Supplementary lighting is commonly used in high-quality seedling production. In this study, grafted tomato seedlings were grown for 10 days in a glasshouse with 16-h daily supplementary lighting at 100 μmol·m⁻²·s⁻¹ PPFD (Photosynthetic photon flux density) from either high-pressure sodium (HPS), metal halide (MH), far-red (FR), white LEDs (Light emitting diodes) (W), or mixed LEDs (W₁R₂B₁, where the subscript numbers indicate the ratio of the LED chips) to determine which light sources improve the seedling quality. The control seedlings did not receive any supplementary light. Physiological parameters and the expression of genes related to photosynthesis were analyzed. The results showed that root length, biomass, number of leaves, chlorophyll (SPAD), scion dry weight to height ratio (WHR), and specific leaf weight (SLW) were the greatest for grafted seedlings grown in W₁R₂B₁. The level of root ball formation was the greatest for seedlings grown in W₁R₂B₁, followed by those grown in W, HPS, and MH. Seedlings grown in FR did not fare well, as they were very thin and weak. Moreover, the expression of two photosynthetic genes (PsaA and PsbA) was significantly increased by W₁R₂B₁ and W, which suggests that the plastid or nuclear genes might be regulated. The overall results suggest that W₁R₂B₁ was the most suitable light source to enhance the quality of grafted tomato seedlings. The results of this study could be used as a reference for seedling production in glasshouses, and may provide new insights in the research on lights affecting the development of plants.

The effects of the quality and intensity of night interruption light (NIL) on the flowering and morphogenesis of kalanchoe (Kalanchoe blossfeldiana) ‘Lipstick’ and ‘Spain’ were investigated. Plants were raised in a closed-type plant factory under 250 μmol·m⁻²·s⁻¹ PPFD white light emitting diodes (LEDs) with additional light treatments. These treatments were designated long day (LD, 16 h light, 8 h dark), short day (SD, 8 h light, 16 h dark), and SD with a 4 h night interruption (NI). The NIL was constructed from 10 μmol·m⁻²·s⁻¹ or 20 μmol·m⁻²·s⁻¹ PPFD blue (NI-B), red (NI-R), white (NI-W), or blue and white (NI-BW) LEDs. In ‘Spain’, the SPAD value, area and thickness of leaves and plant height increased in the NI treatment as compared to the SD treatment. In ‘Lipstick’, most morphogenetic characteristics in the NI treatment showed no significant difference to those in the SD treatment. For both cultivars, plants in SD were significantly shorter than those in other treatments. The flowering of Kalanchoe ‘Lipstick’ was not affected by the NIL quality, while Kalanchoe ‘Spain’ flowered when grown in SD and 10 μmol·m⁻²·s⁻¹ PPFD NI-B. These results suggest that the NIL quality and intensity affect the morphogenesis and flowering of kalanchoe, and that different cultivars are affected differently. There is a need to further assess the effects of the NIL quality and intensity on the morphogenesis and flowering of short-day plants for practical NIL applications.

Supplementary lighting is commonly used in high-quality seedling production. In this study, grafted tomato seedlings were grown for 10 days in a glasshouse with a 16-hour daily supplementary lighting at 100 μmol·m−2·s−1 PPFD from either high pressure sodium (HPS), metal halide (MH), far-red (FR), white LEDs (W), or mixed LEDs (W1R2B1) to determine which light sources improve the seedling quality. The control did not have any supplementary light. The physiological parameters and the expression of genes related to photosynthesis were analyzed. The results show that the root length, biomass, number of leaves, chlorophyll (SPAD), dry weight to height ratio (WHR) of the scion, and specific leaf weight (SLW) were the greatest for grafted seedlings grown in W1R2B1. The level of root ball formation was the greatest for seedlings grown in W1R2B1, followed by those grown in W, HPS, and MH. Seedlings grown in FR did not fare very well, as they were very thin and weak. Moreover, the expression of two photosynthetic genes (PsaA and PsbA) was significantly increased by W1R2B1 and W, which suggests that the plastid or nuclear genes might be regulated. The overall results suggest that W1R2B1 was the most suitable light source to enhance the quality of grafted tomato seedlings. The results of this study could be used as a reference for seedling production in glasshouses, and provide new insights in the research of lights affecting the development of plants.