A Diagnostic Guide for Volutella Blight Affecting Buxaceae

Abstract

Volutella blight is a common disease of species in the plant family Buxaceae, specifically boxwood, pachysandra, and sarcococca. Even though the disease has been consistently found over the past 150 years in all continents except for Antarctica, there are numerous complications in its etiology, signs and symptoms, and taxonomy, morphology, isolation, and preservation methods of its causal pathogens. For example, one of the two pathogens causing Volutella blight on boxwood, Pseudonectria buxi, has gone by at least 25 names including Volutella buxi and P. rousseliana, since its original description in 1815. The other Volutella blight pathogen on boxwood, P. foliicola, was not described until 2015. Although Coccinonectria pachysandricola, previously named as V. pachysandricola, has been known as a pathogen of pachysandra since 1944, it is only recently found in 2019 that the same pathogen can infect sarcococca. In this diagnostic guide, we provide a comprehensive review on the taxonomy, symptoms, host range, distribution, isolation, identification, storage, and pathogenicity test of the Volutella blight disease and these three causal pathogens. New data, such as previously unreported perithecial morphological characters of P. buxi and a unique sporodochia-forming pattern of C. pachysandricola, are also provided in this guide. Furthermore, a detailed comparison of diagnostic traits of three major fungal diseases on boxwood, namely, Volutella blight, boxwood blight, and boxwood dieback, is included. This guide aims at providing integrated information to aid the diagnosis of Volutella blight and facilitating new research to advance our knowledge of this old but under-studied disease.