Abstract: A yeast strain was tested for its antagonistic activity against blue mold (Penicillium italicum) and green mold (Penicillium digitatum) of citrus fruit in bean sprout juice agar (BSJDA) medium. The strain (34-9) was identified as Kloeckera apiculata and showed the highest antagonistic activity against citrus blue mold and green mold on pair-culture against P. italicum and P. digitatum of citrus and on wounded citrus fruit. There was no antagonistic activity of fermentated filtrate and after sterilization. Observation by scanning electron microscopy revealed attachment of the yeast cells to the pathogen hyphae, indicating that the high antagonistic activity of the yeast may be contributed by the competition for space and nutrients and /or involvement of direct antagonist of the yeast on the fungus.

Key words: Penicillium italicum, Penicillium digitatum, Antagonistic microorganism, Kloechera apiculata