Moderate delayed sowing increases grain number per spike by escaping low temperature stress and optimizing post-jointing temperature of winter wheat in Southwest China.

Global warming has increased the intensity and frequency of extreme low temperature events. Winter wheat in Southwest China lacks an overwintering dormancy period and undergoes an earlier and prolonged jointing stage, rendering it highly vulnerable to jointing-stage freezing injury. This study aimed to explore whether adjusting sowing date (SD) via delayed sowing could mitigate freezing injury at the jointing stage in Southwest China. A two-year field experiment was carried out with the winter wheat cultivar Shumai 1963 with five sowing dates, including early sowing (October 23, S1), normal sowing (October 30, S2), and late sowing (November 6, S3; November 13, S4; November 20, S5). The results showed that moderate sowing delay (7-14 days) prolonged the vegetative growth period and postpones the onset of jointing of wheat, thus effectively avoiding the risk of freezing injury. A 7-14-day sowing delay significantly improved grain yield by increasing grain number per spike (GNPS). Further analysis revealed that delayed sowing elevated the daily mean temperature (MT) from jointing to anthesis, reduced spikelet abortion and significantly increased fertile spikelets and grains across basal, central and apical spike positions. Benefiting from improved spike development, S3 and S4 raised grain yield by 4.0%-17.0% and significantly enhanced harvest index (HI) and effective accumulated temperature use efficiency (TUE) relative to normal sowing (S2). In conclusion, postponing sowing by 7-14 days is a feasible agronomic practice to evade spring low temperature, optimize post-jointing thermal environment and improve wheat productivity in Southwest China under climate warming.