Effect of Growth Stage and Pod Position on Soybean Seed Isoflavone Concentration

Field experiments were established during 2004 at two sites of the Emile A. Lods Agronomy Research Centre in Sainte-Anne-de-Bellevue, QC, Canada. Soil types were a fine sandy loam at one site (site A) and a Macdonald clay loam at the other (site B). During seed development and maturation, three replicates of 200 pods were collected from different parts of plants (from the top and base of plants) at three development stages; full-seed pod (R6), yellow pod (R7) and brown pod (R8), resulting in 6 treatments. Total and individual isoflavone concentrations were determined by high-performance liquid chromatography. Our results indicate that the individual and total isoflavone contents were significantly influenced by growth stage and pod position, The maximum individual and total isoflavone contents were recorded when the soybean seeds were collected from the base parts of plants at brown pod stage (R8). The maximum protein content of 468 g kg(-1) was obtained by collecting soybean seeds at the earlier growth stage (R6). Also, the soybean seeds developing at the top parts of plants accumulate a greater amount of protein than those from the base region. On the other hand, soybean seeds developing at the base parts of plants (first 20 cm from soil surface) accumulate greater amount of oil than those from the top (last 20 cm from soil surface).