Spectral high-throughput assessments of phenotypic differences in biomass and nitrogen partitioning during grain filling of wheat under high yielding Western European conditions

Grain filling, the last phase of final yield development, is characterised by the transfer of assimilates and nitrogen compounds from vegetative plant tissues (source) to grains in the spike (sink). In this study, we spectrally assessed source and sink components to characterise the grain filling of wheat cultivars. In 2009, six high-yielding wheat (Triticum aestivum L.) cultivars were grown and fertilised with 160kgnitrogenha^-1. At four development stages during grain filling, the crops were sampled to determine the phenotypic variation in dry weight translocation as well as in the nitrogen uptake of the spikes and of the leaves combined with the stems. The final grain yield and grain N content was assessed, and the grain dry matter content was calculated as the ratio of the dry weight to the fresh weight. The harvest index was further calculated. At each sampling date, tractor-based high-throughput canopy reflectance measurements were carried out, and multiple vegetation indices were calculated. Spikes characteristics were best related to the final grain yield. While the water index, R₉₇₀/R₉₀₀, explained the biomass partitioning between spikes and vegetative plant parts, the NIR/NIR-based index, R₇₆₀/R₇₃₀ described nitrogen partitioning and the spikes dry matter with an r² of up to 0.89. The final grain dry matter was best assessed by spectral indices offering information about physiological maturity. The cultivars strongly differed in yield relevant crop traits, as illustrated by their relative ranking of the crop traits. Observing yield relevant crop traits by spectral reflectance may allow to rapidly and non-destructively classify cultivars with regard to source-sink relationships.