Durian Botany
The durian is a member of the plant family Malvaceae. The durian is the fruit of several tree species belonging to the genus Durio (some taxonomists place Durio in a distinct family by itself, Durionaceae).
"Bombacaceae were long recognised as a family of flowering plants or Angiospermae. The family name was based on the type genus Bombax. As is true for many botanical names, circumscription and status of the taxon has varied with taxonomic point of view, and currently the preference is to transfer most of the erstwhile family Bombacaceae to the subfamily Bombacoideae within the family Malvaceae in the order Malvales. The rest of the family were transferred to other taxa, notably the new family Durionaceae. Irrespective of current taxonomic status, many of the species originally included in the Bombacaceae are of considerable ecological, historical, horticultural, and economic importance, such as balsa, kapok, baobab and durian." (Excerpt from Wikipedia)
Family: Bombacaceae (or Durionaceae)
Tribe: Durioneae (is characterized by simple entire penninervate
leaves)
Genus: Durio
Species: Durio zibethinus Linnaeus
There are about 30 recognized Durio species and about nine species produced edible fruits of which zibethinus is the most popular and is known as the common durian.
Durio zibethinus L. is the only species of durian commercially cultivated on a large scale and available outside of its native region. Since the common durian is mainly open-pollinated, it shows many differences in fruit colour, odour, and size of aril or flesh; seed; tree characteristics and growth.
It should be noted that Linnaeus is the correct authority for Durio zibethinus and not J.A. Murray.
The Common Durian - Durio zibethinus L.
Tall conical tree frame of the durian
Durian Tree
The durian tree looks regal and majestic befitting its royal title as "King of Fruits".
In its natural environment in a rainforest, the common durian tree has a tall, broadly conical frame tapering to an apex. It is an evergreen tropical tree with a straight trunk and buttressed base. A matured tree trunk can be 50-120 cm in diameter.
A durian tree usually grow to a height of 30-40 m with some exceptional trees reaching a majestic height of 60 m. However, durian trees seldom exceed 12m when grown as grafted clones in durian orchards. It has a very long life of 80-150 years or more.
Oldest durian tree in Thailand that is believed to be about 210 years old.
See video from 13min 46sec....
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| Oldest durian tree in Thailand |
Durian Wood
Durian wood is classified as softwood, coarse, lightweight and is not durable and seldom used for building construction but is used for making light furniture and clogs. The dark brown bark is rough and peels off irregularly.
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| Straight trunk of D24 |
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| Durian is assigned the Roux's model |
Durian seedlings are fast growing and the main stem or trunk produces numerous strong lateral branches in all directions. Young branches are usually covered with coppery or gray scales.
Some lateral branches are also produced which eventually compete with the main trunk. In matured trees, some of the upper branches are almost horizontal.
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| Durian branches grow out laterally in all directions |
Matured durian tree - straight trunk and horizontal upper branches
A majestic durian tree in Thailand........
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| Grafted durian tree D197 - Musang King |
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| Grafted durian tree is shorter and more compact- clone D197 - Musang King |
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| Erect truck and well-spaced branches - maximum fruit production and easy harvesting |
Durian Roots
Durian roots have different formation depending on whether they are grown from seeds or grafted plant materials. A durian tree grown from seed has one tap root going directly down from the trunk. This tap root produces secondary roots follow by tertiary roots. This same anchoring system is also found in seedlings produced by inarching. |
| Exposed root system of a seedling tree |
In a commercial durian orchard where the trees are grown from marcotted plant materials, the durian tree will not have a primary tap root. Instead it has adventitious or secondary roots growing directly from the base of the trunk.
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| Durian roots are shallow-rooted |
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| Young roots just beneath the soil surface |
Durian is unique as it does not have root hairs. Instead, the roots that absorb water and nutrients are called fungus roots which grow out from the secondary or tertiary roots. They are shallow-rooted and grow only within 45 to 50 cm of the soil surface. Also, about 85% of the roots is contained within the canopy radius of the tree. This is very useful in developing ideal fertilizing and irrigation strategies for the durian.
Durian Leaf
Durian leaves are very distinctive
As a dicotyledon plant, durian leaves are simple and alternate, shaped like a lance, 10–20 cm long and 3-7.5 cm wide with a glossy olive or dull green smooth upper surface and velvety, shiny bronze lower surface due to the dense covering of overlapping hairs or scales.
This unique combination of colours is very attractive as the leaves appear to change colour when the wind blows through the tree. Leaf stalks are round, about 2.5 cm long. Leaf apexes are acuminate. When new leaves first appear, they are folded at the mid-rib. As the leaves mature they stretch out.
