Abstract
Root system size is a key trait for improving water and nitrogen uptake efficiency in wheat (Triticum aestivum L.). This study aimed (i) to characterize the root system and shoot traits of five wheat cultivars with apparent differences in root system size; (ii) to evaluate whether the apparent differences in root system size observed at early vegetative stages in a previous semi-hydroponic phenotyping experiment are reflected at later phenological stages in plants grown in soil using large rhizoboxes. The five wheat cultivars were grown in a glasshouse in rhizoboxes filled to 1.0 m with field soil. Phenology and shoot traits were measured and root growth and proliferation were mapped to quantify root length density (RLD), root length per plant, root biomass and specific root length (SRL). Wheat cultivars with large root systems had greater root length, more root biomass and thicker roots, particularly in the top 40 cm, than those with small root systems. Cultivars that reached anthesis later had larger root system sizes than those that reached anthesis earlier. Later anthesis allowed more time for root growth and proliferation. Cultivars with large root systems had 25% more leaf area and biomass than those with small root systems, which presumably reflects high canopy photosynthesis to supply the demand for carbon assimilates to roots. Wheat cultivars with contrasting root system sizes at the onset of tillering (Z2.1) in a semi-hydroponic phenotyping system maintained their size ranking at booting (Z4.5) when grown in soil. Phenology, particularly time to anthesis, was associated with root system size.
Highlights
There is no consensus on whether root system size in wheat is critical for improving water and nitrogen uptake, despite the common assumption that large root systems capture more water and nitrogen and produce more biomass and greater yields [1,2]
The cultivars with large root systems (Ghurka and Bahatans-87) had 24% more leaf area than those with small root systems (Tincurrin and Hartog) (Table 3)
Wheat cultivars with large and small root systems at early vegetative stages (Z2.1) of growth in a semi-hydroponic system maintained the size of their root system at later stages
Summary
There is no consensus on whether root system size in wheat is critical for improving water and nitrogen uptake, despite the common assumption that large root systems capture more water and nitrogen and produce more biomass and greater yields [1,2]. Genotypic variation in wheat root system size exists [3,4], providing the opportunity to improve water and nutrient uptake efficiency in cereal crops [5,6,7]. Whether the size of the root system is a candidate trait for improving water and nitrogen uptake efficiency needs investigation. As a first step, wheat genotypes with putative differences in root system size need to be identified and characterised. It is assumed that a large root system requires more photosynthetic assimilates for its production, proliferation, growth and function. It has been estimated that the amount of photosynthetic assimilates invested to produce one unit of root dry matter can produce double that of shoot dry matter [9]
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