Soybean Growth and Light Interception: Response to Differing Leaf and Stem Morphology

Altered canopy light environments created by plant architectural changes may increase plant productivity. Two morphological traits in soybean [ (L.) Merr.], brachytic stems (shortened internodes) and lanceolate leaflets, could be used for genetic manipulation of canopy structure. These traits were examined in various combinations in ‘Tracy-M’ (maturity group VI) and ‘Wright’ (maturity group VII) backgrounds in 1990 (two environments) and 1991 (one environment with two row width-plant population combinations). Throughout the season, plant height and photosynthetically active radiation (PAR) interception were monitored. At maturity, stem dry weight, seed yield, and yield components were determined. Brachytic stem genotypes were ≈40% shorter at harvest than the normal genotypes. Plant height was significantly associated with PAR interception during vegetative grown in both years ≥ 0.58), and during reproductive growth in wide rows at Clayton irrespective of year (≥ 0.66). In 1991, seed yield was positively related to PAR interception during reproductive growth in the wide row-low population combination (= 0.49), when all genotypes were included in the analysis. For the Tracy-M background, the same relationship was significant in all widerow environments. The data indicate that brachytic genotypes do not fully intercept available PAR in wide rows and low populations, especially when combined with lanceolate leaflets. Significant seed yield differences, despite 95% PAR interception by all genotypes in some environments, indicate the presence of yield limiting factors other than PAR interception. The present data fail to indicate significant improvements in performance due to the brachytic stem or lanceolate leaflet.