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ABSTRACT |
Tea plants are classified
as Camellia sinensis variety sinensis and Canmellia sinensis variety
assamica (some trees more than 1500 years old are sill thriving in
their original forests in Yunnan Province, PRC). The tea plant is
kept as an evergreen shrub by pruning When hand picked, only the
leaf bud and first two leaves are plucked from the plant. Because of
increasing labor costs, mechanieal harvesting is now being used in
several countries. In tropical countries, tea leaves are harvested
all year around. In temperate countries, harvesting is seasonal.
In its
natural free-growing state, the tea tree can attain a height of
20-30 meters (m). Some trees which are said to be more than 1500
years old are still thriving in thriving flowers and fruits but very
few shoots suitable for processing to make tea. In the cultivation
of tea on a commercial basis, the height of the plant is maintained
at about 1 m for the convenience of manual harvesting of the tender
leaves. This control of the height is achieved by pruning at
intervals of 2-6 years according to prevailing climatic conditions.
In
1753, in the binomial system originated by Linnaeus, the tea plant
was classified as Thea sinensis. Many synonyms have been given, but
now it is generally accepted that the tea plant be classified in the
family. Theaceae and in the Camellia species. Many varieties have
been proposed, and there are many different qualities arising from
different cultivation practices and growing conditions. Camellia
sinensis, (L) O. Kuntze, is grown in a very wide range of lautudes,
from 45° N(Russia) to 30° (South Africa), and from 150° E (New
Guinea) to 60° W (Argentina). According to Sealy (1), there are two
main varieties, or jats, Camellia sinensis variety sinensis (Chinese
jat) and Camellia sinensis variety assamica (Assam jat). The
commercially grown tea plant is generally a highly heterogeneous
mixture with contributions from other species of Camellia, such as
C. irawadiensis and C. cambodiensis (2). Comprehensive accounts of
botany, botanical classification, and physiology of tea have been
provided by Barua (3) and Banerjee (4).
The tea plant is kept as an evergreen shrub by pruning. The leaves
are elliptical in shape, Figure I. 1. The flowers are white
with yellow anthers, similar to a wild rose. The tea fruit contains
three seeds. When hand picked, only the leaf bud and the first two
leaves are plucked from the plant. In some modern, large commercial
operations, a battery-powered miniature hedge clipper is used, and
the clipped material is collected in an attached bag, Figure I. 2.
In some very large operatins, tractor-mounted machinery is used in
harvesting tea leaves, Figure I. 3. In such mechanical harvesting
methods, more than the first two leaves are often harvested, in
contrast to the careful hand-plucking harvesting method.
In some
countries, as in the tropical countries, tea is harvested all around
the year. In temperate countries, such as Japan, harvesting is
seasonal and each year the new crop is highly prized.
Propagation of tea plants was originally by seed, and this added to
the heterogeneity. More recently (5) vegetative propagation methods
have been introduced and are now the accepted method for planting
new land and also for replanting or filling in vacancies in existing
tea land.
The
choice of the clone for vegetative propagation is dependent on
climatic conditions, tolerance to pests and diseases, and the nature
of the soil. Attempts are now being made to replace vegetative
propagation by tissue culture methods, but these investigations are
still in their infancy and it is difficult to predict what other
improvements will be developed. Tthere are several hundreds of
vegetatively propagated clones with varying characteristics, only a
few of which are suitable for commercial cultivation. The basis of
selection is by field trials trials to assess yield under different
climatic conditions and by evaluation of the quality of the tea
samples made from material processed from the field trial plants.
The annual yield of tea shoot tips is only 1-4 tons per hectare (ha)
and is much lower than the yields from vegetative crops such as
grassland, forests, and root crops, which yield 10-20 tons/ ha (6).
The net annual biomass production of tea plants is 15-18 tons/ ha
(7-9), which is comparatively lower than the 25-40 tons/ ha of other
vegetative crop plants. Various reasons have been advanced for the
lower productivity of tea plants, and among these are: canopy
architecture (10), link limitatin (11), and the partition of biomass
between woody stems and leaves. This partition of biomass results in
a low leaf harvest index of 11% in tea plants as compared with
30%-70% in grassland, forest, and root crop plants. Free-growing tea
plants have been observed (12) to produce 50% more dry matter than
pruned tea bushes and this may be as much as is produced by
grassland and forest species. The low tea harvest yield has been
discussed (6) and attributed to low photosynthtic efficiency and
partitioning of about half of the dry matter to the frame of the
bush, one quarter to the root system, and only 10% to the
harvested shoots, Table I. 1.
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