Phytochemical defenses of loblolly pine (Pinus taeda) in response to fungal symbionts of the southern pine beetle (Dendroctonus frontalis)

Southern pine beetle (Dendroctonus frontalis) (SPB) is the most detrimental pest of pine plantations and natural ecosystems in the southeast, capable of causing enormous losses. SPB has symbiotic relationships with three fungi, two nutritional mutualists, and one antagonist. Ceratocystiopsis ranaculosus and Entomocorticium sp. A, are mutualists, serving as a nutritional supplement for the SPB larvae. Meanwhile, the antagonist, Ophiostoma minus, competes for space and nutrients with SPB larvae and the two mutualistic fungi. There is evidence that direct competition may be a mechanism by which O. minus outcompetes the two mutualists, but other mechanisms may be involved. We hypothesize the plant defensive response to O. minus, a blue-stain fungus, induced in the host negatively impacts the mutualists more than itself, due to the mutualists not being plant pathogens and therefore not having evolved abilities to withstand tree defenses. The objectives of this study are: (i) determine the compounds induced in loblolly pine after inoculation of the three fungi, and (ii) in vitro testing of the compounds to determine effects on the fungi. We will inoculate all three of the SPB associated fungi into 50 trees within a loblolly stand in the University of Georgia’s Whitehall Forest (Athens, GA), in the Piedmont region. We will collect phloem samples before and three weeks after inoculation and measure the length of lesions three weeks post inoculation and analyze secondary metabolites. The results will assist in clarifying interactions within the SPB system and illustrate what defensive chemicals of loblolly are key against fungal infection.