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Agarwood is a resinous wood substance that is produced as a non-specific host response to
wounding, insects or microbial invasion by certain trees of family Thymelaeaceae. Most
species of Aquilaria and a few species of Gyrinops, Aetoxylon and Gonystylus are capable of
producing agarwood. Gyrinops walla is the only agarwood producing tree growing in Sri
Lanka which is believed to be endemic. Previous studies have identified that the two fungal
species Aspergillus niger and Fusarium soloni are capable of inducing agarwood formation in
G. walla. Since those fungi form toxins, it can be assumed that the agarwood production is
induced by fungal toxins. Although the ability of fungal species in agarwood production
inducement was studied previously, the impact of toxins on agarwood production was never
tested. Therefore the present study is aimed to investigate the ability of these mycotoxins to
induce the formation of agarwood in G. walla. Secondary metabolites were extracted from
one selected isolate of A. niger and F. soloni. The presence of toxins in those metabolites was
confirmed through a structured leaf bioassay. Volumes of 5 ml and 10 ml of extracted toxins
were inoculated into live healthy G. walla trees and the formation of agarwood resin within
the stem was observed using tissue samples collected at 10 cm above and below the
inoculation points, 3 months after inoculation. Agarwood resins were extracted from those
tissues and resin constituents were analysed by GC-FID method. According to the results,
tissue samples obtained from trees inoculated with toxins of F. solani showed higher average
resin content (1.69%±0.33) than the trees inoculated with toxins of A. niger (0.81%±0.26)
though there was no significant difference (F=2.34, p=0.099). The highest resin percentage
was observed with 5 ml inoculation of F. solani toxins (2.00%±0.82). Several resin
constituents considered as important markers in identifying agarwood aroma were present in
the resins extracted from inoculated trees. Among them, 6-acetyl-7-hydroxy-2,2-dimethyl
benzopyran showed the highest abundance. However, the presence of common resin
constituents was higher in the inoculation of toxins of A. niger when compared to toxins of F.
solani. This study identified that fungal toxins can be used as an effective inoculant to trigger
the formation of agarwood in G. walla. However, further research is recommended to verify
above observations.
