Evaluation of the Mitigating Effect and Application Efficacy of Melatonin Applied at the Seedling Stage on Short-Term Chilling Stress in Tomato Plants

To address the short-term chilling stress that frequently occurs in horticultural facilities under adverse meteorological conditions, this study investigated the impact of exogenous melatonin on the cold resistance of tomatoes in facilities, aiming to provide a theoretical basis for the application of melatonin in production.

Seedlings of Solanum lycopersicum cv. ‘Hezuo909’ were used as the experimental material and treated with either clear water or 200 μmol·L^-1 melatonin solution via root irrigation. Five days after treatment, half of the seedlings from each group were subjected to low-temperature stress（12 ℃/7 ℃, day/night）for 12 days, while the remaining seedlings were maintained under normal temperature conditions. During the treatment period, morphological traits, chlorophyll fluorescence parameters, photosynthetic pigment contents, and mineral element concentrations were measured in each treatment group. After the 12-day temperature treatment at the seedling stage, all seedlings were transplanted into a solar greenhouse with uniform growth conditions, and subsequent monitoring was conducted for morphological parameters, phenological stages, yield components, and fruit quality attributes.

Chilling during the seedling stage led to a decrease in the content of photosynthetic pigments in tomato seedling leaves, a weakening of photosynthetic performance, hindered absorption of mineral elements, and inhibited plant growth. The impact of chilling during the seedling stage persists throughout the entire growth period, resulting in a prolonged lag in growth rate of tomato plants after transplanting compared to the control group under normal temperature, extended phenological phases, and reduced yield. The exogenous application of melatonin enhanced the absorption capacity of N, P, K, and Fe elements in tomato seedlings, mitigated the decline in photosynthetic pigment levels, maintained the photosynthetic performance of the leaves, and significantly alleviated the inhibitory effect of chilling on the growth of tomato seedlings. Additionally, the application of melatonin promotes the recovery and growth of tomato seedlings after transplanting.

Chilling during the seedling stage inhibited the growth of tomato seedlings, and the adverse effects persisted throughout the entire growth period after transplanting. The application of melatonin effectively mitigated the adverse effects of chilling on the growth and development of tomatoes by regulating nutrient uptake and maintaining the photosynthetic performance of leaves.