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| Folded young leaves of the durian |
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| Leaves of different durian cultivars (Photo DOA Malaysia) |
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| Durian leaves - D24 and D197 (Musang King) |
Flushing - new leaves appear 2 - 5 times a year
Dr. Lim reported in Boosting Durian Productivity that
"polygonal graph analysis of leaf characters can be used to differentiate among durian cultivars from various localities, regions and countries instead of using reproductive characters which entails a long waiting period of 10-12years for seedling trees and 6-8 years for grafted trees.
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| A polygraph of D24 |
However, similar polygonal profiles can be done for fruit characteristics or a combination of leaf and fruit characteristics as identification aids that can be conveniently and accurately developed and used by growers without the employment of sophisticated expensive instrumentation. This technique offers a good alternative to differentiate among cultivars in the absence of a determinative DNA finger printing test for durian and other tropical fruits." (page 81)
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| Flower buds and flowers |
Durian flowers are beautiful. Technically, the common durian flowers are ramiflorous, i.e. the flowers are borne along big branches that are capable of bearing the weight of mature fruits.
Durian flower buds appeared in clusters. One cluster, a cymose inflorescence, consisted of mostly 20 to 30 flower buds. Two or three pedicels diverged at the node of the peduncle. Flower clusters appeared on primary and secondary branches often at vestigial positions where a flower cluster had appeared previously. Cluster hung from a branch with their flowers dangling downwards.
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| Clusters of durian flowers - D24 |
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| Anatomy of durian flower |
The development of floral parts within the bud required more than a month.
(Read the full report at this link HERE )
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| Durian flower |
The flower stalks or pedicels, 5–7 cm long, support globose flower buds 2 cm in diameter, opening to reveal 5–6 cm long, greenish-white flowers.
The tubular calyx has three to five triangular teeth surrounding five petals.
Durian has complete or perfect flowers. Stamens are arranged in five bundles around a pubescent style and protruding capitellate stigma.
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| Cross section Durio zibethinus flower |
There are differences in colour and shape of durian stigmas. Some clones (e.g. D8, D24, D104) have 5-lobed stigmas, whereas some have no lobes. Some stigmas are top-shaped (e.g. D2, D88, D96) while others are broad and flat (e.g. D16, D66). Stigma shape is highly consistent within a clone. Clones D8, D66 and D104 have bright orange stigmas while some have yellow stigmas.
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| An unopened bud and several buds about to open. One bud has already shed its petals and stamens. |
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| A durian flower - D197 or Musang King |
Durian pollen is binucleate (having two nuclei) when shed, and remains viable for approximately 48 hours after shedding if kept at room temperature (Soepadmo and Eow 1977). According to Soepadmo and Eow (1977), the pollen of D. zibethinus is shed singly or in clumps. The pollen of several Thai cultivars of D. zibethinus have been reported to be shed in clumps (Salakpetch et al. 1992).
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| Morphological parts of D197 flowers |
Durians typically have two seasons during the year, a major and a minor one. The same trees do not necessarily bear fruits in both seasons.
Durian Flowering
It has been reported that flowering in durian is naturally stimulated by the onset of the dry season.
In peninsular Malaysia, it is generally believed that a dry spell and water stress would stimulate the durian to initiate flowering.
A study conducted in Jerantut, Pahang found that a minimum 18 days of dryness with an average rainfall of not more than 1 mm/day during that period was required to initiate flowering. The flower buds started to emerge 20 days after 8 days of stress and they started to bloom 8 weeks later. The fruit started to fall 90-120 days after blooming depending on the stress intensity and durian clones. The fruit drop season lasted for 30-45 days. Regular rain from one week before fruit-drop and during fruit-drop caused uneven fruit ripening. (Nawi Che Yusoff and Ester Hui TT, Prediction of Durian Season Based on Drought Record, Prosiding Seminar Durian, 2000).
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| Emerging floral buds - variety Musang King D197 |
In Thailand, durian flowering usually occurs after a dry period which should occur continuously for 7-14 days. Low temperatures, about 20-22°C, and relative humidity, 50-60 %, are factors required for flower development. (Surmsuk Salakpetch, Durian (Durio zibethinus L.) Flowering, Fruit Set and Pruning in Proceedings, Fifteenth Annual International Tropical Fruit Conference, October 21-23, 2005, Hawaii).
