Agarwood Resin Inducementin Gyrinops Walla: Beyond Fungal Inoculations

Abstract

Gyrinopswalla is the only natumlly gtou,ing agarwood producing tree species in Sri Lanka. It had no commercial recognition rutil its agarwood producing abiliry was scientifically identified n 2012. This paved avenues for numerous researches. This paper illuskates some studies conducted on differant inoculation methods using fungal species and their substances. The first attempt was made in 2014 to iderrtily the potential fungal species thar can be used at conrmercial scale for agarwood formation it G. v-alla. The inhabiting fungal species were identified frorn nafurally formed agalwood tissues G. w'allatrees of the wet zone of Sri Lanka. Those tissues were size teduced, sur{ace sterilised and placed in agar media to grow the inhabiting fungi which were then isolated and identified rvith colony and morphological characteristics. Altogether, 4 Fusarium, 4 Ttichodetma, 3 ,.lspergillus, 2 Botrytesp\1o"ria species and I species of each of Diplacladium, Mucor and Sarcinomyces were idelrtified. When re-inoculated as pule cultures, ,4. nigerand. F. solaniproduced the highest agarrvood resin contenrs (0.82+0.07% and 0.73+0.06% respectively) in G. v'allaup to 50 cm above the inoculation point in 6 rnonths. 16 and 15 key resin constituents were identitied from thoseresins formed by A. nigerandF. solanirespectively. Once 100 ml of spore suspensions of A. rigennd F. solaniin nutrient broth media were inoculated, the resin contents were 0.37+0.06Y, and 0.40*0.18% respectively after 4 months with pale yellow to brown in colour. Then potential of agarwood inducement using secondary metabolites was tested using different strains of the same fungal species. For this reason. the above t*'o tungal strains (ASP-U and FUSU) and tn'o other strains (ASP-N of .-1. nigerund FUS-N of l"-. solani) were grown in agar media and their secondary metabolites were extracted by tiitering through a series of ceramic filters of descending pore sizes. A bioassay conducted on G. wallaleaves confrrmed the toxicity of secondary metabolites only for ASP-U and FUS-U strains.Ther 50 ml of those were inoculated to {}. wallaatd. aflter 7 months, only ASP-U and FUS-U which wcre obtained tiom ihe natrually formed agarwood produced resins while the other two strairs were not productive . ASP-U produced resins (2.27+0.39%) only up to -20 cm fromthe inoculation point u,hile FUS-U produced resins (4.2t*0.47Yo) lp to *60 crn. The oi1 colour was yellou'with 14 key constituents and dark yellowish brown with 24 key constituents for ASP-U and FUS-U respectively. The results lead to assume that only some strains of the same firngal species are capable of inducing agarwood. Secondary metabolites of the effective fungal species can also be used tbr aganrood inducement which can be chemically manufactured at comme cial scale.