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Rubber, Natural 383

TABLE II Early Consumption that had been selected from trees known to be high in latex
of Natural Rubber yield.
Year Metric tons Selected seeds come from several sources: (1) natural,
random pollination of flowers of a high yielding tree, (2)
1825 30 natural cross-pollination between trees in the same clone,
1840 380 and (3) artificial cross-pollination of high yielding trees.
1850 1,500 The latter provides the best seedlings.
1860 2,700 Bud grafting was the next advance. A bud from a high-
1870 8,000 yielding tree is inserted under the bark of the lower stem
1880 13,000 of a young tree. If successful, the rest of the tree above
1890 23,000 the graft can be removed. The new branch then takes over,
1900 50,000 and becomes the main trunk of the mature tree. All trees
derived by vegetive reproduction from a single mother tree
are said to constitute a clone.
of a variable color, mostly light brown, but mottled with
The vast majority of plantation acreage has been re-
gray-green coloration. The tree can live for more than
planted with such high-yielding clones since 1945. These
100 years. The base circumference of the tree can be as
clones are less than two dozen in number. Typical names
much as 15 ft. However, most trees have a girth of 3 to
are Avros 49, Tjirandji 1, Bodjong Datar 5, Prang Besar
4 ft. Although the tree sheds its leaves once a year, latex
86, RRIM 501, RRIM 600, RRIM 703, etc. (Table III).
tapping can be continued. Normally, latex yields are lower
Currently, second and third generations of the RRIM 600
during the weathering season, usually about February. The
series have been yielding up to 6000 lb/year/acre in small,
fruit of the tree is a pod consisting of three sections, each
pilot-scale plantings.
with a seed. This is a characteristic of the Euphorbiaceae.
Young plants are raised in a nursery for the first year.
The trees are then planted in a permanent field in regular
B. Pathology (Diseases) rows about 14 to 20 ft apart. These are finally thinned out
until 100 to 150 trees are left per acre. Legumes, such as
Disease is a major enemy of the rubber tree. Yellow
soy bean plants, provide ground cover among the trees,
leaf blight has been mentioned. Brown bast, which
and also furnish fixed nitrogen for fertilizer. Phosphate
attacks the tree trunk, is a canker causing physiological
fertilizers are also used extensively.
disturbance. Oidium heveae is a fungus that attacks
the leaves. Corticium salmonicolor is another fungus
D. Tree Tapping and Collection
setting in the forks between branches. Phytophtora
paimivora thrives on the tapping panel. Fomes is a fungus The bark is the most important part of the rubber tree. It
resulting in moldy rot of the roots. It is small wonder is here that the latex vessels are found. These vessels are
that pathology is a major function of rubber research living cells, within whose walls the latex is found. La-
and production. Fortunately, there are known fungicides tex vessels are a network of capillary tubes that exist in
that are effective in preventing the spread of such all parts of the tree. In the trunk, these are vertical bun-
◦
diseases. dles inclined from right to left at about a 5 angle. These
bundles, arranged in a series of concentric rings, are con-
centrated near the cambium layer and are only 2–3mm
C. Planting and Cultivation
thick. The latex vessels are living cells that convert plant
The tree has a tap root that goes deeply into the ground, food materials into rubber hydrocarbon.
anchoring the tree against wind damage, providing food,
and resisting water drought. The most suitable soils are
TABLE III Yields by Decades
loamy, sandy clays, naturally drained, shade covered, and
rich in mineral nutrients and organic matter. Yield
In the past, Hevea trees were ready for tapping 5–6 years Decade Clone (lb/acre per year)
after planting. Recent research, however, has reduced the
1920 Unselected 500
period of immaturity to 3 or 4 years. Peak efficiency is
1930 Pil 384 1000
reached when the tree is almost 15 years old.
1940 PB 86 1200
Once the land has been cleared, young Hevea can be
1950 RRIM 501 1500
planted. The young plants are obtained by germinating
1960 RRIM 600 2300
seeds in a bed, then transplanting the young seedlings to
1970 RRIM 703 3300
a nursery. The early technique consisted of planting seeds