Occurrence of Aphanomyces cochlioides Damping-off of Sugar Beet in Spain. M. C. Ramirez, Unidad de Patologia Vegetal, E.T.S.I. Agronomos, Ciudad Universitaria. R. Raposo, Departamento de Proteccion Vegetal, CIT-INIA, Carretera de la Coruna 7, 28040 Madrid, Spain; and E. Mateo-Sagasta, Unidad de Patologia Vegetal, E.T.S.I. Agronomos, Ciudad Universitaria. Plant Dis. 78:102. Accepted for publication 28 July 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0102D.
Abnormally cold weather in the spring of 1991 caused late sowing or resowing of sugar beet (Beta vulgaris L.) in May and early June in northwestern Spain. Several commercial fields developed postemergence damping-off. Symptoms consisted of a brown discoloration of the hypocotyl that began at the soil surface and frequently extended to the base of the cotyledons. Infected seedlings were incubated in sterile water at 25 C. After 24 hr, sporangia developed and grapelike clusters of encysted spores formed at the tip. Symptoms and morphological description of the pathogen conformed to those of the seedling disease caused by Aphanomyces cochlioides Drechs. Seven-day-old sugar beet seedlings grown from surface-treated seed of cv. Oryx were grown in pots in a greenhouse and inoculated by adding a solution of zoospores or oospores (30,000-50,000/ml) to the pot. After 5 days, seedlings developed symptoms observed in the field, and A. cochlioides was reisolated from all diseased seedlings. The pathogen was not isolated from plants in commercial fields that had been sown by March (usual sowing time) and had developed seedling diseases. Occurrence of A. cochlioides on diseased seedlings was associated with late-sown beets. This is the first report of A. cochlioides on sugar beet in Spain