Progress 10/01/02 to 09/30/06
Outputs
Rambutan flowering in Hawaii occurs on mature terminals approximately 1-2 months after a period of water stress. Yearly flowering in Hawaii is split between the two induction periods. Flowering can occur during the spring (Apr to May) and summer (Jul to Aug), thus trees encounter flower induction conditions during January to February and during June and July. Anthesis on a single panicle can range from 3 to 7 weeks. Anthesis in an orchard occurs over 2 to 3 months. Seed filling begins 8 to 10 weeks after anthesis and aril (flesh) development occurs 10-12 weeks after anthesis. Harvesting occurs 16-20 weeks after anthesis when BRIX readings are 18% or greater. Late-summer and winter harvests are typical. An extended flowering season will prolong the harvesting season. Maturation of terminal shoots is non-synchronous in Hawai'i. Vegetative flushing can occur in response to a significant amount of rainfall, harvest, or pruning. Flushing typically occurs 3-4 times yearly
with pronounced flushing in May and smaller flushes in August and November. Panicles on grafted rambutan cultivars possess hermaphroditic functionally female flowers (HF) intermingled with a very small percentage (<1.0%) of hermaphroditic functionally male flowers (HM). If seeds are planted, some develop into male trees that never fruit and possess only true male flowers (TM). Anthers on TM release pollen, which are dispersed by wind and insects and pollinate trees bearing HF. The HF, which develop into fruits and number between 200 and 800 on each panicle, do not shed pollen, and cannot pollinate flowers. HF have an ovary and stigma, but their anthers do not dehisce during anthesis. HM are less common during cooler months and resemble HF, but HM anthers shed pollen at anthesis. The TM and HM are the pollen sources during pollination and for fruit set. Deformed, undersized fruits that lack a fleshy aril will be a common occurrence without pollination. Without male trees, pollination
is dependent upon pollen from the low number of HM. The Silengkeng variety naturally produces more HM than other cultivars which makes it a good pollinator tree. Grafted or air layered male trees planted within or around the perimeter of an orchard will also increase availability of pollen during flowering. The plant growth regulator, naphthalene acetic acid (NAA), applied to the hermaphroditic female panicles during early stages of flower opening can induce the development of HM with viable pollen. Aqueous sprays of the K salt of NAA stimulate HM development within 7 to 12 days after treatment. Re-treatment of additional panicles will continue production of HM over the entire flowering season. Collection of data for registration of NAA through the IR4 program is underway.
Impacts
Rambutan flowering in Hawaii can occur during spring and summer, thus growers in Hawaii can produce 2 crops over a 12 month period. Late-summer and winter harvests are typical. Anthesis in an orchard occurs over 2 to 3 months, and harvesting occurs 16 to 20 weeks after anthesis when BRIX readings are 18% or greater. Vegetative flushing typically occurs 3-4 times yearly with pronounced flushing in May and smaller flushes in August and November. Because panicles on grafted rambutan cultivars possess functionally female flowers intermingled with a small percentage (<1.0%) of functionally male flowers, development of deformed fruits lacking a fleshy aril is a common problem in Hawaii due to poor pollination. If seeds are planted, some seedlings develop into male trees that possess only true male flowers. True male and the functionally male flowers are the pollen sources during pollination and for good fruit set. The Silengkeng variety naturally produces a higher proportion
of functionally male flowers and can be planted in the orchard as a pollinator tree. Planting grafted or air layered male trees within or around the perimeter of an orchard also increases the availability of pollen. The plant growth regulator, naphthalene acetic acid (NAA), applied to the female panicles during the early stages of flower opening can induce the development of functionally male flowers with viable pollen. Re-treatment of additional panicles with NAA can continue production of functionally male flowers over the entire flowering season. IR4 registration for NAA use on rambutan is being pursued.
Publications
- Kawabata, A.M., Nagao, M.A., Aoki, D.F., Hara, K.Y.and L.K. Pena. 2005. Overview of rambutan phenology, flowering, and fruit set in Hawaii. Proc. 15th Annual International Tropical Fruit Conference. Hilo, Hawaii. p 6-10.
