A new species of Cercospora on Helmholtzia glaberrima

Abstract

A Cercospora (ICMP 17857) was isolated from Helmholtzia glaberrima and morphologically identified as Cercospora apii. C. apii had never been isolated from H. glabberima casting doubt on its classification. DNA extraction was conducted followed by multi-gene sequencing of ICMP 17857 and other Cercospora isolates from Landcare Research’s ICMP collection. Phylogenetic trees generated from this data revealed ICMP 17857 and four other ICMP isolates belonged within a monophyletic group that had yet to be described as a species. This group has been referred to as Cercospora species I in a previous publication and had been isolated from a variety of plant host species. A consolidated species approach was undertaken to generate enough data to formally describe this group as a species. Morphological data including colony morphology, colony size at cardinal temperatures and asexual reproductive structure descriptions were collected. Ecological data comprising of pathogenicity testing to ascertain Cercospora species I host was conducted. Morphological data revealed unique colony diameters at different cardinal temperatures with little variation between isolates and small differences in morphological structures. The true host of Cercospora species I could not be determined as no interactions were observed between Cercospora species I and the plant species tested. It was found that Cercospora species I could grow saprobically on a variety of autoclaved host tissue offering an explanation to the wide variety of plant species it had been isolated from. It was concluded that Cercospora species I should be described as a new species based on the combined genetic and morphological data collected.