Epipremnum pinnatum (L.) Engl., (Araceae, Monocots) known as dragon-tail plant or centipede tongavine, is the most cultivated aroid species worldwide (Boyce 2004). In 2022, symptomatic dragon-tail plants, collected from plant nurseries in south Florida (e-Xtra Fig.1). Symptoms included round leaf spots often with a yellow halo and erupting pustules mainly distributed in the underside of the leaves. Visits to the nurseries revealed a 60% incidence of approximability 50 mature plants, with some leaves showing up to 30% of tissue damage. The putative pathogen was identified morphologically as Pseudocerradoa paullula (Syd. & P. Syd.) M. Ebinghaus & Dianese (Pucciniaceae, Basidiomycota) (Ebinghaus et al. 2022), characterized by the production of pseudosuprastomatal uredinia with globose to subglobose urediniospores, light-brown, echinulate (1 µm height), 24-31 µm diam with thick walls, 1.5-2.5 µm in height (n=30). Identical morphological features reported by Urbina et al. (2023) (e-Xtra Fig. 1). PCR amplification followed by Sanger sequencing of the internal transcribed spacer (ITS) and large subunit (LSU) of the ribosomal RNA genes (Aime 2006) together with LSU internal species specific primer (Urbina et al. 2023) were used to confirm the identification of the pathogen (GenBank ON887194-ON887196). MegaBlast (Chen et al. 2015) searches resulted in a >99% sequence similarity to a P. paullula specimen collected in Florida (2019-101665, GenBank ON887197). Host identification was made by using the Ribulose-1,5-bisphosphate carboxylase-oxygenase (rbcL. GenBank ON887186, ON887187) and Maturase K (matK) loci (GenBank ON887190, ON887191) (Fazekas et al. 2012). Both barcodes resulted in >99.13% sequence similarity to voucher J.R. Abbott 24912 FLAS (GenBank GU135198 and GU135036, respectively). Symptomatic dried specimens were deposited in the Plant Industry Herbarium (PIHG 16229 - 16232). Koch's postulates were fulfilled using urediniospores collected from an infected E. pinnatum sample that was kept in darkness at 4°C for seven days until inoculation. Eight potted dragon-tail plants were inoculated by hand rubbing urediniospores against upper and lower leaf surfaces and three plants were used as controls. All plants were misted with sterile water and covered with plastic bags (23 °C, >90% RH, 12/12 h daylight). Bags were removed 48 h after inoculation, plants were set in a climate-controlled greenhouse (~30 °C, ~65% RH, 12/12 h light cycle) and monitored daily for symptoms. Chlorotic spots appeared after 10 days, and pustules after 25 days while the non-inoculated controls remained symptomless. Aroid leaf rust is known to infect several aroid species, including dragon-tail (Shaw 1995), which some varieties capable to outdoors in USDA 9a hardiness zones (Wunderlin et al. 2023), but the rust fungus has not been observed on any species of Epipremnum in the landscape yet, suggesting that its susceptibility could be driven by plant growth conditions that favor pathogen infection (e.g., excess of humidity and nutrients, dense planting, overhead irrigation, etc.). Here we encourage dragon-tail plant growers to be aware of its susceptibility to P. paullula and to stay vigilant of the culture conditions to avoid plants from getting infected with this airborne pathogen.
Keywords: Causal Agent; Crop Type; Disease management; Fungi; Ornamentals; Subject Areas.