Postharvest β-aminobutyric-acid–primed resistance is not effective in the control of Penicillium expansum Link. on ‘Golden delicious’ apple fruit

β-Aminobutyric acid (BABA) can induce resistance in several plant species and protects them from various pathogens. Previous investigations have been shown that BABA induce resistance responses also in apple fruit and protects them against Penicillium expansum Link., the agent of the apple blue mold. However, this protection does not appear to be related to the induced defenses. To verify this hypothesis, we here investigated the effects of BABA treatment on the induction of resistance on ‘Golden delicious’ apple fruit, and evaluated in vivo the protective effects of the induced resistance against P. expansum. At 48 h post-treatment, 2 × 10−2 mol L−1 BABA treatment induced accumulation of the PR-1a and LOX-1a gene transcripts and deposition of callose. According to the priming phenomenon, the levels of the induced genes and callose were significantly higher in apple fruit pretreated with 2 × 10−2 mol L−1 BABA and inoculated with P. expansum, with respect to noninoculated BABA-pretreated fruit. The lack of protection of apple fruit pretreated with 2 × 10−2 mol L−1 BABA and rinsed before inoculation showed that the induced resistance by itself did not limit the pathogen. Instead, protection observed on treated apple fruit rinsed before inoculation confirmed the direct antimicrobial activity of BABA against P. expasnum. Although induction of resistance is reported to be a promising tool also in post-harvest control of fruit pathogens, the real importance of the induced defenses in the fruit protection against pathogens needs to be evaluated by an experimental design that separates the antimicrobial and inductive effects of a treatment.