The curious origins of a high-stress training technique mainlining: its molecular, biochemical, and agronomic perspectives for the cultivation of Cannabis sativa

Mainlining is a high-stress training (HST) technique utilized in Cannabis sativa cultivation to restructure plant architecture, enhance canopy uniformity, and increase inflorescence yield. Despite its widespread application, scientific literature detailing the possible molecular, physiological, and agronomic mechanisms underlying this method remains limited. This review consolidates current knowledge on mainlining, focusing on its origins and its interaction with apical dominance, shoot apical meristem (SAM) regulation, and vascular differentiation. The technique involves strategic decapitation to disrupt apical dominance, initiating hormonal and metabolic shifts-particularly in auxin and sugar signalling-that stimulate axillary bud outgrowth and promote symmetrical cola development. Mainlining integrates both low- and high-stress training methods, including topping, lollipopping, and tie-downs, to optimize light distribution, canopy structure, and resource allocation. Further emphasis is placed on the role of vascular remodeling and secondary cell wall development in plant recovery and structural reinforcement following stress. The review also identifies critical research gaps, such as the absence of standardized protocols across Cannabis subspecies, and outlines future directions involving omics technologies, AI-assisted cultivation, and precision breeding. This synthesis provides a foundational reference for aligning empirical cultivation practices with plant developmental biology, contributing to the advancement of evidence-based Cannabis horticulture.