Blue light alters infection by Penicillium digitatum in tangerines

The effect of blue light exposure on Penicillium digitatum infection of tangerines during postharvest storage was investigated. In citrus, P. digitatum is one of the most important fungi causing diseases that result in postharvest loss. There is increasing interest in development of environmentally sustainable and consumer-friendly strategies of decay control. Strategies based on a plant's immunity can minimize pathogen infection of fruit. Light signalling affects plant-pathogen interactions and blue light may modulate phospholipase activation, a key step in plant immune responses. Exposure of fruit to 410-540 nm blue light at a fluency of 40 μmol m⁻² s⁻¹ reduced infection by P. digitatum and induced phospholipase A₂ (PLA₂) gene expression. Inhibition of PLA₂ activity allowed infection, whereas inhibition of phospholipase D (PLD) expression by 580-670 nm red light at the same fluency was correlated with infection. These data strongly suggest that induction of lipid signalling by light reduces fungal colonization by P. digitatum in citrus fruit.