ASHS 2025 Conference

Consumers want year-round supply of high quality fresh produce. However, the low sunlight has limited greenhouse vegetable during the winter months in high-latitude region. In order to boost yields and meet market demand, supplemental lighting is required. However, utilizing electric lighting, even high-efficient LED fixtures results in high electricity costs. Photoperiod extension (up to 24h) is a promising strategy which can be implemented in many countries as the utility companies incentivize the use of low cost, off-peak electricity use during the night. In this way, extending the photoperiod from the conventional 16h up to 24h can result in reduced electricity cost when the daily light integral (DLI) remains the same. In this study, we look at the impact of two different 24h lighting strategies in two cherry tomato cultivars and their impact on photoperiod injury compared to a 16h control. One 24h treatment involved a change from white light during the day to blue light at night at a reduced photosynthetic photon flux density (PPFD; i.e., dynamic) while the other kept a static spectrum and PPFD for 24h. In addition, each treatment also had a low blue (10%) and high blue (30%) variation. The experiment took place in a glass greenhouse at the Harrow Research and Development Centre in Harrow, Ontario, Canada. It was determined that the 24h dynamic lighting strategy has similar maximum quantum yield of photosystem II (Fv/Fm) values as the 16h controls while the 24h static treatments values were drastically reduced. What’s more, the Fv/Fm value from the 24h static treatment with high blue content was lowest among all treatments indicating that elevated levels of blue light may be detrimental during a 24h photoperiod. In addition, the overall yield from the 24h dynamic treatments were similar to the 16h controls while the 24h static treatments were statistically lower. Taken together, these results indicated that a 24h dynamic light treatment is essential to mitigate photoperiodic injury in cherry tomato. This data suggests that the use of such a lighting strategy could also reduce electricity costs for greenhouse cherry tomato producers.