Research for the development of sago palm (Metroxylon sagu Rottb.) cultivation in Sarawak, Malaysia
General introduction (Chapter 1)
This chapter contains an overview of knowledge with respect to the cultivation of the true sago palm (Metroxylon sagu). The palm flowers once and forms suckers or tillers. Seedlings grow into a rosette stage of leaves and trunks are only formed after 4-6 years. The trunk may reach a length of 6-14 m and possess a trunk of 7-24 feathered leaves. An enormous inflorescence heralds the end of the life cycle. Formation of the inflorescence, for which the starch in the trunk is being used, begins 4-14 years after the start of trunk formation.
Continuous suckering multiplies the palm vegetatively, forming a cluster around the leader palm. Suckers are commonly used for vegetative propagation by man. Since time immemorial, man uses the sago palm trunk as a source of food starch in South East Asia. It has been a commercial crop of smallholder farmers on peat soils in Sarawak for a long time. At present, Sarawak exports nearly 50,000 tonnes air-dried sago palm starch.
Since 1982, the Sarawak Government tries to improve and increase its cultivation, as it is one of the few crops that can be grown with reasonable success on the rather wet deep peat soils. For this purpose, a research station has been established at Sungai Talau Station and a laboratory in Mukah. The semi-govern mental agency for land development, Land Custody and Development Authority, is planting sago on some ten thousands of hectares, in order to develop part of the 1.5 million ha of poorly drained peat soils.
The chapter ends with an overview of the main limiting factors for sago palm cultivation. This lead to the research presented in this thesis.
Factors affecting the subsequent survival rate of sago palm suckers in the nursery (Chapter 2).
Suckers are the most popularly used planting material for establishing sago palms in smallholder gardens and plantations in Sarawak. In nurseries, the mortality rate of suckers is around 20-40%. In the dry season, higher mortality rates are common.
Factors suspected to affect the subsequent survival rate of sago palm suckers in nurseries were investigated. The survival of suckers was significantly enhanced if they were planted promptly, best if it was within three days after removal from the parent palm. Suckers stored for more than two weeks before planting generally showed a marked decrease in their subsequent survival in the nursery. When the cutends and the whole or part of the rhizome were completely buried in the soil, an increased rate of survival was also obtained. Rhizomes planted 8 cm below the soil surface or just placed on top of the soil surface had lower survival rates. Trimming of roots to as short as 1 em did not affect the subsequent survival of the suckers. Trimming of the rhizomes to a length close to the growing point of the sucker was deleterious. Shading of suckers during the dry season appeared to contribute positively to their successful establishment.
When planting of suckers was delayed, treatment with a wide-spectrum fungicide while storing the suckers in cool and moist places was shown to reduce their mortality rate.
Effects of sucker size on the establishment of sago palms (Chapter 3).
The effects of sucker size on their subsequent establishment were investigated. Suckers of all sizes from 5 to 25 em in base diameter were established successfully without mortality. In general, larger suckers of 15-25 em in base diameter are faster in their establishment. However, these suckers are heavy, bulky, less abundant, and expensive to handle. In large- scale cultivation of sago palms, the use of large suckers has to be weighed in financial terms and availability of the material. It appears that larger suckers may be suitable for smallholder cultivation. In plantations, smaller suckers of 7-10 em in base diameter are recommended.
Effects of plant spacing on the growth and development of sago palms on undrained deep peat (Chapter 4).
The growth of sago palms was compared at 4.5 m, 7.5 m, 10.5 m and 13.5 m square planting. Palms spaced at 4.5 m had the lowest frond emergence rate, smallest trunk circumference at the base and at 1 m above ground level (a.g.l.), shortest prostrate (ground)trunk, longest fronds with thinnest rachides and the smallest crown size. They produced the least numbers of trunks and suckers, and their canopy was closed before trunk formation commenced in the third to fourth year after field planting.
The vegetative growth was intermediate in the 7.5 m spacing treatment. Compared to 4.5 m spacing, these palms had significantly higher frond emergence rate, larger crown size and trunk circumference, better stem formation and suckering ability as well as shorter fronds with thicker rachides. Their canopy was closed by the fifth to sixth year after planting. However, when compared to the 10.5 m and 13.5 m spacing treatments, the 7.5 m treatment palms had significantly smaller crown size, lower frond production rate, longer fronds and thicker rachides, smaller trunks at 1 m a.g.l. and slower trunk formation. There were no differences among these treatments in the suckering ability and the size of the basal circumference of the trunk.
Significant differences between spacing treatments of 10.5 m and 13.5 m were only found in the frond length, sucker number and frond production rate. However, the canopy of palms spaced at 10.5 m was about to close in the eighth year whereas those spaced at 13.5 m remained open. No difference was found in the average trunk height between any two spacing treatments.
The formation and growth of sago palm trunks were suppressed at 4.5 and 7.5 m spacing whereas at a spacing of 13.5 m, the field was under-utilized. Among the spacing treatments, the maximum trunk production per unit area was from palms spaced at 10.5 m. This suggests that sago palm on peat should be cultivated at a spacing of about 10 m.
