Coccinonectria pachysandricola, causal agent of a new foliar blight disease of Sarcococca hookeriana

Authors: SALGADO-SALAZAR, CATALINA - US Department Of Agriculture (USDA); Shishkoff, Nina; LEBLANC, NICHOLAS - Oak Ridge Institute For Science And Education (ORISE); Ismaiel, Ed - Ed; COLLINS, MAXTON - North Carolina State University; CUBETA, MARC - North Carolina State University; Crouch, Jo Anne

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2018
Publication Date: 4/8/2019
Citation: Salgado-Salazar, C., Shishkoff, N., LeBlanc, N., Ismaiel, A.A., Collins, M., Cubeta, M.A., Crouch, J. 2018. Coccinonectria pachysandricola, causal agent of a new foliar blight disease of Sarcococca hookeriana. Plant Disease. 103(6):1337-1346. https://doi.org/10.1094/PDIS-09-18-1676-RE.
DOI: https://doi.org/10.1094/PDIS-09-18-1676-RE

Interpretive Summary: Plants such as boxwood, pachysandra and sweet box are high-value broadleaf evergreen shrubs and groundcovers widely planted in landscapes worldwide. In September 2016, a new and unusual blight disease was found on several sweet box plants at the U.S. National Arboretum in Washington D.C. The diseased sweet box were growing next to a stand of severely blighted pachysandra. The goal of this study was to identify what was causing this new sweet box disease and to determine whether it could also infect pachysandra and boxwood. Even though they came from different plants, fungi isolated from the diseased pachysandra and sweet box plants were identical based on their appearance and their DNA fingerprints, and were identified as a fungus named Coccinonectria pachysandricola. This fungus has been known to cause volutella blight disease of pachysandra since the 1940s, but has never been described from other plants. Infectivity trials showed that the fungus isolated from both plants could cause disease in pachysandra and sweet box, but did not affect boxwood. In contrast, a different volutella blight fungus collected from boxwood did not cause disease in pachysandra or sweet box plants. Wounded plants had higher levels of disease than unwounded plants. However, wounding was not required, and even unwounded plants became diseased when infected by these fungi. Knowledge of this new disease and the conditions that allow the disease to occur will be useful to growers, horticulturalists, plant pathologists, disease diagnostic clinics, and regulatory agencies working to control diseases of these important landscape plants.

Technical Abstract: Woody plants in the Buxaceae family, including species of Buxus, Pachysandra and Sarcococca, are widely grown ornamental evergreen shrubs and groundcovers. Severe leaf spot symptoms were observed on Sarcococca hookeriana at the U.S. National Arboretum in Washington D.C. in 2016. Affected plants were growing adjacent to Pachysandra terminalis exhibiting volutella blight symptoms. Fungi isolated from both hosts were identical based on morphology and multilocus phylogenetic analysis and identified as Coccinonectria pachysandricola (Nectriaceae, Hypocreales), causal agent of volutella blight of Pachysandra spp. Pathogenicity tests established that C. pachysandricola (Cp) isolated from both hosts caused disease symptoms on P. terminalis and S. hookeriana, but not on Buxus sempervirens. Artificial inoculations with Pseudonectria foliicola (Pf), causal agent of volutella blight of B. sempervirens, did not result in disease on P. terminalis or S. hookeriana. Wounding enhanced infection by Cp and Pf, but was not required for disease development. Whole genome datasets were generated as resources for the fungi causing Buxaceae volutella diseases: C. pachysandricola, P. buxi and P. foliicola, ranging in size from 25.7 to 28.5 Mb. To our knowledge, this foliar blight of S. hookeriana represents a new disease for this host, and is capable of causing considerable damage to infected plants.