In Australia, seasonal fluctuations in weather conditions were found to influence the flowering and fruiting phenology and reproductive biology of durian grown around Darwin. Several cool nights below 15°C could cause the appearance of floral protuberances on branches 1-2 weeks after, followed by flowering 4-6 weeks later. Flowering was found to occur in consecutive overlapping cycles in tandem with alternating cycles of cool, dry nights below 25°C and above 15°C. This flowering cycle gave rise to an extended flowering period for 2-3 months and it took 110 to 130 days from anthesis to fruit ripening (Lim TK in Boosting Durian Productivity, RIRDC Project DNT- 13A).
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| (Source: Lim TK) Appearance of pimple protuberances |
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| Floral bud initiation (red arrow) -Durian Musang King D197 |
Flowering can also be induced out-of-season after drying the soil by covering with plastic sheets, or through the use of plant growth regulators.
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| Plastic mulches are used to induce out-of-season flowering in Vietnam |
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The flowering of the durian in the Eastern region of Thailand:
"Durian flowers are borne in clusters on main and lateral branches, but are not found on the trunk. Each inflorescence contains 8 to 20 or more, large pendulous flowers. It takes about 2 months for flowers to progress from emergence to full bloom.
At flower opening, the green epicalyx splits to reveal 5 slightly golden united sepals and 5 yellowish white petals. A large receptive stigma, which is covered with stigmatic fluid, protrudes at about 1 p.m., about 2 hours before opening, and remains in that condition until the following morning, which is approximately 18 to 20 hours after being receptive.
Durian flowers usually open in the late afternoon, but anther dehiscence does not occur until about 6 to 7 p.m. or later depending on the variety. By midnight, all flower parts including stamens, and except for the pistil, fall to ground.
However, all flower parts may remain attached until the following morning if the recommended water management regimes described below are applied during the floral growth and development stage."
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| Durian sepal, petals and stamens (inset: stamens) lying on the ground (cultivar D197) |
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| Fallen petals and stamens littered the ground beneath the durian trees |
The petals of this durian tree is reddish. Mr. Kok from Seremban acquired this durian species from the jungles about 10 years and had bud-grafted about 40 to 50 trees in his farm.
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However, some cultivars or clones such as the Thai Chanee and Kanyao are self-compatible but natural fruit set is very low. It has been reported that in natural and self-pollinated Chanee, the fruit seed is 0 to 6%; and in Kanyao 21%. Research has found that with hand-pollination, carried out over a 2-week period and using pollen from different cultivars, fruit set percentages for Chanee increased to 30-64% and in Kanyao 87-90% .
It is common to find a lone durian tree bearing lots of flowers but no fruits. This tree is usually found in an urban area and completely isolated from other durian trees. The durian's self-incompatibility and the absence of pollen from other durian trees for cross-pollination are the common reasons why there are no fruits.
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Time-lapse video of durian flowers blooming by Pitan Singhasaneh
Pollination
Durian flowers are large and feathery with copious nectar, and give off a heavy, sour and buttery odour. These features are typical of flowers pollinated by certain species of bats that eat nectar and pollen.
An Australian report showed that the
durian flower nectar was found to be very rich in fructose (6.4%), sucrose (5.4%) and lower in glucose (3.4%) in the ratio of 2:2:1.
It also found that bats, the stingless Trigona bees (beeflies), honey bee Apis dorsata, birds and ants are some the major pollinators of durian although the flower possesses characteristics for bat-pollination, i.e. it is chiropterous.
Video of Cave nectar bat pollinating durian flowers by Merlin Tuttle:
Watch this video on pollination of baobab flowers (Adansonia digitata) by straw-colored fruit bats (Eidolon helvum) in Senegal, West Africa.
It also found that bats, the stingless Trigona bees (beeflies), honey bee Apis dorsata, birds and ants are some the major pollinators of durian although the flower possesses characteristics for bat-pollination, i.e. it is chiropterous.
Video of Cave nectar bat pollinating durian flowers by Merlin Tuttle:
Cave nectar bat pollinating durian flower (Source credit: Merlin Tuttle)
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| Honey bee Apis dorsata (Photo credit: Wikipedia) |
Watch this video on pollination of baobab flowers (Adansonia digitata) by straw-colored fruit bats (Eidolon helvum) in Senegal, West Africa.
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| Fruit bat pollinating baobab flower in Senegal (sfrs/CNDP 1984) |
Another research conducted in Malaysia in the 1970s found that durians were pollinated almost exclusively by cave fruit bats, or also known as Pterodids. Cave nectar bat (Eonycteris spelaea), and the long-tongued nectar bat (Macroglossus minimus) are two nectarivorous bats responsible for pollinating durian flowers.
