First single zoospore infection with an Albuginaceae provides genetically homogenous strains. ► Homothallism of P. helianthicola was shown by oospore formation in unithallic infections.
► Developmental details of gametangia and oospore formation were shown microscopically.
► Infection of sunflower was achieved with oospores of P. helianthicola for the first time.
► Oospore germination of Pustularesembles the modes known from Albugo candida.