As root electrical capacitance (CR*) was assumed to depend on the stem properties, the efficiency of measuring CR* at flowering for whole-plant phenotyping was assessed in five wheat cultivars in three replicate plots over two years. Linear regression analysis was used to correlate CR* with plant-size parameters and flag-leaf traits (extension and SPAD chlorophyll content) at flowering, and with yield components at maturity. The plot-mean CR* was correlated with the plot leaf area index (LAI), the chlorophyll quantity (LAI×SPAD), and the grain yield across years. At plant scale, CR* was found to show the strongest positive regression with total chlorophyll in the flag leaf (flag leaf area × SPAD; R2: 0.65−0.74) and with grain mass (R2: 0.55−0.70) for each cultivar and year (p < 0.001). Likewise, at plot scale, the regression was strongest between CR* and the LAI×SPAD value (R2: 0.86−0.99; p < 0.01) for the cultivars. Consequently, CR* indicated the total plant nutrient and photosynthate supply at flowering, which depended on root uptake capacity, and strongly influenced the final yield. Our results suggested that the polarization of the active root membrane surfaces was the main contributor to CR*, and that the measurement could be suitable for evaluating root size and functional intensity. In conclusion, the capacitance method can be applied for nondestructive whole-plant phenotyping, with potential to estimate root and shoot traits linked to the nutrient supply, and to predict grain yield. CR* can be incorporated into allometric models of cereal development, contributing to optimal crop management and genetic improvement.
Keywords: flag leaf; grain yield; in situ root methods; nutritional status; root activity.