First report of Parvodontia relampaga causing relampago blight on the critically endangered Florida Torreya ( Torreya taxifolia ) and its occurrence on nine

Parvodontia relampaga is a recently described phytopathogenic fungus from Florida, USA that causes relampago blight (RB), a disease characterized by the formation of white rhizomorphs on branches and mycelial fans on leaves followed by leaf necrosis and senescence (Paez et al. 2024). P. relampaga can be distinguished from other thread-blight fungi because it produces gloeocystidia (yellow, obclavate to irregular thick-walled cells). To date P. relampaga has been documented on 27 host species. Since the description of P. relampaga, there have been several observations of white rhizomorphs and blight symptoms on the endangered conifer species, Torreya taxifolia, on private property near Torreya State Park in Liberty County, Florida. At the time of these reports, we were unable to access the property and collect diseased plants. To confirm that P. relampaga can cause RB on T. taxifolia, we inoculated eight T. taxifolia plants with 15 mm mycelial plugs of a P. relampaga paratype (NRRL 64415). Two T. taxifolia plants were inoculated with sterile plugs as controls. The plants were kept in a 22° C greenhouse with a 40% shade cloth and were watered with sprinklers for 10 minutes every 12 hours. The experiment was conducted twice. After 60 days, we observed leaf senescence and white rhizomorphs on stems, branches, and leaves of seven plants out of 16 inoculated plants. No symptoms or rhizomorphs appeared on the negative controls. We isolated rhizomorphs on potato dextrose agar (PDA) and confirmed their identity by sequencing the ribosomal internal transcribed spacer (ITS) region using primers ITS1F-ITS4 (Gardes and Bruns 1993). The sequence (PX765047) was 99% similar to NRRL 64415 based on BLAST analysis. In September 2025, we obtained access to the private property and collected T. taxifolia needles with white rhizomorphs and leaf necrosis. We cultured the fungus on PDA and confirmed the identity by sequencing ITS, the ribosomal large subunit (LSU) with LR0R-LR5F (Hopple and Vilgalys 1994; Tedersoo et al. 2008), and the translation elongation factor-1 alpha (tef1) with EF1-983F-EF1-1567R (Rehner and Buckley 2005). The isolate showed ≥ 99% similarity to P. relampaga at each locus (PX629132, PX625962, PX659862). We also observed RB symptoms and signs on eight additional hosts across Florida: Camphora officinarum, Cartrema americanum, Citrus reticulata, Damburneya coriacea, Gordonia lasianthus, Illicium floridanum, Ligustrum lucidum, and Sabal palmetto. We confirmed the identity of the fungi on all hosts with DNA sequencing (PX625961, PX629131, PX625963–PX625970, PX629133, PX629135–PX629140, PX659859– PX659861, PX659863, PX659864); all sequences showed ≥ 99% similarity to P. relampaga. We were unable to sequence tef1 for some collections but the fungal morphology and both ITS and LSU sequences were consistent with P. relampaga. Due to time constraints and limited access to host plants, we only fulfilled Koch’s Postulates for Torreya taxifolia. Nonetheless, it is important to note that RB occurs on a wide array of plant species. Although it is unlikely that RB is primarily responsible for the death of individual T. taxifolia trees (which is often due to cankers caused by Fusarium torreyae (Smith et al. 2011)), P. relampaga is likely contributing to the ongoing decline of T. taxifolia. Our work, in combination with the original report by Paez et al. (2024) brings the total number of known RB hosts to 36 species across 24 families.