English

Abstract

Abstract The crayfish plague disease agent, Aphanomyces astaci, has coevolved with the native European crayfish since its arrival to mainland Europe in the 1860s. There are indications that some of the A. astaci strains are of reduced virulence, while the resistance against A. astaci infection varies among native European crayfish stocks. In Lake Venesjärvi, Finland, a potential case of latent crayfish plague infection was observed in the early 2000s. We have isolated an oomycete from live Astacus astacus originating from Lake Venesjärvi and identified it as A. a staci of haplogroup A by specific qPCR, nuclear ITS and mitochondrial LSU and SSU sequencies, and named the isolate as UEF_VEN5/14. The A. astaci was isolated from a potentially latently infected A. astacus, subsequently identified, genotyped and proven to be of reduced virulence in a separate infection challenge experiment under laboratory conditions. These findings add to speculations of rather rapid coevolution of A. astaci and European native crayfish and support the reports on latent crayfish plague infections among wild native European crayfish.