Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2021
Publication Date: 2/9/2022
Citation: Jones, R.W., Perez, F.G. 2022. First report of southern blight, caused by athelia rolfsii (syn. sclerotium rolfsii) on hellebores in north america. Plant Disease. https://doi.org/10.1094/PDIS-09-21-2004-PDN.
Interpretive Summary: Plant diseases continually damage ornamentals in the cultivated landscape, and plants with few diseases are most desirable. A popular perennial landscape plant with minimal disease problems is lenten rose. A new disease has been identified which is the most damaging of the few diseases found on lenten rose. Total collapse of the plant can occur due to attack of the stems near the soil line. As a newly reported pathogen of lenten rose, landscapers and home gardeners will need to consider this disease problem when planting lenten rose.
Technical Abstract: Lenten rose (Hellebores hybridus) is an herbaceous perennial grown in landscapes and valued for early spring flowers and high levels of deer resistance. An additional benefit as a landscape plant comes from the high level of disease resistance, with only three fungal pathogens reported in North America. In August of 2021, a Lenten rose plant within a mature landscape in Silver Spring, MD, USA, was found with a collapsed canopy and brown stems near the soil line. Small clusters of brown sclerotia-like objects were seen along the stem. Samples of the sclerotia and diseased tissue were dipped in 70 percent ethanol for 15 sec, transferred to 5 percent NaClO for 30 sec, immersed in sterile water for one minute, then plated onto Potato Dextrose Agar. Sclerotia-like objects germinated and white mycelia covered the plates within five days of germination. Hyphae emerged from diseased tissue within two days and also grew rapidly. Cultures from sclerotia-like objects and diseased tissue produced white sclerotia which melanized to brown spherical sclerotia ranging in size from two to four mm. Culture samples (1 cm square) were excised from the culture plates and transferred to the base of three two-year old potted hellebore plants. Control plants had blocks of PDA placed at the base of the plants. Plants were placed in plastic bags for two days to maintain humidity, then maintained at room temperature without plastic bags. Petioles turned brown and leaves collapsed within seven days of inoculation. White, fan-like hyphae were present along with maturing sclerotia. Samples from surface sterilized tissue and sclerotia produced the same culture morphology as the originally isolated cultures. Non-inoculated plants remained healthy. Individual DNA samples were prepared from original cultures and the re-isolated cultures. Molecular identification was performed by amplification of the internal rRNA transcribed spacer region (ITS1/4), the large subunit rRNA (LSU), and the elongation factor-1A (EF1a). Amplification products were cloned into TOPO-TA pcr4 vector and sequenced. Homology to ITS1/4 was found with Athelia rolfsii (MN622806), to LSU with Athelia rolfsii (MT225781) and for EF1a with Athelia rolfsii (MW322687). This is the first report of Sclerotium rolfsii on Hellebores in North America (Farr, D.F & Rossman, A.Y. Fungal Databases, U.S. National Fungus Collections, ARS, USDA. Retrieved September 10, 2021). This report is unique in that few fungi are known to infect Hellebores and southern blight is not commonly isolated in landscape plantings at Maryland latitudes.