High-density conditions trigger early GA activation and disrupt stem elongation–cell wall reinforcement coordination in rapeseed

The objective of this study was to identify developmental stages and regulatory factors underlying stem quality of rapeseed ( Brassica napus L.) under high-density planting. In two cultivars grown at low and high density, gibberellin (GA)-triggered early stem elongation was associated with delayed secondary cell wall deposition and reduced stem mechanical strength under high density. Foliar application of the GA biosynthesis inhibitor uniconazole at the 10–11 leaf stage delayed GA activation and slowed stem elongation, increasing stem mechanical strength and yield.