Abstract:
A major disadvantage in planting shade trees in
tea plantations is the favourable effect trees would have
on blister blight disease caused by ~~basidi~m vexans.
Massee. Presently, in Sri Lanka, tea is grown at the
higher elevations generally without shade. However, in
the future it m~ become necessary to plant trees on tea
e~tates to meet the needs of firewood and timber for the
tea industry as well a" for their beneficial effects on
tea. In this context it is important that sufficient
knowledge on the effects of trees on the disease be
obtained. Considerable data is available on Blister Blight
under unshaded field conditions. Very little work appears
to have been done, however, on Blister Blight under shaded
conditions.
The main objective of the present study was to
determine quantitatively the changes in infection of tea
plants by E.vexans ,brought about by the presence of tre.es
growing among them.
The effects of shade on the germination of spores
of E.ve~ deposited on the leaves of excised tea shoots
and the susceptibility of these shoots to infection by the .
.
pathogen were studied in laboratory experiments. The
.
. .
effects of shade trees on the incidence of Blister Blight
was studied in a statistically designed field experiment.
The germination of spores was found to increase
with increasing density of shade, and decrease with
increasing age of leaves. More appressoria were formed on
'sun leaves' than on 'shade leaves'.
In one method used to inoculate excised shoots with
~~~exans although germ tubes and appressoria were produced,
lesions were not obtained indicating the failure of
infection on excised shoots, perhaps due to changes in the
physiology of the leaf tissue following excision.
The incidence of Blister Blight as measured by .
4
infection on the third leaf was always higher on tea grown
under shade in the field experiment. Shade in tea generally
caused significantly more disease than unshaded tea provided
that infection in unshaded tea was more than 20%. When it
was less than 20% the differences in infection on tea with
and without shade trees was lese noticeable.
