|Overview of Rambutan Phenology, Flowering, and Fruit Set in Hawaii
Andrea M. Kawabata
Mike A. Nagao
Darsen F. Aoki
Kendra Y. Hara
Laura K. Pena
University of Hawaii
College of Tropical Agriculture and Human Resources
Beaumont Agricultural Research Center
875 Komohana Street
Hilo, Hawaii 96720-2757
Rambutan (Nephelium lappaceum Lim.) is an evergreen fruit tree that originates from the Malaysian Peninsula. This tree belongs to the Sapindaceae family which also includes lychee (Litchi chinensis Sonn.), longan (Dimocarpus longan Lour.), and pulasan (Nephelium mutabile Blume).
Rambutan is typically grown in regions within 18° of the equator and below elevations of 1,625 feet. This tree requires approximately 80-200 inches of rainfall annually (Tindall, 1994a) and diurnal temperatures that fluctuate between 72°F and 90°F (Lim and Diczbalis, 1998). Rambutan fruit are eaten fresh, canned, prepared in dishes, used as a garnish and made into a drink.
According to the Hawai´i Agricultural Statistics service, in 2003, 39% of the tropical fruit market was comprised of rambutan sales which totaled $834,000. Rambutan is highest grossing exotic tropical fruit crop in Hawaii (HASS, 2004).
There are approximately 30 important cultivars grown in Malaysia (Tindall, 1994b). In Hawaii, only about 10 cultivars have been established. High yield, large fruit size, satisfactory sweetness, appearance, and regular cropping are criteria for selecting a cultivar. Perhaps the most appealing attribute of an excellent cultivar is a tree that produces fruit with aril (flesh) that does not adhere to the testa (seed covering) (Tindall, 1994a). Popular cultivars in Hawaii include ‘Jitlee’, ‘Binjai’, ‘R156 Red’, ‘R167’, ‘R134’, and ‘R9’. The cultivar ‘Silengkeng’ is favored for its large panicles and is a reliable pollinator.
The cultivation of rambutan in Hawaii is different from many south-east Asian countries and Australia. Surrounded by vast ocean, Hawaii’s climate is stable with little variation throughout the year. Steady rainfall and warm temperatures allow Hawaii’s rambutan trees to grow year-round. As a result, terminal maturation is inconsistent within the tree and throughout an orchard. Synchrony of flowering, fruit set, and harvest throughout an orchard becomes extremely difficult to acquire. Monitoring weather data and correlating that to phenological patterns on rambutan trees can help in predicting crop production. This data may be used in future studies to create a crop model for rambutan cultivation.
Hawaii’s climate varies with location and elevation. As such, weather data loggers are used to collect precipitation, temperature, and other climatic information. In Hawaii, rambutan is grown mainly on the east side of the Big Island to remain within its native growing parameters.
Data from weather loggers at the Hilo Airport (38 feet elevation) and Waiakea Experiment Station in Panaewa (574 feet elevation) were been collected for 2002-2004. Data from these loggers suggests that heavier rainfall typically occurs during the winter (November to December) and spring months (March to April) with light showers taking place during the summer (July to August). In Hawaii, the hurricane season runs from June to November which can bring in heavy rains and high winds.
Weather data recorded between 2002 and 2004 at these locations and others suggest that East Hawaii orchards located at elevations less than 845 ft, receive approximately 120 inches of precipitation annually. The average monthly rainfall in Hilo is around 8.4 inches while Panaewa receives nearly 10.5 inches per month.
The weather loggers have shown that monthly rainfall averages can vary greatly from year to year. In January and March 2003, less than 1.5 inches of precipitation was recorded in Hilo for the entire month. Those same months in 2002 and 2004 recorded some of the highest rainfall totals for those years. Although monthly rainfall averages differ between sites, typically, locations at higher elevations receive more rain than near sea level.
Hilo and Panaewa weather data show that minimum and maximum temperatures are stable with minimal variation throughout the year. Monthly maximum temperatures are highest during the months of August and September while monthly minimum temperatures are lowest between December and February. From 2002-2004, minimum and maximum daily temperatures as low as 59°F and as high as 91°F were recorded at the Hilo Airport.
