The growth period and earliness of cotton (Gossypium spp.): phenological architecture, environmental and genetic regulation, and breeding perspectives

The growth period of cotton ( Gossypium spp.), spanning emergence to boll opening, is a highly complex quantitative trait governed by genetic potential, thermal accumulation, photoperiodic sensing, resource availability, and agronomic management. Optimizing developmental duration and enhancing earliness are essential for mitigating grain-cotton land competition, enabling mechanized harvesting, and strengthening climate resilience. This review synthesizes current advances in cotton phenology, earliness genetics, and developmental regulation across six key domains. We first detail principal phenological stages and standardized BBCH staging systems based on a systematic literature synthesis following PRISMA principles. Next, we examine thermal and environmental drivers, focusing on growing degree days, photoperiodic responses, and resource dynamics highlighting subgenome-biased expression. We then outline the genetic architecture of earliness, integrating two decades of bi-parental QTL mapping, fine-mapping, meta-QTL analyses, and multi-environment GWAS alongside structural variants predominantly on chromosomes D03, D08, and A10, such as pericentric inversions revealed by telomere-to-telomere assemblies. Furthermore, we delineate the multi-layered molecular and epigenetic networks governing floral induction, centered on the FT-FD-14-3-3 florigen activation complex (FAC), upstream miR157-SPL and HD-Zip I regulators, and histone and DNA methylation dynamics, while establishing rigorous distinctions between true physiological earliness and premature senescence. We also deliberate agronomic management and chemical regulation levers alongside physiological source-sink trade-offs. Finally, we critically assess prospective biotechnological tools, including CRISPR/Cas promoter fine-tuning, genomic selection (GS), high-throughput phenomics, and crop simulation modeling to overcome traditional yield-quality penalties and break linkage drag.