Homothallic sexual reproduction of Pustula helianthicola and germination of oospores

► 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 Pustula resembles the modes known from Albugo candida.