Effects of low temperature stress at booting stage on yield and physiological characteristics in two wheat cultivars with contrasting cold sensitivity

To investigate the response mechanisms of different wheat organs to low‑temperature stress at the booting stage and the genotypic variation in cold tolerance, pot‑grown plants of a cold‑sensitive cultivar (Fengdecunmai 5, FC5) and a cold‑tolerant cultivar (Yunong 907, YN907) were subjected to ‑6 °C for 2 h (T1), 4 h (T2), and 6 h (T3). Antioxidant enzyme activities, osmolyte levels, membrane lipid peroxidation, photosynthetic parameters, and chlorophyll fluorescence were systematically measured in young spikes and flag leaves. Yield and its components were determined at maturity. The key findings were as follows: (1) Organ‑specific response strategies were revealed: young spikes maintained higher soluble sugar content, and malondialdehyde (MDA) decreased by 11.33%-24.56%, indicating an osmotic‑adjustment‑based stability strategy. In contrast, flag leaves exhibited increased MDA (2.65%-16.02%) and marked proline accumulation (up to 91.76% under T3), reflecting a typical reactive‑oxygen‑species scavenging and osmotic‑protection mode. (2) Principal component analysis (cumulative contribution 65.20%-89.62%) visualized a continuous spectrum of cold tolerance: YN907 showed "robust" tolerance, with clustered physiological states, high and stable antioxidant enzyme activity; FC5 displayed "stress‑responsive" sensitivity, with dispersed physiological states, severe membrane damage, and a bottleneck in antioxidant response under prolonged stress. (3) The 6‑h treatment (T3) caused irreversible damage to the photosynthetic system: net photosynthetic rate (Pn) and maximum photochemical efficiency (Fv/Fm) in both cultivars failed to recover to control levels even 10 days after stress, with more severe inhibition in FC5. (4) Yield analysis showed that low‑temperature stress significantly reduced spike number and grains per spike (FC5 decreased by 47.13% under T3), while thousand‑kernel weight increased significantly (FC5 increased by 23.58% under T3), indicating a source‑sink‑driven compensatory effect that could not fully offset yield loss. In summary, the two cultivars exhibited clear organ-specific strategies and contrasting physiological characteristics in response to low-temperature stress at the booting stage. The tolerant cultivar YN907 achieved effective cold resistance by maintaining physiological homeostasis and multi-system coordination. This study provides new insights into the physiological mechanisms underlying differential cold tolerance between two contrasting wheat genotypes and offers a foundation for future research aimed at breeding low temperature resistant cultivars. • Young spikelets and flag leaves employ distinctly different physiological strategies to cope with low-temperature stress. • Cold-tolerant and sensitive varieties exhibit two distinct tolerance patterns: “robust” and “stress-responsive” types. • Severe low-temperature stress during the heading stage can cause irreversible damage to the photosynthetic system of wheat. • The compensatory increase in thousand-grain weight cannot fully offset the yield loss caused by reduced panicle number and grains per panicle.