Root Rot and Stunting of Hydroponically Grown Endive, Fennel, and Sorrel Caused by Pythium F-group in South Africa

Specialized vegetable crops such as endive (Cichorium endiva), fennel (Foeniculum vulgare), and sorrel (Rumex spp.) are being cultivated hydroponically in South Africa to be marketed as admixtures in salads. Stunted growth accompanied by browning and rotting of the root tips has been observed at a commercial recirculating gravel bed hydroponic system near Pretoria during the warm summer months. Root segments excised from symptomatic plants were rinsed in sterile water and plated on Pythium selective medium (1). Pythium F-group, characterized by the production of noninflated filamentous sporangia and no oospores (2), was isolated from 40% of endive, 60% of fennel, and 7% of sorrel root segments. Koch's postulates were confirmed by inoculating 4-week-old seedlings of each crop in the greenhouse with a Pythium F-group isolate from the particular crop. Inoculations were performed by adding 3 ml of suspension (10 5 zoospores per ml) to each liter of aerated nutrient solution. Control plants received no inoculum, and the experiment was repeated once. After 4 weeks, inoculated plants showed stunting of the foliage and slight to moderate root rot. Pythium F-group could readily be reisolated from roots of inoculated plants. To our knowledge, this is the first report of Pythium F-group on these crops in South Africa. References: (1) W. J. Botha and R. L. J. Coetzer. S. Afr. J. Bot. 62:196, 1996. (2) M. W. Dick. Keys to Pythium. University of Reading Press, Reading, UK, 1990.