Early occurrence of Teratoramularia rumicicola in Japan: re-identification of historic strain GR1 and its pathogenic effects on Rumex species

Abstract

Teratoramularia rumicicola is a plant pathogenic fungus infecting Rumex species. Although it was described as a new species in 2016, its fundamental characteristics, including historical occurrence, geographic distribution, and host range, remain poorly resolved. In this study, we re-identified strain GR1, which was originally isolated from a diseased Rumex plant in the Bonin (Ogasawara) Islands in 1996 and deposited in a public bioresource center, together with the plant voucher specimen, and evaluated its host range. Colony and conidial morphology and a phylogenetic analysis based on concatenated internal transcribed spacer (ITS) and large subunit (LSU) rDNA sequences identified GR1 as T. rumicicola. Morphological examination of the host plant voucher specimen confirmed Rumex japonicus as the natural host. Pathogenicity assays demonstrated that GR1 infected R. japonicus, reproduced the original disease symptoms, and was successfully re-isolated from diseased tissues, consistent with Kochs postulates. In addition, GR1 caused significant disease and shoot biomass reduction in R. japonicus, R. crispus and R. obtusifolius. The identification of GR1 reveals the presence of T. rumicicola in Japan approximately two decades prior to its formal description, representing the earliest known record of this species. Furthermore, this finding extends its known distribution from temperate regions to the subtropical Bonin Islands, a well-preserved and isolated ecosystem. This study documents for the first time R. japonicus as a natural host of T. rumicicola.