Characterization of the Genotypic Diversity of Root System Architecture in Winter Oilseed Rape (Brassica napus) in Response to Nitrogen Availability, Using the ArchiSimple Model

To develop sustainable agriculture, improving the ability of plants to efficiently use available nitrogen becomes a major issue. For winter oilseed rape (WOSR), known to have high nitrogen requirements, an important breeding challenge is to create new varieties with improved Nitrogen Use Efficiency. To reach this aim, one key lever relies on the optimization of the root system architecture (RSA). However, direct high-throughput phenotyping of root traits is still difficult and limited to very young stages. To bypass this lock, models of RSA make it possible synthesizing dynamic architecture from a number of input parameters (traits) and could therefore be a powerful tool to screen genotype diversity.The aim of our study was to characterize the RSA of several WOSR genotypes and their plasticity in response to nitrogen availability, by using the RSA ArchiSimple (Pagès et al, 2014, Ecol Modell) model parameters as screening traits.

To experimentally estimate the ArchiSimple model parameters, several contrasted genotypes of WOSR were grown in long pots for 800 to 1000 degree-days under two levels of nitrogen availability (either limiting plant growth or not). After plant excavation, roots were separated from shoots, cleaned and scanned at high resolution. ArchiSimple parameters relative to root diameter, elongation rate and branching characteristics were measured at the individual root level, using the ImageJ and SmartRoot softwares. In addition, shoot and root biomasses were measured at the plant scale. The RSA of each genotype was simulated with ArchiSimple and under both N conditions. The evaluation was based on the ability of the model to predict root length and biomass dynamics.

Results of experiments and simulations pointed out the RSA parameters exhibiting genotypic variability and/or plasticity in response to nitrogen availability for WOSR. Moreover, a sensitivity analysis allowed the quantification of the impact of these trait variations at the whole-plant level.