by
M.R. Bowen and T.V. Eusebio1
This document, published within the framework of FAO/UNDP Project MAL/78/009, “Seed Source Establishment and Tree Improvement” 1, reports on recent information from Sabah, Malaysia on flowering and seed production and handling in plantationgrown Gmelina arborea. The following main subjects are discussed: Flowering; Fruit collection and handling; Fruit yields; and Seed germination.
The inflorescence in Gmelina arborea is a terminal dichasial cyme, with older flowers at the base of the panicle and the youngest ones at the tip. Many stages of bud and fruit development are found on the same inflorescence.
Because of the morphology of the flower, self-pollination is unlikely to occur in nature. However, in controlled pollination experiments in Sepilok, Sabah, self-pollinated flowers have produced full-sized fruits; it is not yet known whether the seed produced in this way is fertile or not.
Many types of flying insects seem to be active in the crowns of flowering trees in Sabah, suggesting that these insects may act as pollen vectors.
Studies on flowering indicate a general pattern of two peak periods for flower burst, which vary somewhat from year to year and depending on the location. The main production of mature fruits takes place approximately one month after the flowering peak, spreading over a 2-month period.
Harvesting mature drupes from the crowns is expensive, especially as branch lopping is not possible without destroying subsequent seedcrops. Fallen fruits are therefore collected from the ground, selecting those which are yellow-green in colour.
The pulp can be successfully removed from the nut by tumbling the fruits is a cement mixer together with cubes of hardwood, and sieving and washing the nuts clean of debris. Care must be taken to choose blocks of wood that are heavy enough to de-pulp the fleshy drupe, but not so heavy as to crack the nuts. Coffee de-pulping machines have also been successfully used to remove the pulp from Gmelina nuts2.
After de-pulping and cleaning, nuts are dried at +45°C in a specially constructed kiln for approximately 17 hours, to about 8% moisture content. Satisfactory drying can also be obtained using a commercial cocoa drier.
After drying, traces of residual pulp can be removed by tumbling the nuts in a cement mixer, or using a coffee de-husker which rotates the nuts against an abrasive surface. Complete removal of the pulp appears to be necessary for good germination of the seed. Seed can satisfactorily be stored at approx. +3°C when dried.
A small 14-year old plantation of Gmelina arborea was recently culled in Sabah, leaving 36 trees for seed production purposes (equivalent to a stocking rate of 96 trees per ha). During the first 6 months after thinning, a total of 201 kg of fruits, equivalent to 10.9 kg of dried nuts was collected from the stand. Monthly nut yields over the 6-month period in each of the 36 trees have been recorded and are reported in the document, showing a marked difference between trees in individual fruiting patterns.
Investigations have also been made into seed germination, with special reference to the comparatively low germination percentage found especially in imported seed.
Cracking open the nuts showed that, on an average, each nut contains 1.8 seeds of which 85% (1.5 seeds per nut) were assessed, on appearance, as being healthy and welldeveloped. Soaking the nuts in water at +25°C for 17 hours, followed by drying at +45°C for 7 hours, proved to be the pre-treatment which yielded the highest number of seedlings (88%). The experiments also showed that stored nuts (i.e. nuts dried to approx. 8% moisture content and subjected to temperatures of +3°C) germinated better than freshly collected nuts.
To check the results of the laboratory germination tests against those that may be expected under nursery conditions, pre-treated nuts were sown in seed boxes containing one of 12 different media consisting of sand, forest top soil and sawdust, either pure or in mixture. Of the 3 pure media, sawdust proved to be the least satisfactory and reduced germination whenever it was added to a mixture. The most effective media were those combining soil and sand, with 2 parts of soil and 1 part of sand being optimal for germination. However, subsequent radicle growth was best in mixtures containing sawdust, which apparently decreased the compaction of soil and thus favoured the development of a healthy root system.
