SOYBEAN GROWTH AND LIGHT INTERCEPTION - RESPONSE TO DIFFERING LEAF AND STEM MORPHOLOGY

Altered canopy light environments created by plant architectural chang es may increase plant productivity. Two morphological traits in soybea n [Glycine mar (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 'Tra cy-M' (maturity group VI) and 'Wright' (maturity group VII) background s in 1990 (two environments) and 1991 (one environment with two row wi dth-plant population combinations). Throughout the season, plant heigh t and photosynthetically active radiation (PAR) interception were moni tored. At maturity, stem dry weight, seed yield, and yield components were determined. Brachytic stem genotypes were almost-equal-to 40% sho rter at harvest than the normal genotypes. Plant height was significan tly associated with PAR interception during vegetative grown in both y ears R2 greater-than-or-equal-to 0.58), and during reproductive growth in wide rows at Clayton irrespective of year (R2 greater-than-or-equa l-to 0.66). In 1991, seed yield was positively related to PAR intercep tion during reproductive growth in the wide row-low population combina tion (r2 = 0.49), when all genotypes were included in the analysis. Fo r the Tracy-M background, the same relationship was significant in all wide-row environments. The data indicate that brachytic genotypes do not fully intercept available PAR in wide rows and low populations, es pecially when combined with lanceolate leaflets. Significant seed yiel d differences, despite 95% PAR interception by all genotypes in some e nvironments, indicate the presence of yield limiting factors other tha n PAR interception. The present data fail to indicate significant impr ovements in performance due to the brachytic stem or lanceolate leafle t.