A fruit bat feeding on durian flower nectar during the night
Head of a cave fruit bat - E. spelaea
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| Photo credit: Kelly Tan |
The importance of bats - No Bats, No Durians - Read more HERE
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| Long-tongued nectar bat (Macroglossus minimus) Photo credit: Wikipedia |
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Assisted Hand Pollination of Durian In Thailand
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The following is an abstract of a research article entitled:
The pollination ecology of durian (Durio zibethinus) in southern Thailand
Sara Bumrungsri, Ekapong Sripaoraya,
Thanongsak Chongsiri, Kitichate Sridith
and Paul A. Racey
Abstract:
The floral biology and pollination ecology of durian, Durio zibethinus, were determined in eight
semi-wild trees in mixed-fruit orchards in southern Thailand during April-May 2003 and 2005.
Flowers open fully at 16h00–16h30 and most androecia drop around 01h00. Anthers dehisce
at 19h30–20h00 when the stigmata are already receptive. In a series of pollination experiments,
fruit was set in all treatments within 10 d. The greatest pollination success occurred after
hand-crossed (76.6%), open (54.4%) and emasculation pollination (53.3%). Consistently,
hand-crossed (12.2%), emasculation (8.7%) and open pollination (5.1%) yielded a substantial
fruit set 2 mo after the pollination experiments. Very low pollination success in facilitated
autogamy suggests that most durian trees are highly self incompatible. No mature fruit
was found after insect pollination and automatic autogamy. Fruit bats, especiallyEonycteris spelaea,
are the major pollinators of this durian although the giant honey bee (Apis dorsata) was the
most frequent visitor to the flowers. Bats visited durian flowers at the rate of 26.1 (SD = 20.7)
visits per inflorescence per night. Since this semi-wild durian depends on fruit bats as its pollinator,
protecting fruit bat populations and their roosts is vital for the production of the durian fruit crop.
semi-wild trees in mixed-fruit orchards in southern Thailand during April-May 2003 and 2005.
Flowers open fully at 16h00–16h30 and most androecia drop around 01h00. Anthers dehisce
at 19h30–20h00 when the stigmata are already receptive. In a series of pollination experiments,
fruit was set in all treatments within 10 d. The greatest pollination success occurred after
hand-crossed (76.6%), open (54.4%) and emasculation pollination (53.3%). Consistently,
hand-crossed (12.2%), emasculation (8.7%) and open pollination (5.1%) yielded a substantial
fruit set 2 mo after the pollination experiments. Very low pollination success in facilitated
autogamy suggests that most durian trees are highly self incompatible. No mature fruit
was found after insect pollination and automatic autogamy. Fruit bats, especiallyEonycteris spelaea,
are the major pollinators of this durian although the giant honey bee (Apis dorsata) was the
most frequent visitor to the flowers. Bats visited durian flowers at the rate of 26.1 (SD = 20.7)
visits per inflorescence per night. Since this semi-wild durian depends on fruit bats as its pollinator,
protecting fruit bat populations and their roosts is vital for the production of the durian fruit crop.
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"So what do these bats feed on when the durian is not in bloom?"
If these bats relied only on durian flowers, they would starve to death.
Mangrove trees like the Perepat (Sonneratia) have similar pom-pom-like flowers like the durian. Bats also feed on the nectar and pollen produced by these trees.
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The King's Batty Attendants
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| Mangrove trees like the Perepat (Sonneratia) have similar flowers |
If these bats relied only on durian flowers, they would starve to death.
Mangrove trees like the Perepat (Sonneratia) have similar pom-pom-like flowers like the durian. Bats also feed on the nectar and pollen produced by these trees.
The King's Batty Attendants
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| Blossom bat feeding on durian flower nectar (Credit: Wild Wings and Swampy Things) |
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| Moth feeding on durian flower nectar (Credit: Wild Wings and Swampy Things) |
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Additional Information On Pollination
Watch this video if you are interested to know how new varieties of fruits such as durians are produced. The principles used for apples are the same for durians.
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Durian Fruit Development
Durian fruit development takes about 95–130 days after pollination depending on the varieties or cultivars. Fruit ripening usually heralds the end of the dry season and the on-set of the rainy season.
