Additional Blue LED during Cultivation Induces Cold Tolerance in Tomato Fruit but Only to an Optimum

Abstract

Tomato is a chilling-sensitive fruit. The aim of this study is to examine the role of preharvest blue LED lighting (BL) to induce cold tolerance in 'Foundation' tomatoes. Blue and red supplemental LED light was applied to achieve either 0, 12 or 24% additional BL (0B, 12B and 24B). Mature green (MG) or red (R) tomatoes were harvested and cold stored at 4 °C for 0, 5, 10, 15 and 20 d, and then stored for 20 d at 20 °C (shelf life). Chilling injury (CI) indices, color and firmness, hydrogen peroxide, malondialdehyde, ascorbic acid and catalase activity were characterized. At harvest, R tomatoes cultivated at 12B were firmer and showed less coloration compared to fruit of other treatments. These fruits also showed higher loss of red color during cold storage and lower CI symptoms during shelf-life. MG tomatoes cultivated at 12B showed delayed coloring (non-chilled) and decreased weight loss (long cold stored) during shelf life compared to fruit in the other treatments. No effects of light treatments, both for MG and R tomatoes, were observed for the selected antioxidant capacity indicators. Improved cold tolerance for R tomatoes cultivated at 12B points to lycopene having higher scavenging activity at lower concentrations to mitigate chilling injury.

Keywords: blue LED; chilling injury; lycopene; tomato fruit.

Figure 1

Average decay index with indicated standard error during shelf life (20 °C) for five red (R) tomatoes per cold storage duration. Red, green and blue symbols indicate cultivation at 0, 12 and 24% additional blue light, respectively. Tomatoes were either non-stored (A) or cold stored at 4 °C for 5 d (B), 10 d (C) or 20 d (D). LSD values, when present, are indicated per panel.

Figure 2

Average color at harvest (A), expressed as normalized anthocyanin index (NAI) and (B) firmness, expressed as FI index, at harvest of twenty-five MG (solid bars) and R tomatoes (dashed bars) with indicated standard error, respectively. Colors indicate tomatoes cultivated with 0 (red bars), 12 (green bars) and 24% (blue bars) additional blue light. The different letters in each panel indicate significant differences between light treatment.

Figure 3

Average color, firmness and weight loss development of five MG tomatoes during shelf life at 20 °C after cold storage at 4 °C for 0 d (A,E,I) 5 d (B,F,J), 10 d (C,G,K) or 20 d (D,H,L) with indicated standard error, respectively. Colors indicate tomato cultivation with 0 (red symbols), 12 (green symbols) and 24% (blue symbols) additional blue light. LSD values, when present, are indicated per panel.

Figure 4

Average color development, expressed as NAI values (A), and average firmness development, expressed as FI index (B), for five red tomatoes during cold storage (4 °C), with indicated standard error. Red, green and blue symbols indicate cultivation with 0, 12 and 24% additional blue light, respectively. The LSD value in panel A indicates the presence of significant differences between light treatments.

Figure 5

Changes in total AsA (A), CAT activity (B), H₂O₂ (C), and MDA (D) content at harvest and cold storage (4 °C) for fifteen MG (green symbols) and fifteen R tomatoes (red symbols). Light treatment effects were not significant and therefore values are shown only per maturity. LSD values are indicated per panel.