree of the Annonaceae family.
It can grow up to a height of about 7 m. The tree thrives best in the tropical lowlands on rich deep loam.
Among the cultivated Annona species thurian-thet, having few cultural requirements, is the easiest grow and has prolific fruiting capacities. However, it is the least hardy of the Annona species, requiring a warm and humid tropical climate. It grows at elevations up to 1,000 m and as far as 20°N and 25°S in sheltered sites.
Growth and fruiting are severely set back by cold spells and light frosts kill the tree (Nakasone, 1972). A dry season enhances leaf fall and synchronizes extension growth and flowering to some extent. Yields may be higher under these conditions, provided that high humidity prevails during the period of fruit set.
Where humidity tends to be low, a sheltered site is recommended to reduce transpiration, as the tree is also shallow-rooted.
This is why thurian-thet is commonly found growing in the southern and eastern parts of Thailand where humidity is rather high throughout the year due to frequent rainfall.
Thurian-thet can be grown in most soils with good drainage, as the tree does not tolerate waterlogging.
Vernacular names :Soursop (English); guanábana (Spanish), corossol (French), sirsak, nangka belanda, nangka seberang (Indonesian); durian blanda, durian benggala, durian makkah (Malaysia); saua sap (Papua New Guinea); guayabano (Philippines); tiep banla, tiep barang (Cambodia); khan thalot (Laos); thurian-thet, thurian-khaek (Thailand); mang câù-xiêm (Viet Nam).
Botanical characters : The leaves are oblong-obovate, 8-16 ´ 3-7 cm in size, short acuminate at the apex, with 3-7 mm long petiole. Flowers are regular, greenish-yellow, pedicel up to 2.5 cm long with 3 sepals, 6 petals, and numerous stamens with densely pubescent filaments and numerous ovaries.
The ripe fruit is a pseudocarp, long and heart shaped, grows up to 10-20 ´ 15-35 cm, with dark green skin covered with 6 mm long soft spines.
The thurian-thet fruit is the largest among the Annona species, weighing around 1 kg or more.
The flesh or pulp is white, soft, juicy and fragrant. In-between the pulp, numerous brown to blackish seeds are embedded.
Uses : The fruit of thurian-thet can be consumed fresh as a dessert fruit when fully ripe or mixed with ice cream or milk to make a delicious drink. However, more often the puree is consumed after squeezing the pulp through a sieve.
It can be made into a fruit jelly, juice (with the addition of sugar), nectar or syrup.
It is also used in the preparation of ice cream. In Indonesia a sweet cake (dodol sirsak) is made by boiling thurian-thet pulp in water and adding sugar until the mixture hardens.
In the Philippines young thurian-thet fruits with seeds that are still soft are used as a vegetable. Mature but firm fruit may be made into candies of delicate flavour and aroma.
In Thailand and Malaysia where the trees are cultivated mainly in the home garden the thurian-thet fruits are used as a good flavoured nutritional drink.
The fruit consists of about 67.5 percent edible pulp, 20 percent peel, 8 percent seeds and 4 percent core by weight.
It is a good source of vitamin B (0.07 mg/100 g pulp) and vitamin C (20 mg/100 g pulp) and a poor to fair source of calcium and phosphorous (Koesriharti, 1991).
Prospects : At present, this species is confined to home gardens, and because of erratic yield and short shelf-life, there is little expansion of cultivation.
More research on higher yield through improving pollination is needed before the processing industry requirements can be met.
A breakthrough towards production in orchards can be possible if there is enough demand in the processing industry.
The tree is easily propagated and due to its small tree size, which facilitates orchard management, and the short period from planting until first crop, this can greatly reduce the risk involved in commercial production.