Watch how the flowers developed and became fruits in the following video:
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| D197 fruit-lets. Remnants of the pistil at the fruit apex as the fruit develops. |
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| Young durian fruitlets of D24. |
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| A bunch of D24 durians |
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| Durian fruits of D197 or Musang King at various stages of ripening on a branch |
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| Durian of different shapes and sizes |
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| Durian with prominent ridges |
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| Round shapes of D24 |
Durian Fruit
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| Peduncle or fruit stalk with the bulging abscission zone |
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| Peduncle or fruit stalk with the bulging abscission zone |
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| A ripe durian prevented from falling to the ground by rafia string |
The durian fruit is famous for its strong odor and unique taste. The fruit is large (between 2 and 5 kg), pendulous, round to oblong in shape, covered with strong sharp spines or thorns. The husk or pericarp is yellow–green to green or brown in color and does not change significantly with ripening.
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| Morphological structure of an opened durian fruit |
The durian fruit is an indehiscent multilocular capsule which is composed of several fused carpels. The durian may have three to seven carpels. However, the common durian fruit usually has five carpels.
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| Cross-section of a 6-7 week durian fruit |
Carpels are the innermost parts of a complete flower and they are united to form the gynaoecium (pistil). The durian capsule is indehiscent i.e. it does not split open spontaneously when ripe to disperse its contents. The fruit drops naturally to the ground when ripe. At this stage, the aril (pulp or flesh) is sweet and soft with a strong aroma.
It has been reported that water loss and ethylene production are the two main factors that cause the ripened durian fruit to dehisce. Water loss causes the husk to shrink and pull the carpels from each other along the suture at the middle of each locule. Ethylene weakens the cells in the dehiscence zone which consists of parenchyma cells without chlorophyll.
In each carpel, the locule or chamber holds one to seven large brown seeds (the ovules) covered in the edible flesh. The edible section is technically called aril or arillus. It is a specialized fleshy outgrowth from the funiculus (or hilum) (attachment point of the seed) that covers or is attached to the seed. It starts to form as a white sheet four weeks after successful flower pollination and fertilization.
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Five locules of an opened durian fruit. Only 3 locules have arils - 2 are empty- XO variety
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The aril varies extensively between cultivars in color, aroma, flavor, texture, thickness, and color. As the fruit matures, the flesh softens and the whitish color changes to cream, yellow or deep orange, and the characteristic smell of the durian becomes more defined.
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| Foreground: unripe arils with whitish tissue on the surface |
Some carpels or locules have incomplete and infertile seeds due to lack of pollination. Some cultivars or clones exhibit this undesirable characteristic more regularly than with others (e.g. cultivar XO above).
The shape of durian fruits is affected by the presence of seeds. Locules containing unfertilized ovules tend not to develop, and thus the fruits become uneven in shape. Fruit shape greatly affects marketability and thus an understanding of pollination and its effect on durian fruit development is
important for the improvement of durian.
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| The ovules in the top locule is not fertilized giving rise to uneven fruit shape |
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| A developed seed and several under-developed seeds |
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| Clone D2 (Dato Nina) exhibiting malformed or shriveled seeds due to absence of cotyledons (right section) |
Strong smell is the durian’s strategy of getting its seeds dispersed.
The characteristic strong odour and flavour is due to the production of volatile compounds. More than 40 volatile flavouring compounds have been identified from durian samples from various cultivars or varieties. Some research indicate that the odour originates from a complex mixture of thiols, esters, thioethers and sulfides. Read how scientists describe the Thai durian smell HERE.
Nutrient Content
The durian arils typically comprise 15–35% of the fruit weight, and are composed of about 2.5% protein, 2.5% fat, 28% carbohydrate and 67% water, with smaller amounts of fiber, minerals and vitamins.
Below are some interesting nutrition facts about the durian provided by the United States Department of Agriculture.
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| Source: The USDA National Nutrient Database for Standard Reference |
Ripe durian arils packaged in foam trays and wrapped with plastic or PVC film are a familiar sight in supermarkets and getting popular with customers.
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| Fresh durian fruits and durian flesh in PVC-wrapped foam tray |
Durian fruit is preserved by freezing, or in the form of a paste or cake that is used to flavour ice-cream, bread or pastries, or the fruit can be fermented, salted or boiled in sugar syrup.
Durian Seeds
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| Durain seeds of 3 popular Malaysian cultivars |
Durian seeds are round or heart-shaped with yellow-brown or red-brown colour depending on the cultivars.
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| Durian seed - bottom shows opened seed with embryo enclosed by the cotyledons |
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| Unfertilized and shriveled durian seeds |
Left: Boiled (darker color) durian seeds. Right: Fresh (lighter color) seeds
Durian seeds are poisonous when eaten raw
but are very palatable when boiled, fried or
roasted and have a texture that is similar
to taro or yam, but stickier.
Durian seeds - various stages of germination (right: about 7 days old)
