Effect of salicylic acid and melatonin on chlorophyll fluorescence and initial growth of greenhouse tomatoes in salinity stress

The greenhouse crops recently attract enormous interest in Iran. The extensive greenhouse tomatoes cultivation, established for local and export markets. The salinity of irrigation water is one of limitation factors of greenhouse crops cultivation in arid and semi-arid regions. In this research, survey impact of melatonin and salicylic acid in reducing the destructive aspects of water salinity stress in the early stages of greenhouse tomato growth.

In a factorial split-plot experiment, tomato plants, Goldi cultivar, were exposed to salinity at 0, 50, and 100 mM NaCl as a main factor in hydroponic culture medium. Two sub-factors, Melatonin at 0, 10 μM and salicylic acid 0, 1.5 and 2.5 mM, were foliar sprayed in three time. Before flowerings, one month after transfer to the pot, shoot height and leaf length, leaf number and stem diameter were measured. Two months after planting, fruit weight, number of flowers per inflorescence and chlorophyll fluorescence parameters including minimum fluorescence (Fo), maximum fluorescence (Fm), variable fluorescence (Fv) and photochemical quantum yield (YII) were measured.

The results showed that salinity significantly reduced the vegetative and reproductive growth of tomatoes in greenhouse conditions but salicylic acid did not show a significant effect on vegetative and reproductive characteristics in the early stages of growth. Melatonin significantly increased the growth characteristics of tomato plants such as leaf length and number, plant height and stem diameter in the first month of growth (P <0.01). The results also showed that melatonin had a significant effect on increasing the number of flowers in the inflorescence and the number of fruits per plant in the two months after planting. Also, fluorescence parameters including Fm, Fo, Fv and YII showed a significant decreasing with increasing sodium chloride concentration (P <0.01). The average effective photochemical quantum efficiency of photosystem II decreased from 0.84 in non-stress conditions to 0.76 in salinity. Melatonin caused a significant increase (P <0.01) in the effective photochemical quantum efficiency of photosystem II and maximum and minimum fluorescence of tomato plants, but the application of salicylic acid had no effect on this parameters. The most effective photochemical of photosystem II was 0.84 in non-stress conditions and application of 10 μM melatonin.

The results of this study showed that salinity reduces the initial growth of tomato plants under greenhouse conditions. Salicylic acid did not show a significant effects on vegetative and reproductive characteristics in the early stages of tomato plant growth. Use of melatonin reduces the destructive effects of salinity and increases tomato tolerance to salinity in the early stages of growth.