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Progress 10/01/04 to 09/30/05
Outputs
A multi-year phenology study on rambutan (Nephelium lappaceum) trees in Hawaii is nearing completion and has shown that flowering occurs on mature terminals approximately 1-2 months after a period of water stress. Cupping of the terminal leaves is evident when trees are exposed to sufficient water stress for flower induction. Yearly flowering in Hawaii is split between the two induction periods. Flowering can occur during the spring (April to May) or in summer (July to August) which is the principal flowering period. Thus trees encounter flower induction conditions during January to February and during June and July. Anthesis on a single panicle can occur over a 3 to 7 week period, while anthesis in an orchard can occur over 2 to 3 months. Fruits exhibit a simple sigmoid growth curve with the rapid growth period occurring between 10 and 16 weeks after anthesis. During fruit development seed filling begins 8-10 weeks after anthesis and aril (flesh) development occurs
10-12 weeks after anthesis. Harvesting occurs at 16 weeks after anthesis for fruits developing during warmer periods and 20 weeks for fruits developing during cooler months. At harvest BRIX readings for the aril are 18% or greater. The main harvest season is in winter between December and January with a second and more minor harvest season in late-summer (August to September). An extended flowering season will prolong the harvesting season. During flowering, panicles on the bud grafted rambutan cultivars possess mostly hermaphroditic functionally female flowers intermingled with a very small percentage (<1.0%) of hermaphroditic functionally male flowers. Hermaphroditic functionally female flowers, which develop into fruits and number between 200 and 800 on each panicle, do not shed pollen since the anthers do not dehisce. Anthers on hermaphroditic functionally male flowers dehisce and shed pollen, but the absence of sufficient male flowers results in poor pollination and development
of deformed fruits that lack an aril. Silengkeng, a cultivar originally from Indonesia, will naturally produce more male flowers than other cultivars and has a prolonged anthesis period that can extend over 4 months. These 2 characteristics make it a good pollinator tree for orchards. Maturation of terminal shoots is non-synchronous in Hawaii, therefore maturation of terminals does not often coincide with the onset of water stress periods. Vegetative flushing can occur in response to a significant amount of rainfall, harvest, or pruning. Flushing typically occurs 3-4 times yearly with pronounced flushing in May and smaller flushes in August and November. The presence of heavy fruit set can reduce flushing and negate the effect of rainfall. Little flushing occurs during winter months even in the presence of high precipitation.
Impacts
Flowering of rambutan trees in Hawaii occurs on mature terminals approximately 1-2 months after a period of water stress. Flowering is split between the two induction periods and can occur in spring (April to May) or in summer (July to August) which is the principal flowering period. Harvesting occurs at 16 to 20 weeks after anthesis, and at harvest BRIX for the aril is 18% or greater. Hawaii has 2 harvest seasons. The main harvest season is in winter between December and January with a second minor harvest season in late-summer (August to September). Two harvest seasons will enable Hawaii producers to market fruits during summer and during winter when rambutan from Southeast Asian producers are not available. Flowering panicles on rambutan cultivars planted in Hawaii possess mostly hermaphroditic functionally female flowers with a very small percentage (<1.0%) of hermaphroditic functionally male flowers. Anthers on hermaphroditic male flowers dehisce and shed pollen,
but the absence of sufficient male flowers results in poor pollination and development of deformed fruits that lack an aril. To overcome this problem, Silengkeng, an Indonesian cultivar, should be inter-planted in the orchard since it naturally produces more male flowers than other cultivars and has an anthesis period that can extend over 4 months. These characteristics make Silengkeng a good pollinator tree for Hawaii orchards. Maturation of terminal shoots is non-synchronous in Hawaii, therefore maturation of terminals does not often coincide with the onset of water stress periods.
