Inducement of Agarwood Resin Formation in Aquilaria crassna Using Three Endophytic Fungal Species

Abstract

Agarwood is a highly valuable fragrant resinous wood, formed in the stem, branches and roots of Aquilaria and Gyrinops genera of family Thymelaeaceae. Formation of agarwood mainly occurs due to infections, especially by fungal species. This study identified the potential of Aspergillus terreus, Fusarium equiseti and Trichoderma harzianum to induce agarwood resin formation in A. crassna. These fungal species were selected based on a previous study which identified 19 different fungal species from agarwood tissues of both A. crassna and G. walla. Hundred ml of spore suspension of each fungal species in potato dextrose broth was inoculated at two opposite points of A. crassna stems with three replicates. After four months of inoculation, these trees were cut and discoloured tissue samples were collected at 20 cm intervals above (+) and below (-) each inoculation point. Agarwood resin content was analysed by solvent extraction and constituents were identified by GC-FID method. Munsell soil colour chart was used to record tissue and resin colour. According to the results, the colour of tissues formed at inoculation point due to A. terreus, F. equiseti and T. harzianum were brown, dark brown and strong brown respectively. The colour of the oils formed by the above three fungi were pale yellow, olive yellow and yellow respectively. The tone of the colours faded when the distance increased from the inoculation point. F. equiseti caused the highest length of agarwood formation (+10.40, -8.70 cm). The formations caused by A. terreus and T. harzianum were +6.10, -5.60 cm and as +4.10, -3.90 cm respectively. Width of formation at the inoculation point were 5.40, 4. 50 and 7.10 cm for A. terreus, F. equiseti and T. harzianum respectively. The average oil contents formed by above species were 1.52%, 1.38% and 2.43% respectively. GC analysis revealed nine key compounds of five classes in oils formed by A. terreus. There were five compounds of four classes for F. equiseti and eight compounds of five classes for T. harzianum. Among them agarofuran, agarospirol, valecane, vetispirane, guaiene, eremophilane, selinene and fatty acids were the most common compounds identified in the oil formed by all three fungal species. The results confirmed that the percentages of resin content and constituents were higher due to T. harzianum than the other two species.