| dc.description.abstract | The objectives of the research were to determine the effect of
pathogen stem canker on the burnt rubber wood anatomy (Hevea
brasiliensis Muell. Arg.) included the causal agent, symptoms and rate of
wood decay. The research resulted that the canker occurred locally at the
area of fire injury directed from base to upright of the stem. Symptoms of
the canker were opened xylem, callus formation which could not fully
covered the xylem causing malformed stem, splitting, pelled and uneven
floem around the canker. The causal agent of the canker was a species of
white rot fungus belonged to the class Basidiomycetes. The fungus infected
the rubber wood and the hyphae could be found outside (intercellular) and
inside the woody cell cavity (intracellular). The hyphae infected through
pith, perforation side and degraded cell wall enzymatically. Response of the
tree against the fungus attack was deviation of wood in the form of callus
formation, inserted floem, smaller pores of xylem adjacent to the callus,
deviation of ray direction and formation of decay zone with abundant pores
filled with tylosis and gum, barrier zone consisted of pores filled with gum,
active and inactive cambium zones respectively showing an area of wood formation before and after fire. The lower rate of wood decay in transversal
section indicated the tree formed defense vessels to avoid expansion of the
fungus in other vessels. The characteristics of wood were also changed, i.e.
wood colors were changed from dark brown to light brown or pale and
whitish, wood textures were changed from smooth to rather rough till
extremely rough, fibre direction changed from straight till interlocked grain
to wavy, wood surface changed from medium to extremely rough and the
hardness of wood reduced till soft and rotten. The attack of fungus on
xylem formed before fire was not significantly affected the change of
dimension and number of cells. Significantly difference between xylem
infected by fungus before fire and xylem without infection after fire and
also xylem at the top of the tree caused by reaction of the tree in the effort
of covering injury at the canker area by forming callus and defense vessels
such as pores and axial parenchyma contained with gum to avoid expansion
of the fungus in order to distribute food to the whole parts of wood needed
for the growth of the tree continuously. From the results it can be
suggested that burnt rubber wood infected by fungus growing on the
unfertile area should be cut as soon as possible, because wood deterioration
will be extended when it is too long exposed to the opened area without
ability to cure naturally. Based on the anatomic structures of burnt rubber
wood infected by the fungus, it is indicated that the wood still usable,
however to determine how far are the value and utility, it is needed further
researches, mainly about the change of wood characteristics chemically,
physically and mechanically. Observations on the characteristics of the
fungus are needed to find out method of control. | en_US |
