Control of Penicillium digitatum on “Tarocco” orange by combined application of Pseudomonas syringae and resistance inducers

Penicillium digitatum is the causal agent of green mould (GM) of citrus fruit that often causes extensive decay losses during storage and transportation, thus limiting the commercial life of harvested fruits. Accordingly, sustainable control strategies may prevent postharvest diseases and may be a useful alternative to pesticide applications. The aim of this study was to evaluate the effectiveness of Pseudomonas syringae strain 48SR2 (BCA), sodium bicarbonate (SBC) heated to 45°C, acibenzolar-Smethyl (ASM) and chitosan, applied alone and in combination, on ‛Tarocco’ oranges artificially inoculated with P. digitatum 24 h before, simultaneously, and 24 h after treatments. Combinations of BCA+SBC and BCA+ASM applied 24 h before pathogen inoculation (preventive activity) totally inhibited pathogen growth and the combination of treatments improved the protection provided by treatments alone. In addition, combinations of BCA+chitosan applied as preventive treatments significantly reduced incidence and severity of GM but no synergistic effect was detected. BCA+SBC simultaneously applied with the pathogen effectively controlled GM of ‘Tarocco’ oranges, whereas treatments applied alone were less effective. In general, treatments applied 24 h after pathogen inoculation (curative activity) were not effective. These experiments suggest that P. syringae biocontrol agent in combination with resistance inducers and salts could be considered a recommended approach to improve pest management strategies in citrus packinghouses.