Aphanomyces sinensis sp. nov., isolated from juvenile soft-shelled turtle, Pelodiscus sinensis, in Japan

A species of Aphanomyces was isolated from juvenile soft-shelled turtles, Pelodiscus sinensis, cultured in Japan. Typically, an infected turtle showed small whitish maculae on the carapace. Many hyphae were observed in the epidermis. The hyphae were isolated using glucose–yeast (GY) agar plates. The morphological characteristics were very similar to those of Aphanomyces laevis, but a clear nuclear spot was observed in the center of the oospore in the strains isolated from the soft-shelled turtles. The optimal growth temperature for the isolates was 25–30°C and the optimum pH was 6–9. Experimental infection tests with isolates produced small whitish maculae on the carapace, and soft-shelled turtles artificially infected with the zoospores showed high mortality, especially in the high-dose group. Phylogenetic analysis based on the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) indicated that the isolates from the soft-shelled turtles were unidentified species of Aphanomyces. As a result, the strain was described as a new species, Aphanomyces sinensis.