Studies on the Effect of Postharvest Treatment of a Biological Control Agent, Pseudomonas Syringae, on Post Harvest Blue Mold and Gray Mold of Apple

Blue mold of apple (caused by Penicillium sp.) was identified as one of the reemerging postharvest diseases of apple in Ontario. In 2004, a project, funded by the AAFC IFSP, Minor Use Program, was initiated to test the efficacy of biological control agents on blue and gray mold development on stored apples. Three concentrations of BioSave were tested on ‘Empire’ and ‘McIntosh’ at Vineland, and on ‘Gala’ and ‘McIntosh’ at Summerland. At Vineland, the evaluation of disease incidence after 168 days in cold storage showed that both apple cultivars, ‘Empire’ and ‘McIntosh’, treated with the three concentrations of BioSave alone or in combination DPA resulted in significantly lower disease incidence of blue mold than control.

Treating apples with 2.38 g/L of BioSave provided the highest blue mold disease reduction. There is some indication that mixing BioSave with DPA may have a detrimental effect on BioSave efficacy on blue mold. This will be tested further in the 2006-07 season. There was a significant reduction of gray mold with BioSave in both ‘McIntosh’ and ‘Empire’ apples.

Water treated apples had a high percentage of gray mold incidence, and this could be due to the nature of B. cinerea, a nesting pathogen, in that the pathogen was spread over the neighbouring fruit in the crates and masked the effect of BioSave treatment. Placing of apples after cold storage resulted in an increase of blue and gray mold incidence. At Summerland, the application of BioSave reduced blue mold and gray mold diseases in ‘McIntosh’ and ‘Gala’ apples. In summary, during the 2-year study (2004-05, 2005-06), the postharvest treatment of Pseudomonas syringae in combination with DPA gave effective control of blue mold and gray mold on ‘McIntosh’ and ‘Empire’ apples for up to 168 days in CA and cold storage.