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Tapping
Panel Dryness (TPD) is a phenomenon whereby some trees in
a field of nominally identical clones start to show reduced
yields which may eventually in some cases drop to zero. The
problem seems to be mainly associated with modern high-yielding
clones and there are a few such clones which are especially
prone to TPD which can cause the loss of as much as 10 per
cent of their potential production. It is still sometimes
known as brown bast.
Dr Jean Louis Jacob (CIRAD) considers that there are two
forms of TPD: (1) a chronic form and (2) an acute form.
The former is confined to the lactiferous system and does
not affect the phloem. It is caused by fatigue: senescence:
interaction disfunctioning (SOD). It is associated with
high intensity production and stimulation. The latter is
characterized by bark necrosis B the phloem is attacked.
The histological signs are a brownish manifestation and
there is extreme stress in the bark tissue. The twin forms
are quite distinct. The chronic form is related to latex
production, whereas the acute form can occur without latex
being produced. Moreover, unlike the chronic form where
the incidence appears to be random, the acute form tends
to affect a line of trees and is not random. The bark necrosis
form is disfunctioning and does not even need latex to be
in production. The chronic form is stress induced and can
be caused by drought, poor soil structure, aluminium poisoning
and wind damage. It is related to specific clone types and
their sensitivity to fatigue. The typology and dynamics
of clones with low sucrose contents needed to be studied.
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