Biocontrol of postharvest blue mould rot of pear by Cryptococcus laurentii

Summary

Cryptococcus laurentii was evaluated for its activity in reducing postharvest blue mould decay of pear caused by Penicillium expansum. Washed cell suspensions of yeast controlled blue mould better than yeast in culture broth. Treatment of wounds with autoclaved cultures or cell-free culture filtrate did not prevent decay. There was a negative correlation between concentrations of the yeast cells and infectivity of the pathogens: at concentrations of yeast at or above 1 × 10⁹ colony forming units (CFU) ml^–1 and pathogen spores suspension of 5 × 10⁴ spores ml^–1, blue mould was completely inhibited after 7 d of incubation at 25°C, and was almost inhibited after 30 d incubation at 2°C followed by 7 d at 20°C. The interval between inoculation with the pathogen and application of the antagonist significantly influenced the efficacy of biocontrol. Efficacy was maintained when C. laurentii was applied simultaneously or prior to inoculation with P. expansum but reduced if applied after inoculation with P. expansum. Rapid colonization of the yeast in wounds was observed during the first 3 d at 20°C, and then the populations stabilized for the remaining storage period. On pear wounds kept at 4°C, the increase in population density of C. laurentii was lower than at 20°C, but rose over 15 d after application of the antagonist to approx. 10⁷ CFU wound^–1.