First Report of Pythium myriotylum on Lemna gibba in Israel

Much interest has focused on duckweed as an alternative food source. Commercial production of Lemna gibba was initiated in Israel in 1991. During the summers of 1994 and 1995, Lemna gibba was grown commercially in covered ponds. In these two seasons, the plants were found to be infected by Pythium myriotylum, which has previously been reported as a pathogen of duckweed (1). In the ponds where the plants were held at high density, small, wilted, white patches of plants were recognized in early June. By the end of the month over 70% of the plants were infected and died. Microscopic examination of infected plants showed the presence of fungal appressoria and mycelial growth. Fungi were isolated from the plants onto potato dextrose agar (PDA). Ten isolates grown on PDA for 7 days were used to inoculate healthy plants. After 12 days, symptoms developed on plants at 28 or 32°C. Symptoms were similar to those observed on pond-grown plants. Plants maintained at 17 or 22°C did not become infected. The results from the pond and laboratory work showed that high plant density and temperature above 24°C were necessary for infection, and infection takes place by hyphal elements that spread in the water. This is the first report of Pythium myriotylum on Lemna gibba in Israel. Reference: (1) E. Rejmankova et al. Veröff. Geobot. Inst. Eidg. Tech. Hochsch. Stift. Rübel, Zür. 87:178, 1986.