Canopy Photosynthesis and Seed-Fill Duration in Recently Developed Soybean Cultivars and selected Plant Introductions

Canopy photosynthesis and seed-fill period have been shown to be positively related to seed yield in soybean [Glycine max (L.) Merr.]. The present study was undertaken to identify recently developed cultivars (RC) and plant introductions (PI) with high canopy-apparent photosynthesis (CAP) or long seed-fill period and to determine the relationship of these traits to seed yield in these genetically diverse genotypes. Twenty genotypes in Maturity Groups (MG) VI, and VII were grown on an Appling course sandy loam soil (Typic Haplndult, clayey, kaolinitic, thermic) near Athens, GA, for 2 yr. The genotypes consisted of seven RC, seven PI, which had been previously identified as having high seed yield, three high photosynthetic cultivars (HPC), and three low photosynthetic cultivars (LPC). Five CAP measurements were taken during the reproductive stage of development. When averaged over maturity groups, the RC were 5% higher in CAP than the LPC and 13% higher than the PI. The RC and HPC had 4 to 5 days longer seed-fill period than PI or LPC. The RC averaged 12% higher in seed yield then the LPC and 6% higher than PI. In MG V, PI157440 and the RC ‘Deltapine 345’ had CAP rates higher than the LPC ‘Dare’ and equal to the HPC ‘Forrest’. In MG VII, ‘GaSoy 17’ had a CAP rate above the HPC ‘Bragg’. Partial correlation coefficients with the effect of maturity removed were positive between seed yield and CAP (r = 0.63), seed-fill period (r = 0.54), and the product of CAP and seed-fill period (r = 0.78). These results indicate that high photosynthetic capacity and long seed-fill period were associated with high seed yield in this diverse group of genotypes. Contribution from Dep. of Agronomy, Univ. of Georgia. This research was supported by state and Hatch funds allocated to the Georgia Agric. Exp. Stn., the Georgia Agric. Commodity Commission for Soybeans, and by the USDA/SEA under a grant from CSRS.