Rambutan (Nephelium lappaceum) Grafting Experiments

Horticultural Researcher, University of Puerto Rico brbrunner@yahoo.com

The rambutan (Nephelium lappaceum) is a fruit native to Malaysia and Indonesia. The name rambutan is derived from the Malay word for hair, and refers to the external hairlike spinterns on the fruit. World production is concentrated in Southeast Asia, primarily Thailand, Indonesia, Malaysia, Singapore and the Philippines (Laksmi et al., 1987), but production data is not readily available. Rambutan fruits are consumed fresh as well as canned, and are exported throughout the world either as fresh fruit, or in frozen or processed form. In recent years, rambutan plantings have been established in Australia, Hawaii, and in other regions outside the major areas of production as a specialty tropical fruit crop (Landrigan et al., 1996; Follett and Sanxter, 2000).

Rambutan in Puerto Rico

Despite the popularity of the quenepa (Melicoccus bijugatus) in Puerto Rico, other members of the Sapindaceae family, such as lychee, longan, and rambutan, are virtually unknown. Experience in Puerto Rico with lychee and longan, although rather limited, has shown these crops to be somewhat unreliable producers in our tropical environment. Rambutan, being more adapted to the tropics, may prove more successful.

Although records indicate that individual trees have existed in Puerto Rico since the 1920's (Britton and Wilson, 1923), recently there has been increasing interest in rambutan as a new specialty fruit crop for the island. The first commercial planting of rambutan, a 10 acre orchard in Mayaguez, was established in 1998. In 1999, experimental rambutan plantings were established at Experiment Stations in Corozal and Isabela, in a joint effort between the USDA Tropical Agriculture Research Station and the University of Puerto Rico Agricultural Experiment Station. As these orchards come into production, interest in the fruit and demand for planting material should increase. Currently there is no source of clonal planting material in Puerto Rico, and grafted or air layered trees must be imported from Hawaii at considerable expense. Although the Hawaiian trees are of excellent quality, serious losses of bare root trees have occurred in shipping due to delays and other problems. Thus, it would be desirable to have a local source of clonally propagated material for rambutan orchard establishment.

Rambutan Propagation

Rambutan may be propagated by seed, air layers, or grafting. Seeds lose viability rapidly if allowed to dry out, but may be kept in good condition for about a month if stored in damp sphagnum moss or sawdust. Disadvantages of seed propagated trees are delayed bearing, variable fruit quality and productivity, and unproductive male trees. Thus, seedling trees are used primarily as rootstocks for grafting, and not for orchard establishment.

Air layering is a common propagation method for the rambutan relatives, lychee and longan. Although rambutan has been reported to be difficult to propagate by air layering (Whitehead, 1959; Morton, 1987), air layered trees of desirable cultivars are commercially available (for example, see http://www.fruitlovers.com/new.html). One concern with air layered trees is their lack of an extensive root system and increased susceptibility to being uprooted by high winds or hurricanes (Galýn Saúco and Menini, 1984; Crane et al., 1994). I observed this on my own farm in 1998, after Hurricane Georges passed over Puerto Rico. Seedling lychees remained standing after experiencing hurricane force winds and over 20 inches (508 mm) of rain, while virtually all of the air layered trees were uprooted.

Various grafting methods for rambutan have been attempted in Puerto Rico with little success (M. Pérez, 2000, personal communication). Few references on rambutan grafting are available, and some of the information is conflicting. Therefore, I wanted to compare several grafting methods for success under local conditions.

Approach grafting, while more time consuming and complicated than other methods, has been reported to be very successful for rambutan (Morton, 1987; Sahadevan, 1987). The simpler methods of cleft and side veneer grafting were described by Morton (1987) as "not too satisfactory".

Various budding techniques have been reported to be successful in rambutan. According to Whitehead (1959), while shield bud grafts are "not feasible", modified Forkert budding is very effective. Morton (1987) describes patch budding with a success rate of 82 to 84%, however this method is somewhat difficult, as the patch must be cut for a precise fit in the stock. Sahadevan (1987) and Zee (1993) report bud grafting to be successful in rambutan, but don't specify the type of bud graft used.

Grafting Experiments

In the present study, I report results of six separate experiments comparing approach and cleft grafting methods in rambutan. Grafting attempts using budding were unsuccessful, and are not reported. The rootstocks used in these experiments were seedling trees grown in plastic bags under 50% shade, or, in the case of topworked trees in the field, were 5 year old seedling trees growing in full sun. The rootstock seed source was a freestone type of rambutan obtained from Río Guaycuyacu Farm (http://www.ecuadorexplorer.com/guaycuyacu) and sown on 28 September 1999. The trees used for rootstocks were about 3 feet (1 meter) tall, with a stem diameter about the thickness of a pencil. All grafts were wrapped with green plastic grafting tape, which was removed five to seven weeks later, after success or failure of the graft was evident. Cleft grafts in the field were wrapped first with grafting tape, then the entire scion was covered with Parafilm.

