Trampling-induced ethylene production delays spikelet initiation in spring wheat

Early sowing of spring wheat increases the risk of frost injury due to premature spikelet initiation under low temperatures. While trampling has been reported to delay spikelet initiation, its physiological mechanism remains unclear. We attempted to explain the delayed spikelet initiation caused by trampling in terms of the involvement of ethylene. The role of ethylene in trampling was investigated in the spring wheat cultivar Ayahikari by measuring ethylene production after trampling and applying the ethylene-releasing agent ethephon and the ethylene action inhibitor 1-methylcyclopropene (1-MCP). The effects of trampling and ethylene on the expression of VERNALIZATION1 ( Vrn1 ) and FLOWERING LOCUS T ( FT ), key regulators of spikelet initiation, were also examined. Trampling significantly increased ethylene production and delayed young spike development. Exogenous application of ethephon mimicked the effect of trampling on young spike development, while 1-MCP reversed this effect. Furthermore, trampling suppressed the expression of Vrn1 and FT , similar to the effects observed in ethephon-treated plants. The present study indicates that ethylene mediates the effect of trampling on young spike development likely through the suppression of Vrn1 and FT expression, ultimately causing a delay in spikelet initiation. Our findings provide a mechanistic explanation and highlight trampling as a potential agronomic strategy for mitigating frost risk in early-sown spring wheat.