First report of Agroathelia rolfsii causing Southern blight on eggplant in New York

Eggplant (Solanum spp.) is a widely grown fresh market crop in New York, with a total of 262 acres grown on 564 farms in 2022 (USDA-NASS 2024). In July 2024, one eggplant (Solanum melongena cv. Snowy) was found wilted in a research field trial at the Hudson Valley Research Laboratory in Highland, NY. The field site was previously planted with apple trees, which were removed in 2023. The diseased eggplant had a necrotic lesion at the crown covered with white mycelial mats spreading over the stem. Diseased tissue was surface sterilized with 5% bleach for 60 s, plated on potato dextrose agar (PDA) and incubated at 25 °C under natural lighting. Morphological characteristics of the resulting fungal growth resembled those of Agroathelia rolfsii. Cottony mycelia grew rapidly in a radial pattern and was white to off-white in color. Spherical, ellipsoid, and irregular-shaped sclerotia formed near Petri plate edges, initially whitish, then turning tan and eventually dark red-brown, often reaching 2-5 mm in diameter. The isolate (EP24-1) was grown in potato dextrose broth for 1 week before harvesting mycelial tissue through vacuum filtration. Genomic DNA was extracted using a DNeasy Plant Mini Kit (Qiagen) following the manufacturer’s instructions. PCR assays using species-specific primers SCR-F/SCR-R (Jeeva et al. 2010) and primers EF595F/EF1160R (Mascarenhas and Quesada-Ocampo 2024) were used to amplify products in the internal transcribed spacer (ITS) and the translation elongation factor 1 alpha (EF-1α) regions. Products were Sanger sequenced and deposited in GenBank. The ITS sequence (PV606914) shared 100% (544/544 bp) identity with Agroathelia (Athelia) rolfsii accession MH858139.1, and the EF-1α sequence (PV833089) shared 97% (521/539 bp) identity with A. rolfsii accession MN262527.1. To fulfill Koch’s postulates, healthy 6-week old eggplants (cvs. Snowy, Black Beauty, and Nadia) were inoculated in a greenhouse. There were 6 replicates per variety for each of the 3 treatments. EP24-1 was grown on PDA and 7 mm plugs were placed mycelia-side down against the base of the plant stems. Sterile PDA plugs were used for mock-inoculations and plants were left uninoculated as controls. Plants were covered with a plastic bag overnight. The following day, plants were moved to a growth chamber at 19°C with a 12-h photoperiod, misted to maintain >80% relative humidity. Symptoms of infection were visible 4-5 days post inoculation (dpi) and included water-soaked lesions, mycelial growth, and sclerotia formation. At 14 dpi, 2 of the 6 inoculated Snowy plants, 5 of the 6 inoculated Black Beauty plants, and 1 of the 6 inoculated Nadia plants had developed symptoms, while mock and uninoculated control plants remained asymptomatic. Symptomatic stem tissue at lesion margins was surface sterilized for 60 s in 10% bleach and plated onto 25% acidified PDA. The isolated fungus was identified as A. rolfsii through morphological and molecular characterization. To our knowledge, this is the first report of A. rolfsii infecting eggplant in NY State. This pathogen causes Southern blight disease in tropical and subtropical regions and is capable of infecting over 500 plant species (Xie et al. 2014). A. rolfsii has previously been reported in NY on other hosts including table beet (Pethybridge et al. 2019) and pale swallow-wort (Gibson et al. 2012). The detection of A. rolfsii on eggplant in NY signals the need for continued monitoring of this pathogen in higher latitudes.