A novel medium for the oosporogenesis of Aphanomyces cochlioides

Reliable production of infective spores is an essential requirement in the screening of putative biological control agents. We report the development of a novel and simple medium for the production of viable oospores of Aphanomyces cochlioides, one of the principal causes of damping-off of sugar beet. The semi-solid medium consists of 5 g l(-1) corn meal agar and 1 g l(-1) mycological peptone and supports the development of 2.25 x 10(5) oospores cm(-2) in 5 d. In a plant bioassay for post-emergence damping-off, the oospores had a consistent pathogenic effect with 50+/-5.7% damping-off induced by 170 oospores g(-1) soil (-15 kPa matric potential) after 20 d. Higher numbers (1700 g(-1) soil) produced 88.8+/-9.1% disease in emerged plants after 20 d.