Abstract:
Gyrinops walla Gaertn. is the only species
growing in Sri Lanka that belongs to the agarwood family,
Thymelaeaceae. Although agarwood resin induction and
extraction from Aquilaria species of the same family have
been practised for many decades in Southeast Asian region,
the ability of producing agarwood resins in G. walla was
discovered recently. Since previous studies were on agarwood
resins formed due to natural causes, the present study
was conducted to identify the potential fungal species that
are capable of artificially inducing agarwood resin formation
in G. walla. Since this is the first ever study conducted
on artificial inducement of agarwood resin formation in G.
walla, Aspergillus niger and Fusarium solani were selected
owing to their high abundance in the naturally formed
agarwood resinous tissues collected from 25 G. walla trees.
Both fungal species were separately grown in yeast extract
glucose agar and used to inoculate healthy G. walla trees
under aseptic conditions. Three holes were made for each
tree and 2 g of fungal culture including the medium were
placed in each hole. Tissue discoloration, characteristic
aroma, resin content and resin constituents were checked at
10 cm intervals above and below the inoculation points for
a period of 1 year. Results revealed that tissue discoloration
and resin content were higher in the trees inoculated
with A. niger. Other than at 10 cm above and below
the inoculation points, samples collected at all locations
had significantly higher resin contents when inoculated
with A. niger compared to F. solani. Sixteen agarwood
resin constituents, which were also recorded in Aquilaria
species, were identified from the discolored tissues using
GC–MS analysis. Jinkohol, agarospirol and 2(2-phenyl)
chromone derivatives were found in all discolored tissues
collected at 10-cm intervals of the trees inoculated with
both fungi. b-Seline, c-eudesmol and valerenal were found
in nine of 10 sample points on the stem. c-Elemene was
recorded only in one sample. The characteristic aroma
during burning was stronger for dark-colored tissues than
the light-colored ones. The present study confirmed the
potential use of certain fungal species to induce agarwood
resin in G. walla and that A. niger is more effective than F.
solani