At the Hilo Airport, average monthly temperatures ranged from 62.9-86.3°F. Monthly minimum and maximum temperatures for the Waiakea Experiment Station were lower than those recorded at the Hilo Airport. Waiakea’s average monthly temperatures ranged from 58.7-85.7°F. Hilo’s monthly average minimum and maximum temperatures differed by about 14.7°F. Climate data indicates that sites located below 700 feet, have temperature differences of 2-4°F while differences in temperature between lower and upper elevations up to 2,200 feet, range from 5-11°F. As the location of the planting increases in elevation, there is an increase in temperature difference between daily minimum and maximums.
Chanthaburi, Thailand’s Climate
Chanthaburi lies just north of the Malaysian Peninsula, where rambutan originates. This province of Thailand boasts some of the largest plantations of rambutan and is an important contributor to Thailand’s export market. Thailand is one of the few countries that export rambutan as fresh produce or as a canned product. In most countries, rambutan is sold only in the domestic market.
The weather and climate of Thailand is fairly predictable. Monsoons are common in this area of the world and as a result, wet and dry seasons prevail. According to data collected at Plew Agro-meteorology Station (2005) from 2001-2004, at 78.7 feet elevation, Chanthaburi receives 100-125 inches of rainfall annually.
The monsoon season starts in mid-May and extends through to October. Thailand receives much of its precipitation during these months. In Chanthaburi, it is common to have 20-35 inches of rain during the rainy season, which is typically more rain than Hilo receives in 3 months combined. Rain falls only during a few days out of the month from November to early May, the dry months. In some years, no precipitation is recorded in December and/or January.
From 2001-2004, Chanthaburi’s highest temperature of 93.2°F was recorded during the dry season. The coolest temperature recorded was 59.2°F. The average monthly temperatures ranged from 69.4-92.7°F. Compared to Hawaii, Chanthaburi has an elevated temperature range and receives its minimum temperatures during the hottest times of the year. During the monsoon season, differences between monthly minimum and maximum temperatures are minimal while differences in temperature during the dry season are much greater. The monthly average minimum and maximum temperatures differ by about 14.9°F.
Cairns, Australia’s Climate
Rambutan is also produced in northern Australia where the climate is generally similar to tropical areas. Hawaii and Chanthaburi lie in the northern hemisphere, whereas, Cairns is located in the southern hemisphere or the world. The winter and summer seasons in Cairns are opposite that of Hawaii’s and Chanthaburi’s seasons. Cairns receives cool, dry weather during Hawaii’s summer months and warm, wet weather during Hawaii’s winter months. Weather data collected from Cairns Aero Station (2005) from 1941-2004, shows a pattern similar to that of Chanthaburi. This weather station is located 9.8 ft above sea level.
Cairns’ weather pattern reflects distinct wet and dry seasons. The dry season extends from May to October during which, rainfall is usually less than 3.7 inches each month. The rainy season runs from November to April when up to 17.8 inches of precipitation can fall in a month. Cyclones form during the rainy season and may alter rainfall and temperature data.
Cairns is generally 3°F cooler than Chanthaburi and 2°F warmer than Hilo. However, temperatures recorded during Cairns’ cool season are nearly 2°F below Hilo’s winter temperatures. The highest daily max temperature recorded was 104.9°F while the lowest daily min temperature was 43.2°F. In Cairns, average monthly temperatures range from 62.2°F to 88.5°F. The monthly average minimum and maximum temperatures differ by about 14.8°F.
Rambutan Phenology in Hawaii
Flowering. Rambutan phenology in Hawaii corresponds to Hawaii’s weather patterns. Rambutan flowering is known to be affected by water stress conditions. However, the intensity of flowering, fruit set, and the amount of time to harvest is affected by temperature. Rainfall induces flush formation on the terminals as well as influences fruit size and some physiological problems. Water stress symptoms can be observed as leaf curling. The duration and intensity of water stress, however, still needs to be determined.
Hawaii’s weather is rather stable throughout the year. Instead of having one long dry period during the year like Chanthaburi and Cairns does, Hawaii has two short drier periods during the winter and spring. As a result, two flowering periods are common in Hawaii. Usually one season is more intense than the other, but in some years, the dry spell is not strong enough to elicit sufficient flower development. Three flowering attempts can occur, however, the duration of water stress is usually too brief to induce heavy flowering and poor fruit set and development are often the result.
