Biocontrol of apple postharvest decay by Aureobasidium pullulans

The activity of two biological control agents, strains L1 and L8, previously identified as Aureobasidium pullulans, was tested on apple, artificially inoculated with Botrytis cinerea (grey mould), Colletotrichum acutatum (bitter rot) or Penicillium expansum (blue mould). The washed cells of antagonists controlled over 86% of three types of decay. The cell concentration of both antagonists was highly correlated with their efficacy, the R2 ranging from 0.93 to 0.99. The highest concentration (108 CFU mL−1) of L1 and L8 provided the best control of B. cinerea, C. acutatum and P. expansum, although grey mould was completely inhibited also by a concentration one log lower (107 CFU mL−1). The population dynamics of L1 strain in ‘Gala’ apple increased almost 8-fold during the first 48 h after treatment and remained elevated until 7 d, revealing that, although the antagonist was isolated from the carposhere of peach fruit, it showed good adaptation in other wound environments. Preliminary in vitro trials were conducted in order to investigate the mechanisms of action of L1 and L8 strains and in a dual culture dish assay, the antifungal effects observed on pathogen mycelium growth could be attributed to the production of volatile organic compounds (VOCs) generated by the antagonists. The VOCs significantly inhibited the growth of all three tested pathogens compared to the control, albeit with a different rate. When L1 strain was introduced into the wound 12 h from inoculum, it showed post-inoculation activity, the incidence of blue mould and bitter rot being reduced by 38% and 50% respectively, while the greatest inhibition of grey mould was observed when fruit were treated with the antagonist 6 h from the inoculum. In conclusion, A. pullulans L1 and L8 strains could be considered good candidates for the development of biofungicides for postharvest application in the pomefruit industry.

► A. pullulans strains were tested in the same study against three apple pathogens.
► The washed cells of antagonists controlled over 86% of decays.
► Antagonists isolated from carposhere of peach fruit showed good adaptation in apple.
► Some antifungal effects could be attributed to the volatile organic compounds.