Survey of Volatile Organic Compounds Emitted by Four Ophiostomatoid Fungi
Type of DegreeMaster's Thesis
Forestry and Wildlife Science
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Loblolly pine (Pinus taeda L.) is an important commercial timber species in the southeastern United States. It contributes to the growth of the economy by serving as raw material for the forest product industry in the region and the entire United States. However, bark beetle vectored root infecting ophiostomatoid fungi: Grosmannia alacris, G. huntii, Leptographium terebrantis and L. procerum are threats to the growth and productivity of P. taeda. The ophiostomatoid fungi have been a major contributing factor of decline disease in loblolly pines. The interaction between beetle vectors and their fungi can be mediated by volatile organic compounds (VOCs) produced by the fungi, acting as communication cues which influences the behavior of plants and animals. Although VOC interactions between many organisms have been studied, ecological roles of VOCs from fungi remain largely unknown. The study investigated whether: (i) the fungal produced VOC profiles differed between species; (ii) the presence of a resource-sharing fungus affects the VOC production of a given fungal species; (iii) if seedlings inoculated with ophiostomatoid fungi (G. alacris, G. huntii, L. terebrantis, and L. procerum) produced VOCs that differed from controls. Volatiles were collected from G. alacris, G. huntii, L. terebrantis, and L. procerum in the lab and from seedlings inoculated with the four different fungi. Volatiles from seedlings were randomly and destructively sampled from the inoculation area at 4, 8 and 12 weeks after fungi inoculation. Volatiles were identified with gas chromatography – mass spectrometer (GC-MS). Eight compounds (ethyl acetate, isoamyl acetate, phenylethyl acetate (esters), isobutanol, 2-methyl-1-butanol, ethyl alcohol, phenylethyl alcohol (alcohols), and verbenone were identified and quantified from the ophiostomatoid fungi. Ophiostomatoid fungi can stimulate or inhibit the production of fungal VOCs in the presence of other fungi occupying the same ecological niche. Fungal VOC profiles were detected in higher concentrations when fungi were grown on the same culture plate, however, lower concentrations of compounds were recorded when fungi were grown on separate plate in the same chamber without touching each other. The compounds found in loblolly pine seedlings inoculated with ophiostomatoid fungi were identified as α-pinene, camphene, β-pinene, limonene, myrcene, terpineol, p-cymene, bornyl acetate, ocimene, γ-terpinene, trans-verbenol, 3-carene, camphene, cis-verbenol, and borneol. Loblolly pine seedlings produced monoterpenes after fungal inoculation, and the compounds increased until they peaked at week 8 and then declined during week 12. The results suggest that there are similarities in different fungal volatile organic compounds of species that occupy the same ecological niche, and the presence of different fungi can stimulate or inhibit the production of volatile organic compounds. The study also demonstrates that fungal volatile organic compounds can drive interactions between bark beetles and fungal symbionts. Also, the study showed that the compounds detected can be used to manage both bark beetle and its fungal symbiont.