Flowering occurs 1-2 months after a dry period. The intensity and duration of flower development depends on the intensity of the drought, the maturity of the terminals, and present activity of the plant. Flower development will not occur on terminals that are flushing or immature during the induction period. Off timing and severe pruning can also affect the intensity of flowering. Responsive terminals usually have leaves that are dark green, stems that are dark brown, and exposed to sunlight. Reasons are unknown at this time as to why some mature terminals do not flower after the induction period.
A longer water stress period usually indicates that an extended flowering season will occur. In 2003, there was a month-long drought in January and March along with low rainfall in February. About 3 months later in April, Binjai trees in Onomea began blooming, which continued through August. However, this prediction of heavy flowering with long drought periods is not always accurate. As mentioned earlier, flowering is also dependent on the present status of the tree which includes, tree health and vigor, maturity of the terminals, and present flush or fruit load. Furthermore, soil type influences water retention. Water stress is more evident in rocky, volcanic soil. Whereas, increasing soil organic matter content increases water retention and requires greater drought to induce flowering of rambutan.
Flower initiation may be hindered by heavy fruit set even in the presence of dry weather. In January 2005, dry weather could have initiated flowering on Binjai trees in Onomea; however, nearly 50% of the trees’ canopies had fruit. As a result, flower development was severely suppressed.
In an orchard, flower anthesis usually lasts 2-3 months. However, during extended dry periods, flowering can last up to 5 months on most cultivars. Silengkeng is an unusual cultivar in that flowering can take place for a majority of the year. This cultivar produces large panicles and can take up to 9 months to complete its flowering cycle. On a single panicle, anthesis usually takes 3-7 weeks for cultivars such as R134 and R156 Yellow. Silengkeng panicles can take up to 23 weeks to complete anthesis.
According to Tindall (1994a), three types of rambutan trees based on the types of flowers that are produced on the tree. They are:
Male tree which produces staminate male flowers
Trees that produce only hermaphroditic functionally female flowers
Trees that produce both hermaphroditic functionally male and female flowers
Staminate male flowers are produced only on male trees. Male tree panicles take approximately 24-46 days to complete anthesis. These trees act only as pollinators and do not produce fruit.
Some rambutan trees only produce hermaphroditic functionally female flowers. Male trees must be present to pollinate flowers on these trees. Most cultivars grown are selected for their high percentage of hermaphroditic functionally female flowers and low percentage of hermaphroditic functionally male flowers. Functionally female flowers produce pollen cells; however, the anthers on these flowers are indehiscent. Pollen is not distributed from these flowers.
Functionally male flowers are usually produced in the range of 0.05%-0.9% of the total number of flowers (Nakasone and Paull, 1998). Panicles with this combination of male and female flowers tend to produce the male flowers first. Male flower production is greatest in the first 3 weeks and then tapers off. Towards the end of anthesis, nearly all flowers on the panicles are female.
A plant growth hormone called naphthalene acetic acid (NAA) has been shown to convert young functionally female flower buds to functionally male flowers. A treatment of 90 ppm NAA can induce this conversion 6-7 days after the panicles are sprayed with the solution. These functionally male flowers provide pollen for the fertilization of receptive female flowers. A single treatment of NAA induces functional male flower production for 12-15 days. Thereafter, additional panicles must be treated for continual production of dehiscent (pollinator) flowers (Kawabata et.al., 2004).
Flushing. Vegetative flushing on rambutan trees is promoted by rainfall, heavy irrigation, pruning, and harvest. Even in the presence of heavy rainfall, flushing can be reduced by cool weather and heavy fruit set and flowering. Although precipitation is generally high during the winter months, vegetative growth is held to a minimum due to cooler temperatures.
