Phenotyping the hidden half – roots as breeding targets

Phenotyping is the current bottleneck to accelerate plant breeding (Fiorani and Schurr, 2013), and new methods are needed for root phenotyping, with the aim to select for root systems with increased water and nutrient acquisition. Subsequently, breeding targets are root system architecture, nutrient acquisition and metabolic efficiency (Lynch and Wojciechowski, 2015). We developed and used several root phenotyping pipelines to identify root traits that reduce abiotic stress in waterlogged or low nutrient environments. Results of the waterlogging study show that tolerant genotypes had a faster root and shoot development in the seedling stage and developed more nodal roots during the waterlogging treatment compared with sensitive genotypes. The study also found a higher percentage of aerenchyma in nodal roots and a narrow stele in both seminal and nodal roots of tolerant genotypes suggest that these traits may contribute to increased tolerance during waterlogging (Sundgren et al., submitted). Studies of root cortical senescence (RCS) of barley varieties demonstrated genetic variation exists for the rate of RCS development. Nitrogen and phosphorus deficient environments increased the rate of RCS development. RCS decreases the metabolic cost of root tissue, reducing root nitrogen and phosphorus content by 65% and respiration by 87% compared to root segments of the same length with no RCS. Older root segments with complete RCS had 89% less radial water, nitrate, and phosphorus transport compared to younger root segments with no RCS. RCS was associated with 30% greater aliphatic suberin content in the endodermis (Schneider et al., 2017). Ethylene application significantly accelerated RCS development and ethylene synthesis and signalling genes were significantly upregulated during the onset of RCS (Schneider et al., submitted). For field grown barley plants, we developed a phenotyping platform that allows the phenotyping of root crown architectures and the effects of a low nitrogen environment on architectural root traits. These studies show that phenotyping enables the discovery of root traits that potentially facilitate tolerance of abiotic stresses and may be included in future plant breeding programs.Key words: root architecture, root anatomy, phenotyping, novel root trait