The effect of discontinuous blue light intervention on red-light-grown tomato fruit coloration

Micro Tom tomatoes were cultivated in a plant factory to investigate the effect of discontinuous blue light intervention on the coloration process of tomato fruit grown under red light. Five treatments were set up, namely R (continuous pure red light), R 6h /RB 2h (pure red light for 6 h and then blue light intervention for 2 h, the same below), R 4h /RB 4h , R 2h /RB 6h , RB (simultaneous irradiation of red and blue light). Based on fruit color spectral parameters, the influence of discontinuous blue light on fruit pigmentation was evaluated by measuring pigment contents, key enzyme activities, and the expression levels of related genes. The results showed that: (1) At color break stage (47 days after anthesis, DAA), an increase in the a* (20.7 %) and Red/Green (29.8 %) was observed in tomato fruits exposed to R 6h /RB 2h compared to R. In contrast, L*, Hue and MCARI were decreased by 9.4 %, 15.3 % and 74.6 % respectively, indicating that the tomato fruits were redder under R 6h /RB 2h . (2) At color break stage, the contents of lycopene, α-carotene, lutein and zeaxanthin in fruits subjected to R 6h /RB 2h were increased by 3.1 %, 11.1 %, 3.9 % and 8.8 %, respectively, relative to R, resulting in orange-red tomato fruits. (3) Compared to R, the activities of phytoene synthase, phytoene desaturase, ζ-carotene desaturase, lycopene β-cyclase and lycopene ε-cyclase in fruits under R 6h /RB 2h were increased by 6.2 %, 9.8 %, 18.5 %, 2.6 % and 1.9 % at color break stage, respectively. Furthermore, the expression of key carotenoid biosynthetic genes GGPS, PSY, PDS, ZDS, LCY-B and LCY-E were upregulated under R 6h /RB 2h . (4) Correlation analysis revealed that Mg and Ca were positively correlated with PSY, GGPS, PDS, ZDS , and lycopene, suggesting that discontinuous blue light intervention might regulate fruit coloration by affecting the absorption of mineral elements in tomatoes. In summary, in terms of tomato fruit coloration, short-term discontinuous blue light intervention (R 6h /RB 2h ) could maximize the positive effects of single red light and mixed red-blue light on tomato fruit coloration under the same photoperiod. This study provided an effective light supply strategy for regulating the light environment of tomato coloration in industrial production.