In Hawaii, flushing is highly non-synchronous. Since the weather in Hawaii is fairly stable, precipitation can cause vegetative growth to occur at any time of the year. Unlike Chanthaburi and Cairns, Hawaii does not have a long dry period where the terminals are allowed sufficient time to mature and be at a state of rest during the flower induction period. Pruning may synchronize flushes for a certain length of time; however, some branches mature faster than others and some branches respond to rainfall sooner than others. Continuous moisture in the soil increases the potential that flushing will occur during the flower induction period when the terminals are supposed to be at rest.
In order for flowering to occur, rambutan terminals must be mature and at rest meaning that vegetative growth cannot be taking place. In Hawaii, new flushes take 3-4 months to mature. There are 2 growth seasons that occur from May to June and August to September. This period of growth generally takes place after fruit harvest when the branches are also pruned. An extended flowering season additionally causes the synchrony of terminal maturity to be altered. If the flowering season is extended, fruit development will in turn be prolonged, and harvesting will be lengthened by several months. This means that branches that flowered early in the season will be harvested first, allowing those to flush while fruit still remain to be harvested on branches that flowered later in the season.
Fruiting. Fruit development begins shortly after anthesis. Although there are two ovaries present on a female flower, one ovary is aborted leaving the other to develop into a normal fruit. Occasionally, both ovaries will develop and two fruits will mature on the same peduncle. Rambutan fruit are green when immature and eventually turn red or yellow which is cultivar dependent.
The rambutan fruit growth curve is sigmoidal. Early in fruit development, rambutan fruit increase slowly in size and weight. The growth curve begins increasing exponentially when seed filling and aril development take place. Seed filling occurs 8-10 weeks after anthesis. Aril development begins from the tenth to twelfth week after anthesis. Four to six weeks later, fruit growth tapers off. During these last few weeks before harvest, fruit color intensifies and total dissolved solid (BRIX) concentrations increase. Refractometers are used to calculate BRIX readings which provide approximate levels of sugar content in the aril of the fruit.
In Hawaii, fruit harvesting begins around the sixteenth week after anthesis. Harvested fruit should provide BRIX readings of 18% or greater. Rambutan are non-climacteric fruit and as such, do not ripen after harvest. Harvesting must be done at the peak of ripeness for overall color, texture, and flavor appeal.
The main season crop ripens in December and January while the minor season crop matures in August and September. Longer days provide more sunlight and warmer temperatures for fruit growing during the main season. These fruit mature faster than the minor season fruit and are harvested 2-4 weeks sooner. At higher elevations, temperatures are cooler. The time to fruit maturation is also lengthened with increasing elevation. On average, harvests take place over a 2-3 month period. Following an extended dry season, fruit harvest may take 3-6 months longer.
Hawaii’s minimum and maximum temperatures are similar to that of Chanthaburi, Thailand and Cairns, Australia. Monthly and daily fluctuations typically do not vary greatly. However, Hawaii’s rainfall patterns are strikingly different from rainfall received in Chanthaburi and Cairns. These locations have distinct wet and dry seasons whereas Hawaii receives consistent moisture for a majority of the year.
As a result of these distinct wet and dry seasons, Chanthburi and Cairns has only one flowering and fruiting season. Hawaii’s flowering and fruiting seasons are split between two seasons. The main flowering taking place in July and August and the main harvest taking place in December and January. A minor season occurs 3-4 months earlier. Table 1 provides a brief overview of flowering, flushing, and fruiting patterns at the three locations.
Stable weather patterns allow rambutan terminals to flush during almost anytime of the year. Obtaining synchronous maturation of the terminals is nearly impossible in Hawaii as a result of the consistent rainfall and temperatures. Flower panicle development requires that the terminals be mature at the time of flower induction. Flower induction takes place following a period of water stress. Each season, a percentage of the terminals are immature during the floral induction period so it is rare to have 100% flowering on a rambutan tree grown in Hawaii.
Although flowering, flushing, and fruit harvesting is somewhat inconsistent, rambutan still remains a viable crop in Hawaii. Growers are optimizing fruit set by incorporating male trees and treating panicles with the plant growth regulator, Naphthalene Acetic Acid (NAA), to improve pollination.
Cairns Aero Weather Station. 2005. Climate averages for Cairns Aero weather station. Australian Government Bureau of Meteorology. Last accessed the World Wide Web on Sept. 18, 2005. http://www.bom.gov.au/climate/averages/tables/cw_031011.shtml.
