Effects of 1-Methylcyclopropene on Rice Growth Characteristics and Superior and Inferior Spikelet Development Under Salt Stress

Salinity stress hampers rice growth and development due to its osmotic, ionic, and hormonal (ethylene) stresses. High ethylene production affects inferior and superior spikelet development in rice cultivars under salt stress. 1-Methylcyclopropene (1-MCP) is an excellent ethylene inhibitor in plants. However, the effects of 1-MCP on rice growth and spikelet development under salt stress have not been studied. In this experiment, two rice cultivars, Liangyoupeijiu (LYP9, indica) and Nipponbare (NPBA, japonica), were grown in a pot culture experiment with three levels of salt stress [control (CK), 1.5 g NaCl/kg dry soil (low salt stress, LS), and 4.5 g NaCl/kg dry soil (heavy salt stress, HS)] and two 1-MCP levels (no 1-MCP and 1-MCP applied at the rice booting stage) over ten sampling times. The results showed that the application of 1-MCP significantly inhibited ethylene production in inferior spikelets of both cultivars compared with superior spikelets under salt stress. 1-MCP is more effective in increasing grain-filling rate and grain weight for inferior spikelets than for superior spikelets in both cultivars. The application of 1-MCP improved the net photosynthesis rate (Pₙ), stomatal conductance (gₛ), transpiration rate (Tᵣ), SPAD values, and the leaf area index (LAI) of flag leaves in both cultivars compared with no 1-MCP application. 1-MCP was more effective in increasing grain-filling rate and grain weight in the LYP9 cultivar than in the NPBA cultivar under all salt stress treatments. As compared to the treatment without 1-MCP at the same salt stress level, the grain yield per plant with 1-MCP treatment increased by 35.6, 37.6, and 35.3% for CK, LS, and HS treatments, respectively, for LYP9 plants. 1-MCP treatment increased the rice grain-filling rate, plant dry matter, and yield components, such as 1000-grain weight, grain formation rate, and harvest index, of both NPBA and LYP9. These findings demonstrate the beneficial role of 1-MCP under salt stress by increasing rice growth characteristics and the development of spikelets, particularly inferior spikelets.