Publications
- No publications reported this period
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Progress 10/01/03 to 09/30/04
Outputs
Rambutan cultivars responsive to the potassium salt of naphthalene acetic acid (K+NAA) were identified, by treating cultivars (Binjai, Jitlee, R162, R167, R9, R134, R137 Red, R156 Red, Rongrien, R7, and R156 Yellow) with 90 ppm of K+NAA between June and September. Cultivars were located in East Hawaii and situated on rocky Aa to silty clay loam soils and elevations between 75 to 250 m. Panicles were sprayed to runoff with K+NAA when approximately 10% of the flowers were at anthesis. All cultivars responded to 90 ppm K+NAA. Male flower production was apparent 4 to 5 days after treatment. Maximum numbers of male flowers were produced at 6 to 8 days, and production ceased after about 12 days. Rongrien and Jitlee consistently produced male flowers, and anthesis occurred more synchronously than with other cultivars. Although Binjai, R162, and R156 Red were very responsive to K+NAA, low numbers of male flowers were produced if panicles were not treated during the peak
flowering period. Little or no male flowers were produced on untreated panicles for all cultivars. Cultivars, R156 Yellow, R134, and Silengkeng seemed to produce a low number of male flowers without NAA treatment. The effect of timing of application of the K+NAA sprays was determined by treating panicles at an advanced stage of anthesis. Jitlee panicles were treated with 90 ppm when approximately 50% of the flowers had completed anthesis. These panicles treated produced male flowers at 4 days after treatment. Male flower production peaked at 6 to 8 days and gradually ceased after about 12 days. Multiple applications of K+NAA to individual panicles were also studied on Binjai and Jitlee. Panicles were treated at 10% anthesis with 90 ppm and retreated with the same concentration 8 days after the first application when approximately 50% of the flowers had opened. The data showed that male flower production peaked about 9 days after the first treatment, and their production ceased about 7
days after the second treatment, or 15 days after the first spray application. There was a slight increase in the average number of male flowers per panicle on the twelfth day after treatment when the data were compared to data from panicles sprayed once at 10% or at 50% anthesis. These results indicate that a second application of 90 ppm K+NAA prolonged the formation of male flowers by approximately 3 days. Viability of pollen grains from NAA induced male flowers was determined with a pollen germination medium containing , 50 ppm H3BO3, 150 ppm Ca(NO3)2 4H2O, 100 ppm MgSO4 7H2O, 50 ppm KNO3 and 5% Sucrose. Pollen grains from 11 cultivars were tested for viability along with pollen from naturally produced male flowers of Silengkeng and pollen from flowers of a male tree. Pollen from NAA induced male flowers from the 11 treated cultivars, the Silengkeng pollen, and pollen from the male tree successfully germinated within 15-42 hours after incubation in the germination medium. Results
of the germination tests confirm that induced and non-induced male flowers are able to produce viable pollen for pollination.
Impacts
Rambutan cultivars responsive to the potassium salt of naphthaleneacetic acid (K+NAA) were identified. Cultivars (Binjai, Jitlee, R162, R167, R9, R134, R137 Red, R156 Red, Rongrien, R7, and R156 Yellow) in East Hawaii orchards on rocky Aa to silty clay loam soils and between 75 to 250 m elevation were treated with 90 ppm K+NAA. Panicles were sprayed to wetness when approximately 10% of the flowers were at anthesis. All cultivars responded to K+NAA. Maximum numbers of male flowers were produced 6 to 8 days after treatment and induction ceased after about 12 days. Little or no male flowers were produced on untreated panicles, except for R156 Yellow, R134, and Silengkeng which appeared to naturally produce male flowers. To determine if K+NAA was successful in inducing male flowers when panicles were at an advanced stage of anthesis, Jitlee panicles were treated when approximately 50% of the flowers had initiated or completed anthesis. Male flowers were visible in about 4
days. Production of male flowers peaked 6 to 8 days after the treatment and gradually ceased after about 12 days. The effects of multiple applications of K+NAA to individual panicles were also studied on Binjai and Jitlee. Panicles were treated at 10% open and retreated 8 days later when approximately 50% of the flowers were open. The number of male flowers peaked about 9 days after the first treatment and ceased about 7 days after the second treatment, or 15 days after the first spray. These results show that a second application of 90 ppm K+NAA can prolong development of male flowers by approximately 3 days.