Distribution and variation in the starch and moisture contents of sago palms at different growth stages (Chapter 5).
Sago palms of similar growth stages established on shallow peat vary in length, circumference and weight of their trunks. From the time of planting, a sago palm remains in the rosette growth stage for about 5.5 years before trunks are formed. Flower initiation occurs at 12.5 years and the fruit drop is completed in 14.5 years.
The average content and density of dry starch increases with increasing maturity of the sago palm until flowering. Maximum starch content of 18-20% is found between the full trunk growth stage (just before the emergence of inflorescence structure) and flowering stage. Thereafter, the starch content decreases sharply and remains finally at about 4 - 6%.
The moisture content is high and remains rather constant along the trunk of young sago palms. As the palm matures, moisture content decreases, especially in the lower portion of the trunk.
The lowest mean moisture content is found in palms from the full trunk growth stage to flowering stage, corresponding to the highest starch content in the trunk. In young and over- mature palms, the mean moisture content is higher. A high negative correlation (r2 = -0.85) is found between moisture and starch contents, showing the mutual replacement of starch and moisture in the trunk.
Within each growth stage, the density of the fresh trunk is constant along the entire trunk length. However, among different growth stages, the mean density of the sago palm trunk increases gradually from the early trunk formation stage. It reaches a maximum between the full trunk growth and flowering stage before decreasing in the subsequent over-mature stages.
This study provides an understanding of the pattern of starch accumulation and the relationship between the fresh density of the trunk and the starch content in it. This enables the harvesting of palms at the correct growth stage for maximum starch yield per unit time, and facilitates the grading of sago logs for starch yield based on their buoyancy.
Flowering biology of the sago palm (Chapter 6).
Scaffolds were constructed below the gigantic inflorescence of sago palms to investigate the flowering biology. In the early stage of development, flower buds occur in pairs in a bracteole. One is a staminate (male) and the other a hermaphrodite (perfect) flower. During development, abortion of either the staminate or the hermaphrodite flower buds occurs. By anthesis, mainly single flower buds are left in each bracteole. The sago palm is andromonoecious as indicated by the presence of staminate and hermaphrodite flowers in the same inflorescence. In three of the seven palms investigated, abnormal hermaphrodite flowers which opened prematurely were encountered.
The duration of flower opening in the entire inflorescence is about 30 days for the staminate flowers and 50 days for the hermaphrodite flowers. For the abnormal hermaphrodite flowers, opening may stretch over a period of three months and the premature stamens die during the opening. The peak of daily flower opening is between 1100-1400 hours. To a large extent, the sago palm is protandrous but overlaps in the opening of staminate and hermaphrodite flowers do occur. Seedless fruits are formed in all these palms. Visiting insects ( predominantly Trigona itama, Trigona apicalis and Apis dorsata) are found in great numbers during anthesis. However, only seedless fruits develop in most palms. This suggests that the pollen and pistil of sago palms may be self - incompatible. Bagging experiments to exclude visiting insects suggest that cross- pollination is obligatory in sago palms.
.In the current investigation, each sago palm produced between 276,000-864,000 mature flower buds and 2174-6675 mature fruits. The duration of fruit growth from anthesis to last fruit drop is between 19-23 months.
Germination of sago palm seeds (Chapter 7 ).
Some practical methods to increase the germination rate of sago palm seeds were investigated. The capability of seeds to germinate was found to increase as seed maturity advanced. Germination tests conducted on mature sago palm seeds using wet sand tray showed that removal of the husk and husk plus fleshy tissue (sarcotesta) enhanced germination. Loosening of the operculum and treatment with 10' M gibberellin also increased the number and speed of germination. Brief treatment with concentrated sulphuric acid was found fatal to the seeds. Germination of the entire sago palm fruit required an environment with high humidity. An easy and effective way of achieving this is to put mature sago palm fruits in partially permeable Hessian sacks placed in a damp atmosphere.
General conclusions (Chapter 8)
In this chapter, an assessment of the research results for practical application in sago cultivation is given.
Application of the findings from experiments on the survival of suckers may lead to an increase of survival between 10 and 40%. At the current cost of about RM 3.50 per sucker, this will decrease cost of planting, at the present planting distance, between RM 72 and RM 290 per hectare. Selecting suckers with a base diameter between 7 and 10 cm and a weight between 2 and 5 kg can reduce transportation and handling costs. This may also prevent price increase due to temporary sucker shortage when larger planting materials are preferred . Planting sago palms in a 10 m square pattern, with possibly a temporary plant in the middle of the square for oneharvest trunk , appears optimal for ultimate production. Findings in the distribution of starch in the trunk at different growth stages leads to harvesting just before flowering. Based on the ralation found between starch content, moisture content and trunk density, it may lead to the development of a practical method to estimate the starch content of a trunk based on its buoyancy. The results obtained in flowering and seed germination appear to be important and may be used for future breeding and research programmes. Sago palm seeds may also be used for new planting if suckers are either too expensive or in short supply.
The most pressing problems that needs attension in sago research is fertilizer application on the notoriously poor and badly drained peat soils. It is also important to start research on shortening the unproductive phase of the cultivation.