Association of pectolytic fluorescent pseudomonads with postharvest rots of onion

Five isolates of pectolytic fluorescent pseudomonads were obtained from a rotted onion bulb and identified as Pseudomonas marginalis. At both 4 and 25 degrees C, all isolates caused soft rot to detached plant parts of onion and to carrot, celery, cucumber, pepper, spinach, tomato and turnip (but not garlic). They did not however cause any symptoms in living plants of these same species. These results suggest that the onion isolates are a postharvest pathogen which is not destructive in the field but becomes a threat to fresh vegetables stored at low-temperature. Analysis of cellulosolytic and pectic enzymes revealed that pectic lyases, but not polygalacturonases, pectin methyl esterases and cellulases were produced in culture by each isolate.