The physiological mechanisms underlying glyphosate resistance in wild soybean germplasm and relevant
EPSPS gene expression were evaluated. These germplasms were selected by gradually increasing glyphosate
selection pressure started from 2010. As indicated by a whole-plant dose response bioassay, ZYD-254
plants were resistant to glyphosate at concentrations of 1230 g ae ha1, but the susceptible plants (ZYD-
16) were unable to survive in the presence of 300 g ae ha1 glyphosate. The ED50 values of resistant germplasm
were approximately 8.8 times of the susceptible germplasm. Chlorophyll content was significantly
decreased in ZYD-16 plants in comparison with ZYD-254 plants. ZYD-16 plants accumulated 10.1 times
more shikimate in leaves at 5 days after glyphosate treatment at 1230 g ae ha1 than ZYD-254 did. GST
activity differed between ZYD-254 and ZYD-16 in three tissues. It was highest in leaves. There were no
significant differences in EPSPS1 or EPSPS3 expression between two germplasms before exposure to glyphosate
treatment. After glyphosate treatment, there was a 2- to 4-fold increase in EPSPS1 mRNA levels in
ZYD-254, but there was no change in EPSPS3 mRNA levels in ZYD-254 or ZYD-16.