Publications
- Nagao, M.A., Tsumura, T. and Kawabata, A.M. 2003. Update of tropical fruit crop research in Hawaii. Proceedings of the 13th Annual International Tropical Fruit Conference. 12 p.
- Nagao, M.A., Leite, H.M., Hara, A.H. and Niino-Duponte, R.Y. 2003. Mangosteen caterpillar. Proceedings of the 13th Annual International Tropical Fruit Conference. 2 p.
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Progress 10/01/02 to 09/30/03
Outputs
Previously we demonstrated that fruit set of rambutan in Hawaii is often limited by the absence of male flowers within the orchard and sufficient pollen to obtain good fruit set and normal fruit development. We also demonstrated that the acid form of naphthaleneacetic acid (NAA) could stimulate the development of male flowers when applied at a specific period during flower development. Although very effective, in the acid form NAA is difficult to use due to its insolubility in water. A series of experiments were conducted to determine whether the potassium salt of NAA (K+NAA), which is highly soluble in water, could be as effective as the acid form for stimulating male flower development. The potassium salt of NAA is the active compound in plant growth regulators such as K-Salt Fruit Fix which is registered and used to control preharvest drop of apples and pears and for thinning of apples, olives, citrus and pears. To determine the optimum concentration of K+NAA
required for development of male flowers, rambutan panicles on Jitlee and 156 Red trees were sprayed to wetness with 0, 45, 90, 135 or 180 ppm solutions when approximately 10% of the flowers on each panicle were at anthesis. Data at 7 days after treatment showed that the 90 ppm concentration produced the best result. Additional tests showed that Jitlee and Binjai developed up to 50 male flowers/panicle at 6-7 days after panicles were treated with 90 ppm K+NAA. Observations also revealed that panicles with a more robust appearance were more responsive to NAA and that individual flowers responding to the K+NAA were those where the tip of the flower was beginning to open and the white tip of the pistil was just visible. Flowers that were entirely closed and those with a fully exposed stigma were not responsive. These results show that 90 ppm NAA can be effective in stimulating the production of male flowers within 7 days after treatment and that only flowers at a specific stage of
development are responsive to NAA.
Impacts
Experiments determined that the potassium salt of NAA (K+NAA), which is highly soluble in water, could be as effective as the acid form for stimulating male flower development in rambutan. The potassium salt of NAA is the active compound in plant growth regulators such as K-Salt Fruit Fix which is registered and used in bearing apples and pears, olives, and citrus and pear trees. The optimum concentration of K+NAA required for development of male rambutan flowers at 7 days after treatment was a 90 ppm concentration. Tests showed that varieties such as Jitlee and Binjai developed up to 50 male flowers/panicle at 6-7 days after panicles were treated with 90 ppm K+NAA. Panicles with a more robust appearance were more responsive and flowers responding to the K+NAA were those where the tip of the flower was beginning to open and the white tip of the pistil was just visible. Flowers that were entirely closed and those with a fully exposed stigma were not responsive. Since
maximum production of male flowers occurs about 7 days after treatment, multiple applications on different panicles within an orchard will be necessary to insure that male flowers are present throughout the flowering season and to insure good pollination and fruit set.
Publications
- Nagao, M.A., Leite, H.M., Hara, A.H., Kawabata, A.M., Terada, A.Y., Salakpetch, S. and Chandraparnik, S. 2002. Abstract: Update of tropical fruit crop research. Proceedings of the Twelfth Annual International. Tropical Fruit Conference.
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Progress 10/01/01 to 09/30/02
Outputs
No progress to report. This project was initiated on October 1, 2002.
Impacts
(N/A)
Publications
- No publications reported this period
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