Reemergence of Cylindrocladium Crown Rot of Roses in Florida

Abstract

On April 2017, four out of 10,000 Double Knock Out Red roses were observed presenting partially wilted and chlorotic foliage in a commercial nursery in Gadsden Co., Florida. Closer examination of the plant crown revealed brown discoloration of the woody tissue. Under high temperature (85°F) and humidity (70%), shoots progressively turned chlorotic and necrotic, leading to plant death in 4 months. A rapid-growing fungus presenting orange-brown mycelium and abundant cylindrical spores was isolated from infected woody crown tissue. BLAST analysis of the resulting sequence (GenBank no. MT019606) of this pathogen had 100% identity to Calonectria cylindrospora β-tubulin gene (GenBank no. FJ918509.1). Koch’s postulates were conducted on healthy Double Knock Out roses. Two weeks after inoculation, shoots of inoculated plants turned progressively chlorotic and then necrotic, leading to plant death in 2 months. The same pathogen was reisolated from infected plant parts, which sequence also had 100% identity to C. cylindrospora β-tubulin gene (GenBank no. FJ918509.1). This pathogen is the same as one of three isolated from crown rot of roses back in 1994 and identified as Cylindrocladium scoparium (teleomorph: C. cylindrospora [Ellis & Everh.]). In this new occurrence, all infected plants were removed from the nursery, and no further infections were detected. This finding is important for commercial growers to be aware of the potential presence of this pathogen in their nurseries. Knowing the symptoms will help them recognize the disease and take action to prevent spread of the disease.