Growth and Yield of Soybean Lines Selected for Divergent Leaf Photosynthetic Ability1

Abstract

One way to enhance net photosynthate production in soybean [Glycine max (L.) Merr.] may be to breed genotypes with accelerated leaf photosynthetic rates. The objective of this experiment was to determine the effects of divergent selection for 14CO2‐uptake rate per unit leaf area, total photosynthesis (TPs), on seed yield and canopy growth. Eighteen F7‐derived lines were grown in the field. These included nine lines previously selected for rapid TPs and nine selected for slow TPs. Total photosynthesis was measured during the seed filling period in 1979 and 1980. The lines were not all at the same growth stage on a given sampling date, so the average TPs rate over the 30 d period after the beginning of seed filling was calculated. This average (MTPs) equals the estimated area under the curve describing TPs as a function of time over the 30 d period, divided by 30 d. The TPs groups differed (P<0.01) in MTPs (2.51 vs. 2.29 nmol/s cm2, averaged over three locations and 2 years). TPs groups did not differ in seed yield, crop growth rate, harvest index, or the duration of seed filling. Seed yield was not correlated with MTPs among the nine lines within either group. Crop growth rate was not consistently correlated with TPs (as measured on any single date) among lines within groups. The TPs groups had similar seed yields in 1981. We concluded that selection for rapid TPs, as measured on a single light‐saturated leaflet, may not lead to greater seed or dry matter yields in soybeans.