Effectiveness of Bacteria and Yeasts from Apple Orchards as Biological Control Agents of Apple Scab

A total of 931 bacteria and yeasts were isolated from soil and different apple tissues collected in abandoned and commercial orchards. Ninety-two isolates that exhibitedin vitroantibiosis and 268 that did not (total 360) were tested for their ability to suppress scab (caused byVenturia inaequalis) on apple seedlings in the greenhouse. Thirty-two isolates completely inhibited germination of conidia ofV. inaequalis in vitroand 106 significantly reduced the amount of apple scab that formed on apple seedlings when they were applied 24 h before inoculation withV. inaequalis.No correlation existed betweenin vitroantibiosis and ability to suppress scab on seedlings; however, one isolate that was identified as an isolate ofPseudomonas syringae(isolate 508) prevented conidial germination and effectively suppressed scab to a level comparable to the fungicide captan. When compared to pathogenic isolates ofP. syringaethat were isolated from various crops, 508 suppressed scab to a greater extent except in one case.