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 de velopment of a novel and simple medium for the production of viable oo spores of Aphanomyces cochlioides, one of the principal causes of damp ing-off of sugar beet. The semi-solid medium consists of 5 g l(-1) cor n meal agar and 1 g l(-1) mycological peptone and supports the develop ment of 2.25 x 10(5) oospores cm(-2) in 5 d. In a plant bioassay for p ost-emergence damping-off, the oospores had a consistent pathogenic ef fect with 50+/-5.7% damping-off induced by 170 oospores g(-1) soil (-1 5 kPa matric potential) after 20 d. Higher numbers (1700 g(-1) soil) p roduced 88.8+/-9.1% disease in emerged plants after 20 d.