Evaluate the sensitivity of rapeseed lodging under low light：A field study on the biomechanics of stem and root lodging in rapeseed (Brassica napus L.)

Solar dimming has been increasing and threatening crop production in rapidly developing regions (China). The low light stress caused by reduced radiation affects rapeseed production. Lodging is one of the main causes of yield loss and quality decline in rapeseed. However, few studies have been conducted so far on the mechanisms of shade effects on rapeseed lodging. This study aims to investigate the effects of low light on the lodging resistance, structural and biomechanical characteristics of four rapeseed genotypes and determine which lodging type (stem and root lodging) is more common under low light stress based on actual lodging conditions in the field. Shading net was used to investigate the bending strength of stems and root-related parameters. The results showed that low light significantly reduced stem and root lodging resistance, manifested as a decrease in stem bending strength and root anchoring strength, respectively. low light significantly reduced stem diameter (12.6 %) and second moment of area (37 %). low light also reduced stem anatomical parameters, especially cortical thickness (5.4 %) and lignin area (24.9 %). The significant reduction in root length, root diameter, root depth, root bending strength, and root tip strength leads to a shallower root layer, thereby affecting the root anchoring strength. Differences in root plane coverage area and root-soil cone volume exist between genotypes. low light reduced the safety factor of stem and root, but the decrease in root safety factor was higher. Besides that, lodging ratio data showed that, root lodging is more likely to occur under low light treatment as compared to stem lodging. The results of this study indicate that under low light stress, especially in low light areas, rapeseed genotypes with strong roots and high anchoring strength should be selected to improve lodging resistance.