Development of Novel, Antimicrobial Plant Essential Oil Treatments to Reduce the Postharvest Incidence of Botrytis cinerea on Strawberries

Strawberry fruits are very fragile and have an extremely short shelf-life, making timely harvest, cooling, and marketing of the fresh fruits absolute necessities.  Botrytis cinereaor gray mold continues to plague the strawberry industry both in the field and during postharvest storage, shipment, and retail sale.  Postharvest treatments available for berry preservation and disease management have been limited due to the reluctance to spray or wash the berries.  Little information is available regarding the use of volatile essential-oil compounds for postharvest treatments on California strawberries to reduce the incidence of grey mold.  Strawberries were obtained from commercial growers in the Santa Maria area of California.  Volatile compounds were diluted in ethanol and applied to sachets affixed to the inner lids of clamshells, with one sachet per clamshell.  Clamshells were individually overwrapped with a microperforated 1-mm polyethylene film to prevent excessive CO₂ buildup within the packages.  The marketable shelf-life, percentage of rotted fruit, postharvest quality, and levels of oxygen and CO₂within the packages were determined during 14 days storage at 40 °F. Strawberries treated with both methyl jasmonate (MJ) and ethanol (ETOH) had less rot and a longer shelf-life than the untreated control (UTC) fruit or those treated with MJ or ETOH alone suggesting a synergistic effect.  A mixture of 3.5 µL MJ + 300–600 µL ETOH combined with 25-100 µL citral (CT) + 25-100  µL linalool (LN) or 100 µL carvacrol (CV) + 0.05 g thymol (TY) + 100 µL eugenol (EU) reduced rot and increased shelf-life significantly compared to the UTC, ETOH, or methyl jasmonate treatments; however, these combinations were found to be phytotoxic to both the strawberry calyx and the fruit when overall volume of essential oils per clamshell were 200 μl or higher.  ETOH had a positively-correlated and rate dependent effect on strawberry respiration that lasted through the storage period.  The combination of 400-600 µL ETOH + 25-50 µL CT + 25-50 µL LN + 3.5 µL MJ was most effective at reducing rot and increasing shelf-life compared to the UTC, and this combination did not affect organoleptic quality.