Isolation and reinoculation of a gall-inducing fungus in the invasive Brazilian peppertree (Schinus terebinthifolia) in Florida

Authors: Halbritter, Dale; RAYAMAJHI, MIN - Former ARS Employee; Madeira, Paul; Leidi, Jorge; TELMADARREHEI, TELMAH - University Of Florida; MINTEER, CAREY - University Of Florida

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2024
Publication Date: 4/18/2024
Citation: Halbritter, D.A., Rayamajhi, M.B., Madeira, P.T., Leidi, J.G., Telmadarrehei, T., Minteer, C. 2024. Isolation and reinoculation of a gall-inducing fungus in the invasive Brazilian peppertree (Schinus terebinthifolia) in Florida. Invasive Plant Science and Management. https://doi.org/10.1017/inp.2024.3.
DOI: https://doi.org/10.1017/inp.2024.3

Interpretive Summary: Galls are abnormal plant growths often caused by the infection of a microorganism and galls can divert nutrients within the plant. We have discovered that the plant we are trying to manage, Brazilian peppertree, using an insect biological control agent, a species of thrips, will occasionally have galls on its stems. The problem here is that we do not know whether the galls may impede the effectiveness of the biological control agent in the field or whether galled food plants will be less nutritious to thrips mass produced in the laboratory. The first step toward solving this problem is to determine the species of the microorganism responsible for the galls and to determine how to infect plants to conduct future experiments. We collected galls from wild plants and extracted the DNA to identify the species of microorganism within the infected plant tissue. It was identified as a species of fungus in the genus Cophinforma. We then demonstrated that the fungus can be isolated on a growth medium in a Petri dish and transferred to wounds on new plants. A new gall can form at the wound site in as little as 3 months. We confirmed the new galls were caused by the Cophinforma fungus via DNA evidence. We accomplished the identification of the microorganism and showed that new plants can be experimentally infected. This will contribute to solving the problem by allowing experiments to be conducted with the thrips agents feeding on infected and uninfected plants in controlled environments.

Technical Abstract: Stem galls and witch’s broom-like growths are locally abundant on the highly invasive Brazilian peppertree (Schinus terebinthifolia) at field sites in southern Florida where a thrips biological control agent (Pseudophilothrips ichini) is being released to reduce the invasive potential of the plant. Galls have also been observed on potted plants in nursery stock grown to feed laboratory colonies of the agent. Herein, our objective was to isolate and identify the causal agent of the galls and assess its ability to induce galls in naive plants. We obtained stem galls from both field and nursery plants, aseptically isolated a fungus in acidic potato-dextrose-agar, purified fungal colonies, and wound-inoculated stems of potted naive saplings with purified hyphal fragments, which induced galls like those observed in the field and nursery. Simultaneous molecular analysis of the fungal DNA from field and nursery plants, experimentally induced galls, and from fungal colony isolates identified this gall-inducing fungus as Cophinforma sp. We demonstrated that Cophinforma sp. can infect Brazilian peppertree stems via mechanical wounding and visibly discernable stem galls can develop in saplings within 3 months. This will serve as a model for galled plant production for assessing interactions between the thrips and this naturalized fungus, which may enhance S. terebinthifolia management efficacy.