Huazhong Agricultural University researchers reveal how high-density planting disrupts stem development in rapeseed

Rapeseed (Brassica napus L.) is an important global oilseed crop and a major source of vegetable oil. Increasing planting density can improve yield potential and facilitate mechanized harvesting. However, excessive density intensifies competition for light and resources, resulting in weaker stems, reduced mechanical strength, and increased lodging risk. Although high-density lodging has traditionally been linked to shading and resource competition, how high density disrupts the coordination between stem elongation and structural reinforcement remains poorly understood.

Researchers from the Rapeseed Cultivation Physiology Team at Huazhong Agricultural University have now provided new insights into this question. Their study, published in The Crop Journal, reveals that high-density planting triggers early gibberellin (GA) activation, accelerating stem elongation while delaying structural reinforcement.

“We found that high-density planting does not simply restrict stem development. Instead, it alters the timing of GA activation, causing stem elongation to occur ahead of structural reinforcement,” shares corresponding author Associate Professor Jing Wang. “This temporal mismatch provides new insight into why stems become weaker under high-density conditions.”

In two-year field trials with the conventional cultivar ZS11 and hybrid cultivar HYZ50, the team compared low-density (3.0 × 10⁵ plants ha^-1) and high-density (6.0 × 10⁵ plants ha^-1) planting. Stem elongation in both cultivars occurred mainly from budding to initial flowering, with high-density planting further increasing the contribution of this period to final plant height while reducing stem mechanical strength. Analysis of 243 accessions further showed that a greater proportion of height gain during this stage was negatively correlated with mature stem bending strength, particularly under high-density conditions.

The researchers then examined the underlying mechanism. “Transcriptomic and physiological analyses showed that high density triggered earlier GA activation, followed by rapid stem elongation, whereas cellulose and lignin accumulation and mechanical reinforcement lagged behind,” says Wang. “High-density plants also showed reduced cellulose and lignin contents, lower cellulose crystallinity, and weaker stem bending strength.”

To further verify the role of GA, the researchers applied the GA biosynthesis inhibitors uniconazole and DPC under field conditions. Uniconazole reduced endogenous GA levels, restrained excessive stem elongation, and promoted cellulose and lignin accumulation, thereby improving stem bending strength and tissue density. Importantly, it also improved yield under high-density conditions, increasing per-plant yield by 9.4% in ZS11 and 10.8% in HYZ50, and yield per unit area by 7.0% and 6.6%, respectively.

“The improvement in both stem strength and yield following GA regulation is particularly encouraging,” Wang says. “Optimizing GA dynamics during critical developmental stages may help achieve a better balance between plant architecture, lodging resistance, and yield under high-density cultivation.”

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Author contact:

Jing Wang, wangjing@mail.hzau.edu.cn.

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