Agarwood is a dark, fragrant, valuable resinous wood produced in Aquilaria and Gyrinops tree species in the family Thymelaeaceae to protect internal tissues from microbial infections. Aspergillus niger and Fusarium solani are well known to induce agarwood resin formation. This study demonstrated for the first time that agarwood resin formation can be induced by the mycotoxins of A. niger and F. solani. Different volumes of mycotoxins extracted from the ASP-U strain (USJCC-0059) of A. niger and the FUS-U strain (USJCC-0060) of F. solani were inoculated into A. crassna trees at 1 m intervals. The impacts of the inoculations were observed through resin content and constituent analysis at 7 months after inoculation. Resin production due to the mycotoxins of ASP-U and FUS-U was restricted to ±20 cm and ±60 cm, respectively, from the inoculation point. Color of the resinous agarwood varied from yellowish-brown to black. The differences in resin content formation due to the different inoculant volumes of ASP-U and FUS-U were statistically significant, and the average resin contents varied from 0.89%-4.44% and 1.24%-9.20%, respectively. GC-MS analysis detected 27 constituents responsible for the characteristic aroma of agarwood resin. Among them, phenyl butanone, agarofuran, agarospirol, β-caryophyllene, alloaromadendrene oxide and (-)guaiene-1(10),11-diene-15-ol were found in all extracts. These are common in commercially available agarwood induced by fungal species. Hence, we demonstrated that the mycotoxins of specific fungal strains can be used for agarwood production. Therefore, chemically synthesized mycotoxins can be used at commercial-scale, eliminating the difficulties of maintaining live fungal cultures for agarwood production.

Agarwood, a highly valuable resin formed in the stems and roots of certain tree species of the family Thymlaeaceae can be induced the formation in artificial manner by using different fungal species. The potential of fungal toxins using certain strains of Aspergillus niger and Fusarium solani to form agarwood in Gyrinops walla, which is a native species to Sri Lanka, was identified in 2016. However, the potential of extracting fungal toxins in large scale was not studied previously for the purpose of inducing agarwood formation at commercial scale. Therefore selected strains of A. niger and F. solani were grown on Potato Dextrose Agar (PDA) medium and three agar plugs of A. niger were inoculated in Czapek Dox Broth (CDB) and F. solani in Yeast Extract Glucose Broth (YEGB). A 50, 100, 150, 200, 250, 300 and 500 ml series was prepared for CDB and YEGB to identify the potential impacts of different volumes of toxins. Mycotoxins were extracted after 14 days for A. niger and after 10 days for F. solani based on the results of a previous study. The impacts of those toxins were detected by a bioassay using A. crassna and G. walla leaves. A comparison was made using diameters of lesions caused by toxins in A. crassna and G. walla leaves after 48 hour. According to the results, the effects of toxins of F. solani and A. niger were not significant on A. crassna. Further the damage caused by F. solani (F=1.02; P=0.428) and A. niger (F=1.41; P=0.238) grown in different volumes was not statistically significant. However, the effect of toxins of F. solani was significantly higher than that of A. niger (F=10.69; P=0.000) on G. walla. Damage caused by toxins formed in different volumes of F. solani was not significant (F=1.81; P=0.103) on the leaves of both species. However, the damages caused by toxins A. niger grown in 50 ml and 100 ml were significantly lower on G. walla leaves than the rest of volumes. Based on these results, 500 ml can be used as an effective volume to extract toxins from A. niger and F. solani for inducing agarwood formation at commercial scale.