Light reflected from red mulch to ripening strawberries affects aroma, sugar and organic acid concentrations.

Strawberry (Fragaria ananassa) fruit size and flavor are important to both growers and consumers. Plastic mulches are frequently used in raised-bed culture to conserve water, control weeds with less herbicides, keep fruit clean and produce ripe berries earlier in the season. The most commonly used plastic mulch color is black. We hypothesized that changing mulch color to reflect more far-red (FR) and red light (R) and a higher FR/R photon ratio would keep those benefits and improve berry size and flavor by altering phytochrome-mediated regulation of pathways in ripening berries. Size and chemical composition of berries developed in sunlight over a specially formulated red plastic were compared with those that developed over standard black plastic mulch. Berries that ripened over red were about 20% larger, had higher sugar to organic acid ratios and emitted higher concentrations of favorable aroma compounds. We conclude that FR and the FR/R ratio in light reflected from the red mulch on the soil surface acted through the natural phytochrome system within the growing plants to modify gene expression enough to result in increased fruit size and improved concentrations of phytonutrient, flavor and aroma compounds.