Changes in peroxidase and phenols activity in apple fruit inoculated with antagonistic Pseudomonas fluorescens isolates and Botrytis mali.

The biocontrol activity of three isolates of Pseudomonas fluorescens against gray mold of apple fruit caused by Botrytis mali and their ability to induce biochemical defense response in apple tissue were investigated. Apple fruit (Malus domestica) wounds were inoculated with 20 microL bacterial suspension (10(8) CFU mL(-1)) of Pseudomonas fluorescens followed 24 h later by 20 microL of conidial suspension of B. mali (10(5) conidia mL(-1)). The apples were then incubated at 20 degrees C for 11 days. Lesion diameters were evaluated 6 and 10 days after pathogen inoculation. In addition to controlling gray mold, these three isolates of P. fluorescens caused increase in peroxidase activities that reached maximum levels 2-6 days after pathogen inoculation. Phenolic accumulation was increased in apple fruit treated with antagonists and inoculated with B. mali and exhibited the highest level 6-8 days after treatment. The ability of P. fluorescens to increase activities of peroxidase and levels of phenol compounds maybe one of mechanism responsible its biocontrol activity.