Pseudomonas fluorescens and low doses of chemicals inhibit postharvest decay of apples in commercial storage

Postharvest diseases pose serious threats to the pome fruit industry worldwide. Grey mould, Mucor rot and blue mould decay on apples, caused by Botrytis cinerea, Mucor piriformis and Penicillium expansum, respectively, are the most economically important postharvest fungal pathogens in apple storage in British Columbia, Canada. The biocontrol capability of Pseudomonas fluorescens isolate 4-6 alone, or in combination with calcium chloride (CaCl2), sodium bicarbonate (SBC) or salicylic acid (SA), against B. cinerea, M. piriformis and P. expansum was evaluated in vitro and on 'Ambrosia' apple in commercial cold storage at 1 degrees C. The combination of the antagonist with the chemical additives generally did not enhance the level of control of the pathogens in vitro. The combination of isolate 4-6 with SBC did provide levels of control of B. cinerea, M. piriformis and P. expansum comparable to the commercial fungicide Scholar (R) on 'Ambrosia' apples after 15 weeks in cold storage. The biocontrol capability of P. fluorescens isolates 1-112, 2-28 and 4-6 to control B. cinerea, M. piriformis and P. expansum was also evaluated on 'Ambrosia' apples in commercial controlled atmosphere (1.5% CO2 + 1.2% O-2) storage at 1 degrees C. All three isolates of P. fluorescens significantly (P < 0.05) inhibited the development of grey mould and blue mould on 'Ambrosia' apples after CA storage, and provided levels of control comparable to BioSave (R) (containing Pseudomonas syringae ESC-10). These results suggest that P. fluorescens has the potential to control common postharvest fungal pathogens during commercial storage, and by combining the antagonist with SBC, decay can be reduced to a commercially acceptable level.