Fruiting the mangosteen at an early age is an attractive concept which has occupied the minds of researchers and enthusiasts alike for many decades. Over recent years in north Queensland evidence has accumulated to indicate that by grafting terminal scions from fruiting trees (or their previous asexual propagules) then some crop may be obtained within the subsequent 7 year period. One or two fruit may even be achieved in the first year if scions have initiated flower buds prior to grafting. However evidence is equally strong to suggest that growth rates of grafted trees are so slow, trees so unthrifty, fruiting so irregular and fruits so reduced in size so as to make the practice uneconomic for commercial production.
There may however be some value in the grafted tree for home garden purposes - where a very small tree may be desirable. At this juncture only seedling trees should be considered for commercial orchards. However, the author would be quite happy to receive information which points to the contrary.
Philosophy of Clonal Grafting
For the majority of commercial fruit tree species it is virtually mandatory to graft, air layer or strike cuttings in order to perpetuate the individual fruit varietal characteristics. There are some exceptions with polyembryonic (true-to-type) seedling development in a number of species including - jaboticaba, mangosteen, mango and some citrus etc. Grafting also has additional benefits in increasing precocity (earlier fruiting), and generally reducing tree size, particularly when dwarfing rootstock are used. For most fruits, dwarfing is desirable in order to lower the bearing surface height and reduce costs of pruning, picking, pest and disease control etc. Yield per unit area is compensated for or even increased by planting at greater densities.
Due to the very slow growth rate of mangosteen, the search for rootstocks has been mainly concentrated on those species which are graft compatible and providing accelerated scion growth. Unfortunately, a great number of the garcinia and related species (including the three north Queensland species, Garcinia mestoni, G. warrenii and G. cherryi) have proved to be either graft incompatible, or, providing no benefits in terms of growth and precocity.
Garcini tinctoria, G. morella, G. livingstonei, G. benthami, G. dulcis and Clusia rosea have all been reported as compatible, but due to an apparent absence of use of these as rootstocks, one could assume that they have provided no benefits in real terms. Garcinia tinctoria has been shown to accelerate growth of container-grown mangosteen when used as a nurse rootstock in Florida, and there are some reports of G. xanthochymus being beneficial when used in this capacity in north Queensland. However the Kamerunga experience with G. xanthochymus suggests none, if not negative value.
Garcinia mangostana is graft-compatible with its own species and grafting is relatively simple, but obviously there is some growth restriction through the graft union giving rise to weak trees. This is not to suggest that rootstock research should not be further pursued. both by researchers and enthusiasts. For example, multiple inarched nurse roots (using G. mangostana) may be worth looking at.
Seedling Versus Grafted Mangosteen Performance.
Early reference to mangosteen seedling performance in north Queensland indicated that 12 to 21 years of growth was necessary before first fruiting occurred. However, changes in irrigation, mulching and fertilizing practices together with an understanding of shade relationships has proved that fruiting is achievable within 10 years from seed.
|Age from Seed|
|No. of Harvests|
|1||Seedling KHRS||10||3.8 m||10.9 m3||3/83||1|
|2||Seedling KHRS||10||3.8 m||9.7 m3||3/83||1|
|9||2.2 m||2.2 m3||Nil*||-|
|4||Seedling R. Ernst, Cairns||10||5.1 m||32.2 m3||/81||4|
|5||Seedlings C. Ong, Darwin|
|7 or 8||Mean 0.9 m||0.7 m3||11/82||1|
|6||Seedling H. Bosworth|
+ Tree volume is a measure of the canopy volume and is relative to the bearing surface capacity.
* Tree Fruited shortly after grafting but not since.
Problems associated with grafted trees are very much reduced growth, multiple suckering from rootstock in first two years, inability of some trees to maintain upright structure without staking, sparse and small-leafed foliage, reduced fruit size and irregular bearing.
It is evident that even with superior culture, a significant volume of fruit for picking would not be available until years 10 to 12 following field planting (assuming seedlings are planted out at 2 years of age). Thus investment replacement (net value of crop equalling establishment and maintenance costs, without even considering interest on investment) may not occur until years 16 to 20.
The fruit appeal is so universally acceptable that undoubtedly mangosteen would be a high-priced product on Australian markets. On the other hand, harvesting costs are likely to be substantial. The fruit are not easily located from outside the canopy and picking from inside is complicated by the multitude of close spaced branches. Quite a number of pickings are necessary for each of the two crops per year since individual fruit reach maturity over a protracted period.
Mechanical harvesting with a tree shaker and catching platform may however provide an answer.
The mangosteen will undoubtedly figure in horticultural production in North Queensland in the future but we have still a long way to go to realize its full potential. Cultural management research designed to improve growth rates, precocity and maximise yield should be the immediate aim.
DATE: September 1983
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