PHYSIOLOGICAL-STUDIES ON HALOPHYTOPHTHORA-VESICULA (STRAMINIPILOUS FUNGI) ISOLATED FROM FALLEN MANGROVE LEAVES FROM MAI-PO HONG-KONG

Fallen leaves of Kandelia candel and Acanthus ilicifolius from the Mai Po Nature Reserve, Hong Kong, were collected and returned to the labo ratory for the isolation of marine species of Halophytophthora (Strami nipilous fungi). Discs of leaf samples were washed with sterile artifi cial seawater (ASW) and inoculated into peptone-yeast-extract-glucose- seawater (PYGS) broth supplemented with antibiotics to inhibit bacteri al growth. Three isolates (LEM-022 and LEM-036 from Kandelia candel an d LEM-031 from Acanthus ilicifolius) were selected, characterized and identified as Halophytophthora vesicula. Discs from a 7 day-old cultur e on V8-juice agar were transferred into sterile ASW for the character ization of zoosporangia and observation of zoospore release. Productio n of zoosporangia and release of zoospores were observed 18-24 hours a fter transfer. Zoosporangia of the three isolates varied in morphology , while the zoospores were biflagellate, and ovoid to reniform in shap e. The optimum pH for growth was pH 7 to 8 and optimum temperature was from 25 to 30 degrees C. All isolates grew from zero to 60 parts per thousand salinity with strong growth at 15-25 parts per thousand. The optimum pH for sporulation was pH 7 for all isolates at the following temperature and salinity levels: 25-30 degrees C and 5-30 parts per th ousand for isolate LEM-022; 15-30 degrees C and 10-15 parts per thousa nd for LEM-031; and, 15-30 degrees C and 5-20 parts per thousand for L EM-036.