THE INFLUENCE OF MOISTURE ON THE SUPPRESSION OF PSEUDOMONAS-SYRINGAE BY AUREOBASIDIUM-PULLULANS ON AN ARTIFICIAL LEAF SURFACE

Isolates of Aureobasidium pullulans which produce antibacterial metabo lites were compared with non-antibiotic-producing isolates of Tremella foliacea and Trichosporon beigelii for their ability to inhibit growt h of Pseudomonas syringae pv phaseolicola. The bacteria and fungi were co-inoculated on an artificial leaf surface under conditions of low a nd high water availability. Under conditions of excess moisture, antib iotic production gave no advantage to the Aureobasidium isolates, and all the yeasts were equally antagonistic. Under drier conditions the A ureobasidium isolates reduced the population of P. syringae by 96-99%, a result which was significantly different from that which occurred w hen the bacteria were co-inoculated with the other yeasts under these conditions. An antibacterial compound, similar to that produced in liq uid culture by Aureobasidium, was detected in washings from the artifi cial leaf surface following growth of this species.