Date of Award

6-2014

Degree Name

MS in Agriculture - Crop Science

Department/Program

Horticulture and Crop Science

Advisor

J. Wyatt Brown

Abstract

Fresh strawberries have grown into a multi-billion dollar industry over the last few decades in California. Botrytis cinerea or grey mold, is the worst pathological disorder affecting strawberry fruit causing cull rates of up to 30% in the worst seasons. Strawberry fruits are fragile and have a short shelf-life making timely harvest, cooling, and marketing an absolute necessity. The current industry standard is to ship strawberries in an overwrapped CO₂-enriched headspace pallet in refrigerated trucks at 33 °F. However, B. cinerea has the ability to grow at very low temperatures and continues to plague the strawberry industry during postharvest storage and retail sale.

Postharvest treatments available for strawberry preservation and disease management have been severely limited due to the reluctance to spray or wash the fruit. Consumers are also demanding produce that is free from synthetic chemical residues. Recent research with plant essential-oil volatile compounds has indicated that they have significant anti-fungal activity. Very little information is available regarding the use of essential-oil compounds for postharvest treatments on California strawberries to reduce the incidence of B. cinerea. The primary objective of this study was to investigate the potential for synergy to control B. cinerea through the combined application of volatile treatment constituents with uniquely different modes of action.

Strawberries were acquired from commercial growers in the Santa Maria area of California on the day of harvest. Volatile essential-oil compounds were diluted in ethanol and applied to sachets which were then affixed to the inner lids of randomly selected clamshells. Clamshells were individually overwrapped with a micro-perforated 1-mil polyethylene film. The marketable shelf-life, percent rotted fruit, headspace atmosphere, postharvest quality, and sensory analysis were determined during 14-21 days storage at 40°F.

The combination of ethanol (495.5 ppm), methyl jasmonate (4.5 ppm), citral (30 ppm), linalool (30 ppm), and vanillin (30 ppm) was the most effective formula to reduce rot and increase shelf-life overall and strawberries treated with 600 ppm of this blend maintained acceptable organoleptic quality. Applying high levels (750 ppm or more) of this formulation resulted in phytotoxic calyx desiccation after only 3 days at 40°F. However, moderate amounts (300-600 ppm per package) did not desiccate the calyx until 7-11 days of storage allowing sufficient time to market and consume the berries before the effect would be noticeable. A blend of essential-oil volatile compounds has the ability to significantly reduce postharvest losses from B. cinerea, can be applied without spraying on or washing fruit, and can be derived from natural sources.

Additional Index Words: Methyl jasmonate, carvacrol, thymol, citral, linalool, vanillin, Induced Acquired Resistance.

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