Abstract: "Harvest 74-560 RZ F1" tomato was cultivated in a plant factory with LEDs. One of the four reproductive stages (flowering stage, expanding stage, color turning stage and harvesting stage) was subjected to low light intensity of 160μmol·m⁻²·s⁻¹, while the other three stages maintained 1000 μmol·m⁻²·s⁻¹. The light intensity kept 1000μmol·m⁻²·s⁻¹ at all the reproductive stages in the control. The growth and fruit quality indices were measured to evaluate the effects of low light on tomato. The results showed that: (1) low light significantly affected the morphology of tomato plants at the flowering stage and expanding stage. Low light at flowering stage resulted in the most prominent overgrowth trend of tomato plants, as well as the least average number of leaves and nodes per plant which respectively decreased by 3.5 and 1.6 compared with the control. Low light at the expansion stage significantly reduced the content of carotenoid and the value of Chla/b compared with the control. The number of fruit set per plant after low light treatment at flowering stage was 53% lower than that of the control, while the number of fruit set per plant was not significantly affected by low light at other reproductive stages. The average yield of the first, second and third ear per plant after low light treatment at flowering or expansion stage was significantly lower than the other treatments. (2) Compared with the control, low light treatments decreased the soluble solid content of tomato fruit (first ear) in varying degrees, among which, the soluble solid content decreased by 25% after low light treatment at flowering stage. The soluble sugar content of tomato fruit decreased by 15% compared with the control, on the contrary, the total acid content increased by 26%, resulting in the lowest sugar/acid ratio of tomato fruit under this treatment. Compared with the control, low light treatments decreased the vitamin C content of tomato fruit in varying degrees, among which, the lowest vitamin C content was detected in tomato fruit subjected to low light treatment at the harvesting stage. This study showed that low light reduced the yield and quality of tomato, and the sensitivity of tomato to low light was different at varied reproductive stages. According to the growth characteristics and responses of tomato subjected to low light at different periods, it is of certain significance to supplement artificial light in order to stabilize the quality and yield of protected tomato.

Key words: Tomato, Low light, Plant factory, Reproductive period, Fruit quality