Large-Scale Phenotyping of Root Traits in the Model Legume Lotus japonicus

Plants are sessile organisms that can tune their body architecture to the environment. This is very pronounced in their root system. In particular, nutrient availability strongly influences the architecture of the root system; depending on the abundance of specific nutrients, root growth rates and lateral root number are modulated. The extent of these effects is important for plant adaptation and has a major impact on plant fitness. However, the assessment of quantitative effects on a scale large enough for identifying genes and variants using quantitative genetics is difficult, and well-developed methods have been largely restricted to the model species Arabidopsis thaliana. In this chapter, we present a protocol for high-throughput phenotyping of early root traits in the model legume plant Lotus japonicus. This species allows for the study of important root-associated traits that are not present in Arabidopsis, such as symbioses with nitrogen-fixing Rhizobia and arbuscular mycorrhizal fungi. The methods described in this chapter can be used in the context of reverse and forward genetics approaches to dissect the genetic basis of root growth in legumes.