Effect of salicylic acid on biocontrol efficacy of Pseudomonas fluorescens against blue mold of apple fruit

Blue mold, caused by Penicillium expansum, is a major postharvest disease of apple fruits.This study was conducted to evaluate the efficacy of salicylic acid at various concentrations alone or in combination with Pseudomonasfluorescens to control the postharvest blue mold of apple fruit and investigated its possible modes of action through the measurements of salicylic acidon induction of biochemical defense mechanisms.salicylic acidat the concentration of 1000 µg ml-1 significantly inhibited the spore germination of P. expansumin vitro, but it was not effective in controlling the disease in vivo.Simultaneous application of salicylic acidand P.fluorescens showed that the biological efficacy of P.fluorescens against P. expansum on apple fruit could be significantly enhanced by adding salicylic acid, which was most effective at 10 µg ml-1 but less effective at a higher or lower concentrations. Fruits treated with salicylic acidor P.fluorescens alone had significantly higher phenolic content and proxidase activity than the control fruits but the combination of P.fluorescens with salicylic acidat 10 µg ml-1also had a synergistic effect on the induction of fruit resistance to the disease.