Rodrigo A. Valverde and Sead Sabanadzovic
Japanese holly fern (Cyrtomium falcatum) is a popular fern in the southeastern United States. This plant is native to Japan. It forms a rounded mound that can be up to 3 feet wide and 1 1/2 feet tall. The foliage is glossy and very dark green. The individual leaflets are leathery and serrated with sharp points resembling holly leaves, thus the common name. Japanese holly fern is evergreen in frost-free areas but loses its fronds in colder climates. It is normally grown outside in part shade as filler with impatiens, caladiums or other ferns as a contrast in color and texture. This fern makes an attractive border around large trees or shrub beds. Until now, this plant was considered to have little disease or pest problems.
During the past five years, a viral-like disease on Japanese holly fern has increased in occurrence in Louisiana and Mississippi. Plants showing symptoms of yellow-mottled leaves have been observed in home gardens, public landscapes and local nurseries in Louisiana and Mississippi. Diseased plants also exhibited reduced growth and premature leaf death. Homeowners in Louisiana and Mississippi have noticed the symptoms and pointed out the problem to plant disease clinics. On the LSU campus in Baton Rouge where Japanese holly fern is common landscape plant, approximately 90 percent of the plants show the virus symptoms (Figure 1).
Since early 2006, researchers from the LSU AgCenter and Mississippi State University have been conducting a collaborative research project on this problem. The main objective is to identify and characterize the causal agent, as well as to study ways the disease is dispersed.
Analyses of double-stranded RNA (dsRNA) extracted from infected Japanese holly fern plants revealed several dsRNAs. These dsRNAs were not present in healthy plants, supporting the belief a virus is the likely cause of the disease. The dsRNAs from infected plants were used to construct a cDNA library, and preliminary information indicates that the fern virus belongs to a new viral species. A procedure was developed to detect the virus, and it was found in foliar tissues (both showing symptoms and with no obvious symptoms) of infected Japanese holly ferns
Attempts to transmit the virus by mechanical inoculations to several plant species – including ferns – failed. Graft transmission experiments therefore were conducted by grafting tissue from infected plants onto healthy plants. Symptoms developed in the grafted plants three to five weeks after grafting.
The disease caused by this virus appears to be distributed throughout the South. Japanese holly ferns showing viral symptoms have been observed in public landscapes in Alabama, Arkansas, Texas and Tennessee. Testing these plants confirmed the presence of the same virus isolated in Louisiana and Mississippi. Researchers have observed an increase in the number of infected plants in various locations, suggesting a natural vector exists for the virus.
Homeowners and landscape professionals are advised to purchase plants that don’t exhibit foliar yellowing symptoms and to destroy diseased plants, particularly when they are next to healthy plants.
Further research is being conducted to learn more about the biology of this virus and to determine the means of natural spread of this emerging viral disease.
Rodrigo A. Valverde, Professor, Department of Plant Pathology and Crop Physiology, LSU AgCenter, Baton Rouge, La.; and Sead Sabanadzovic, Associate Professor, Department of Entomology and Plant Pathology, Mississippi State University, Starkville, Miss.
(This article was published in the spring 2008 issue of Louisiana Agriculture.)