HASS. 2004. Hawai´i Agricultural Statistics Service. Hawai´i Department of Agriculture. http://www.nass.usda.gov/hi/fruit/tropfrt.htm.
Kawabata, A.M., M.A. Nagao, D.F. Aoki, and K.Y. Hara. 2004. Flowering and fruiting of Sapindaceous crops in Hawaii. In: Proceedings of the 14th Annual International Tropical Fruit Conference.
Lim, T.K. and Y. Diczbalis. 1998. Rambutan: characteristics and cultivars. In: Northern Territory of Australia, Department of Primary Industry and Fisheries Agnote, No. 628(D28):1-3.
Nakasone, H.Y. and R.E. Paull. 1998. Tropical Fruits. CABI Publishing. New York. p. 184.
Plew Agro-meteorology Station. 2005. Temperature and rainfall data from Chanthaburi Horticulture Research Center, Chanthaburi, Thailand. Department of Meteorology.
Tindall, H.D. 1994a. Rambutan cultivation. Food and Agriculture Organization of the United Nations. Rome, Italy. p. 163.
Tindall, H.D. 1994b. Sapindaceous fruits: botany and horticulture. Horticultural Review. 16:143-196.
An Overview of Rambutan Phenology, Flowering, and Fruit Set in Hawai'i
A.M. Kawabata, M.A. Nagao, D.F. Aoki, K.Y. Hara, L.K. Pena
Rambutan is grown in the tropical regions of the world. Chanthaburi, Thailand lies just north of the Malayan Peninsula, where rambutan originated. Monsoons are common in this area. Resulting is a distinct wet (May to Oct.) and dry (Nov. to Apr.) season. Rambutan is also grown in northern Australia. Cairns, Australia has similar climate conditions to Chanthaburi, except that their cool, dry weather occurs during the summer months and the warm, wet weather occurs during the winter months. The weather in Cairns is influenced by cyclones that form during the rainy season. Hawai'i has slightly different climatic conditions than Chanthaburi and Cairns. Although Hawai'i has a hurricane season that runs from June to November, the wet and dry seasons are not as distinct. Hawai'i experiences multiple periods of drier weather over the course of a year. Typically, higher rainfall can be expected during the winter (Nov. to Dec.) and spring (Mar. to Apr.) months with light showers forming during the summer (Jul. to Aug.).
Flower development takes place approximately 1-2 months after a period of water stress. In an orchard, anthesis lasts 2-3 months, but may extend to 5 months during lengthy, dry periods. Cultivars like ‘Silengkeng’, which have large panicles, may continue to flower up to 9 months. In Hawai'i, flower production takes place during the spring (Apr. to May) and summer (Jul. to Aug.). Rambutan in Chanthaburi and Cairns flower once a year following the dry period. Flower production in these areas is usually very intense. In contrast, yearly flowering in Hawai'i is split between the two induction periods. Monoecious cultivars such as ‘Silengkeng’, ‘R156 Yellow’, and ‘R134’ exhibit male flower production that is prolific in the first 2-6 weeks. Anthesis of female flowers coincides with that of male flowers. Female flowers are produced throughout the flowering season. Time of anthesis on a single panicle can range from 3 to 23 weeks.
Maturation of rambutan terminals is non-synchronous in Hawai'i. As a result, flushing can occur at any time in response to a significant amount of rainfall, harvest, or pruning. However, flushing typically occurs 3-4 times over the course of a year. The most pronounced flushing occurs in May. August and November produces smaller flushes. Heavy fruit set may negate the effect of heavy rainfall. Very little flushing takes place during the winter months even in the presence of high precipitation.
Fruit set on a single panicle takes place a few weeks to 2 months after anthesis has commenced. Seed filling begins 8-10 weeks after anthesis. Aril development occurs 10-12 weeks after anthesis. Rambutan fruit are comprised of 75-80% water. Therefore, irrigation is important during fruit development. Irrigated trees may produce fruit that are 10-15% larger. Harvesting takes place 18-20 weeks after anthesis when BRIX readings are 18% or greater. Late-summer and winter harvests are typical. An extended flowering season also prolongs the fruit harvest period.