Canopy Photosynthesis and its Association with Seed Yield in Advanced Generations of a Soybean Cross

Canopy‐apparent photosynthesis (CAP) of soybean, Glycine max (L.) Merr., plants during reproductive development differs among genotypes, is a heritable trait, and is positively associated with seed yield. These responses collectively imply a potential for yield improvement through selection for enhanced CAP. This research was undertaken to: (i) determine if the CAP response patterns of F4 lines remain relatively stable in F6 lines, (ii) determine the association CAP to yield and growth characteristics in F6 lines, and (iii) identify F6 lines with similar maturity and divergent CAP. The experiments were conducted over a 2‐yr period at Athens, GA under field conditions. A l‐min measurement of CAP was made near mid‐day in all plots for three times during reproductive development by use of a closed system and ambient conditions. Other measurements included plant height, stages of plant development, seed wt., length of seed‐fill period, and seed yield. The upper 50% of the F4 lines averaged 11% higher in CAP than the lower 50%. The F6 lines derived from the high CAP F4 lines were 6% (0.9 μmol CO2 m−2 s−1) higher in CAP than F6 lines from the low F4 lines. There was an association between CAP of F4 lines and the mean of the F6 lines derived from them (r = 0.64; P < 0.I). A positive association was found between CAP and seed yield (r = 0.28 to 0.66). Pairs of F6 lines with divergent CAP rates but similar maturity were identified. Results support previous findings that CAP during reproductive development is positively associated with seed yield in determinate soybean genotypes.