Effect of Short-Term, Above-Optimal Temperature on the Phenology of Partially or Fully Vernalized Seedlings and Its Consequences on Grain Yield in Wheat (Triticum aestivum L.)

Due to global climate change, short periods of unusually warm temperatures occur during winter and early spring with increasing frequency. Although temperature effects on wheat development have been extensively studied during later reproductive stages, the consequences of short-term warming during early development remain poorly understood. We investigated the effect of a short-term period of warm temperature on partially or fully vernalized wheat seedlings, with particular attention to their phenological characteristics and grain-yield formation. A total of 19 wheat varieties of diverse geographic origins were studied with known allele compositions in plant developmental genes of vernalization (VRN) and photoperiodic response (PPD). The experiment consisted of six treatments in factorial combinations of three low-temperature vernalizations (30, 45 and 60 days) followed by two temperature regimes (greenhouse and two-week 25 °C plus greenhouse) under long photoperiod. The effects of transient warming were strongly dependent on the degree of vernalization fulfilment. In fully vernalized winter wheat, warming generally accelerated development across genotypes, whereas after incomplete vernalization, it frequently delayed subsequent developmental transitions, particularly in photoperiod-sensitive cultivars. Variation in responses increased with decreasing vernalization saturation, indicating that allelic differences at flowering-time loci, including VRN and PPD, contribute to the integration of temperature signals during early development. Beyond phenology, transient warming strongly influenced tiller formation and reproductive tiller number. Following complete vernalization, warming increased fertile tiller production and resulted in higher grain yield, whereas responses after partial vernalization were genotype-dependent and less favorable. Comparison with previous controlled-environment experiments further demonstrated that thermal regime, rather than mean temperature alone, strongly influences tiller survival and yield formation. Short-term warming around the completion of vernalization can have long-lasting effects on wheat development and productivity, highlighting the importance of developmental stage, genetic background and environmental context in determining crop responses to increasingly variable winter temperatures.