Botrytis cinerea response to pulsed light: Cultivability, physiological state, ultrastructure and growth ability on...

Botrytis cinerea causes postharvest spoilage in important crops such as strawberry and other berries. Pulsed light (PL) treatment could be an environmentally friendly postharvest alternative to synthetic fungicides in berries. Cultivability, physiological state, ultrastructure of Botrytis cinerea suspended in peptone water and irradiated with PL (fluence = 1.2 to 47.8 J/cm²) were investigated by using conventional plate count technique, flow cytometry analysis (FCM) and transmission electron microscopy. In addition, PL effect on B. cinerea development in artificially contaminated strawberries throughout storage at (5 ± 1) °C was evaluated. PL reduced fungus' ability to form colonies on agarized culture media. Survival curve fitted with the Weibullian model evidenced a wide distribution of conidia sensitivity to PL. FCM showed that most of irradiated conidia entered in a viable non-culturable state, although a subpopulation without esterase activity and compromised membranes and a subpopulation with active esterase and intact membranes were also detected. PL attacked multiple targets in B. cinerea. Ultrastructural changes varied with the dose and within the conidia population, supporting FCM results. Damage included plasmalemma detachment from cell wall, cytoplasm collapse, and vacuolization of cytoplasm, disruption of cell wall and plasmalemma with massive loss of cytoplasm and/or disruption of organelles. In strawberries artificially contaminated with B. cinerea, a 2-day delay on the onset of the infection and a lower incidence in PL-treated strawberries (11.9 and 23.9 J/cm²) compared to control (16-20%) up to 10 days of cold storage was observed. Results indicated that PL significantly reduces B. cinerea growth in peptone water and in inoculated strawberries. However, other preservation factor(s) in combination would be needed to increase PL action for a better control of this fungus.