Quantitative characterization of canopy coverage in the genetically diverse soynam population
Despite estimates of annual on-farm soybean (Glycine max L. Merr.) grain yield gain ranging from 23-66 kg ha-1 yr -1, current trends show that the average decadal increase of soybean grain yield is declining in rate. It is suggested that a narrowing genetic diversity of cultivated soybean germplasm due to direct selection for grain yield, and insufficient knowledge of genetic influences underlying grain yield-associated physiological traits are contributing factors. Canopy development plays a critical role in the fraction of light intercepted by soybean crops throughout the growing season. Rapid canopy closure maximizes 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 ground-based digital imagery as a phenotyping tool for quantitative characterization of seasonal canopy coverage and light interception in the genetically diverse SoyNAM population. Weekly measurements of canopy coverage from early vegetative to mid reproductive growth were acquired for 5600 recombinant inbred lines during the 2013 and 2014 season. 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 showed that variation in phenotypic expression was significantly influenced by genetic differences among families for all canopy parameters. The narrow-sense heritabilities of all 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 (rg = 0.61-0.68) and high relative efficiencies of indirect selection (Re = 0.76-0.84) suggest simultaneous genetic gain of grain yield and canopy parameters through a positive correlated response to selection.
Rainey, Purdue University.
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