A conserved flowering-time module underlies double-season cropping

Adapting crops to intensive cultivation systems under climate change requires varieties that combine yield potential with optimized flowering and maturation^1,2. In central and eastern China, barley has long been cultivated in a double-season cropping system, in which early flowering and maturation are critical for escaping presummer terminal heat stress and enabling flexible rotation with summer crops^3,4. Here we trace the genomic footprints of 80 years of modern breeding in China using 505 representative cultivars and identify a flowering-time module defined by a single amino acid substitution in PHYTOCHROME C in combination with a winter-type VERNALIZATION 1 haplotype that underpins this adaptation. The derived allele accelerates heading and maturity, and its frequency has risen sharply in modern autumn-sown varieties. Using base editing in barley and wheat, we confirm causality and demonstrate that this flowering-time combination module, PhyC-VRN1, is functionally conserved across Triticeae. Our results identify and experimentally validate a breeding-relevant flowering-time module that has been selected during modern breeding to enable intensive crop rotations, as well as demonstrate how precision genome editing can be used to reconstruct such adaptive modules for climate-resilient crop design.