Optimizing biomass allocation for optimum balance of seed yield and lodging resistance in rapeseed

Context Dense planting can boost achievable yields in rapeseed (Brassica napus L.). But it aggravates the lodging risk that is often associated with high–yielding cropping systems. Objectives This research aimed to assess the agronomic performance of rapeseed in terms of yield and lodging related attributes under various planting densities. Meanwhile, the effectiveness of electrical measurements i.e., root capacitance (EC) and impedance (EI) for predicting root morphology and lodging resistance was also evaluated. Methods This study comprised two rapeseed varieties (Qinyou7: a lodging susceptible; Shanyou28: a lodging resistant) which were grown in four planting densities (15, 30, 45 and 60 plants m–2) across four site-year environments. Data on various agronomic parameters were recorded including seed yield, root and stem morphology and lodging resistance. Results and conclusions With an increase in planting density from 15 to 60 plants m–2, the seed yields of variety Qinyou7 and Shanyou28 were increased by 67 % and 56 %, respectively. However, a tradeoff of seed yield with lodging resistance was evidenced in lodging susceptible variety Qinyou7. It tended to invest more biomass in the siliques to maximize seed yield, which led to reduced stem bending strength (Ss) and weaker root anchorage strength (Sr), thus making plants more prone to lodging (in terms of lower safety factor, SF). Conversely, the lodging resistant Shanyou28 allocated a greater amount of photosynthates to the stems and roots to enhance its lodging resistance by maintaining higher Ss and Sr, thus compromising on a part of its seed yield. Large diameter of the root–soil cone and robust roots can be considered as critical traits for selecting lodging resistant varieties due to their strong correlation with Sr, and other lodging associated root morphological traits. Both EC and EI measurements were closely linked with seed yield, root–related traits, and SF. Implications We strongly recommend exploiting these electrical measurements as a quick, low–cost, non-destructive, and efficient technique for predicting seed yield and lodging susceptibility of rapeseed.