Increasing Ascorbic Acid Content of Strawberries by Cultivation methods and Postharvest Light Treatments.

MSc-thesis abstract (submitted 10 September 2015): Research on Ascorbic Acid (Vitamin C, AsA) has increased in the last decade as its multiple benefits on human health have been stressed by scientists. Strawberries are, not only one of the fruits with the highest concentration of AsA, but also one of the model plants for investigating the different pathways of AsA biosynthesis. Increasing the AsA content of strawberries would therefore: Benefit consumers for health related issues, become a strong marketing tool for growers and provide new insights on AsA biosynthesis and regulation.

Two preharvest and two postharvest experiments using cultivars ‘Elsanta’, ‘Clery’ and one postharvest experiment with ‘Favori’ were conducted.
The preharvest experiments, carried in the greenhouses of “Dings Aardbeien”, consisted of (1) flower removal (0, 25 and 50%) in combination with regulated water deficit (100, 80, 60% water supply) and (2) application of Salicylic Acid (spray or drench).
The postharvest experiments, carried in a climate chamber, consisted of (1) light irradiance of fruits at different intensities (0, 8, 300 and 600 μmol m-2 s-1) during 3 and 6 days for ‘Elsanta’ and 2 and 4 days for ‘Clery’ as well as (2) postharvest Botrytis cinerea incidence on fruits from the preharvest combination of of flower removal with regulated water deficit. The postharvest experiment with ‘Favori’ consisted of light irradiance at 0 and 600 μmol m-2 s-1 measured every day during 5 days.

Results of the most extreme flower removal (FR) and regulated water deficit (RDI) combination (50% FR and 60% water supply) showed an increase of approximately 24% in AsA concentration in comparison to the control for both cultivars.
The application of SA as a spray increased AsA by 13% for ‘Elsanta’ but had no effect for ‘Clery’.
Postharvest light irradiance had no effect in general, but a significant increase in AsA was achieved during the first days of fruit ripening and a decrease after several days postharvest. No relationship between increased AsA concentration and postharvest Botrytis cinerea incidence was found.

The results of the preharvest experiments suggest that the combinative effect of oxidative stress and increased assimilates has a stronger effect than the individual effects.
The results of postharvest experiments suggested significant AsA biosynthesis during fruit ripening and a posterior decay associated with water loss.
These two different effects can be directly related to the two most important pathways known for AsA biosynthesis but the extent to which each one acts and their interaction is yet to be understood.
Further research including gene expression and enzymatic analysis is therefore suggested.