The procedures and results of the individual rambutan grafting experiments are summarized in Table 1. In the first experiment, seedling rootstocks growing in bags were moved to the field, and approach grafted with established trees of 'R-167' and 'R-162' rambutan.

This method was highly successful (100%), however, it is cumbersome because the seedlings must be securely placed around the mother tree, and must be watered if rainfall is insufficient. Also, the number of grafts that may be done at a given time is limited by space and available shoots.

The second experiment was with cleft grafting in the shadehouse. In this experiment, scions were left with three to five leaflets, and the plastic bags covering the grafts were left slightly open. These two factors probably contributed to drying and death of the scions, resulting in the low success rate of 10%.

Experiment 3 also utilized approach grafting, but this time the donor plants were young grafted trees in bags, and the grafting was done in the shadehouse. An inverted cleft type graft was used, in which the shoot of the root stock is severed, and the remaining stub cut to form an inverted 'v'. This 'v' is inserted into a vertical cut in the scion, and the graft is wrapped with grafting tape. This method is virtually foolproof, as the scion is allowed to heal before being removed from the donor plant, and is much easier to do in the shadehouse than in the field. The success rate in this experiment was 88%.

The fourth experiment attempted to correct some of the errors of Experiment 2. This time, all leaves were removed from the scions, and the plastic bags were completely sealed to prevent desiccation. After 2 weeks, some scions began to get moldy, so at 3 weeks, 1 inch (2.5 cm) breather holes were cut into each bag to reduce humidity. At 5 weeks, the bags were removed.

The changes in technique designed to reduce drying of the scion probably contributed to the improved success rate of 26%.

Experiment 5 attempted to improve on the success rate of the previous experiment by providing ventilation earlier (2 weeks after grafting) to prevent mold growth. Breather holes were also smaller, to avoid desiccation. However, the success rate did not improve with these modifications, but remained about the same (23%).

Cleft grafts in the field (topworking established trees) were more successful than in the shadehouse on seedling rootstocks (42% success rate). This could be due to the fact that the larger trees contribute to more rapid and efficient healing of the graft union, or that increased temperatures under full sun conditions improve the healing process.

Conclusions

Based on the results of these preliminary experiments, the method of approach grafting is more dependable than cleft grafting for clonal propagation of desirable varieties in rambutan. Although it is a more cumbersome method than cleft grafting, the high success rate justifies the extra time and effort involved, especially when the donor plants are in pots or bags in a shadehouse instead of large trees in the field. It must be kept in mind that the sample sizes I worked with are small, and the experiments were done at different times of the year, which can affect grafting success.

Apparently, moisture loss of the scion, before the graft wound has healed sufficiently, contributes to graft failure. Covering the graft with a sealed plastic bag improved the success rate, but mold tended to form on the scions. Other methods to prevent water loss need to be tried, such as the use of Parafilm or intermittent mist. The use of Parafilm instead of plastic bags, and increasing the light levels may improve grafting success in the shadehouse. In future experiments, I plan to examine the use of different types of bud and side veneer grafts.

References

Britton, N.L. and P.Wilson. 1923. Scientific survey of Porto Rico and the Virgin Islands. New York Academy of Sciences, New York.

Crane, J., C. Balerdi, R. Campbell, C. Campbell and S. Goldweber. 1994. Managing fruit orchards to minimize hurricane damage. HortTechnology 4:21-27.

Follett, P.A. and S.S. Sanxter. 2000. Comparison of rambutan quality after hot forced-air and irradiation quarantine treatments. HortScience 35:1315-1318.

Galýn Saúco, V. and U.G. Menini. 1984. Litchi cultivation. FAO Plant Production and Protection Paper No. 83, Food and Agriculture Organization, Rome.

Laksmi, L.D.S., P.F. Lam, D.B. Mendoza Jr., S. Kosiyachinda and P.C. Leong. 1987. Status of the rambutan industry in ASEAN. p. 1-8. In: P.F. Lam and S. Kosiyachinda (eds.) Rambutan: Fruit development, postharvest physiology and marketing in ASEAN. ASEAN Food Handling Bureau, Kuala Lumpur, Malaysia.

Landrigan, M., S.C. Morris and K.S. Gibb. 1996. Relative humidity influences postharvest browning in rambutan (Nephelium lappaceum L.). HortScience 31:417-418.

Morton, J.F. 1987. Fruits of warm climates. J.F. Morton, Miami.

Sahadevan, N. 1987. Greenfingers. Sahadevan Publications, Negeri Sembilan, Malaysia.

Whitehead, C. 1959. The rambutan, a description of the characteristics and potential of the more important varieties. Malayan Agric. J. 42:53-75.

Zee, F.T. 1993. Rambutan and pili nuts: Potential crops for Hawaii. p. 461-465. In: J. Janick and J.E. Simon (eds.) New crops. Proceedings of the 2nd National Symposium New Crops: Exploration, Research and Commercialization. 6-9 October 1991, Indianapolis, Indiana. Wiley, New York.

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