LOD curves on Gm20 for daidzin among four environments. The curves indicate LOD scores of SLAF markers against their genetic position on Gm20. Different colours represent different environments (E1-E4). Red curve indicates the LOD curve in E1 (i.e. Changping in 2009), blue curve represents LOD curve in E2 (i.e. Shunyi in 2009), green curve indicates the LOD curve in E3 (i.e. Shunyi in 2010), and purple curve represents the LOD curve in E4 (i.e. Shunyi in 2011). The dashed line indicates the threshold LOD score.