Quantitative Characterization of Canopy Coverage in the Genetically Diverse Soynam Population.

Canopy development is critical to light interception by soybean throughout the growing season.  Rapid canopy closure facilitates complete light interception and optimizes growth dynamic parameters, which ultimately contribute to total biomass accumulation and grain yield.  The objective of this study was to assess the use of digital imagery as a phenotyping tool. Seasonal canopy coverage and light interception in the genetically diverse SoyNAM population was characterized. Weekly measurements of canopy coverage from early vegetative to mid reproductive growth were acquired for 5600 recombinant inbred lines during the 2013 and 2014 seasons.  An asymptotic logistic growth curve was fitted to the coverage data to estimate daily canopy coverage in intervals between the actual sampling dates and enable calculation of canopy dynamic parameters. Parameters evaluated in this study were: average canopy coverage (AC), cumulative intercepted photosynthetically active radiation for the total sampling period (CIPAR), vegetative growth period (CIPARv), and reproductive growth period (CIPARr), and the number of days required to reach 30 (t₃₀), 50 (t₅₀), and 70 (t₇₀) percent canopy coverage. Estimation of variance components revealed that phenotypic variation was significantly influenced by genetic differences among SoyNAM families for all canopy parameters.  The narrow-sense heritabilities of canopy parameters were high (h² = 0.81-0.90), and thus provide opportunities for genetic gain of canopy development through selection of superior genotypes. Strong genetic correlations to grain yield (r_g = 0.61-0.68) and high relative efficiencies of indirect selection (R_e = 0.76-0.84) suggest simultaneous genetic gain of yield and canopy parameters through a positive correlated response to selection.