Stability of Cry3Bb1 protein in soils and its degradation in transgenic corn residues

As the land area planted with transgenic crops expressing insecticidal proteins from Bacillus thuringiensis (Bt) continues to increase, and more farmers adopt reduced and no-till practices, the quantity of residues remaining in the fields that may contain Bt proteins is likely to increase considerably. We evaluated the potential of the Cry3Bb1 protein, active against the corn rootworm, to persist in soils with various pH and clay contents at seven sites in NY, USA under different climate conditions, where 15 Bt corn varieties were grown. The within seasonal dynamics of the Cry3Bb1 protein in soils and its decomposition in Bt corn residues were assessed in detail over two years at one site in Aurora, NY, USA. Results showed that soils with higher clay contents had lower Cry3Bb1 extraction efficiencies, but greater protein persistence; while pH was not correlated with any of them. The protein persistence in soils was also inversely correlated with the precipitation. In Aurora, NY, USA, the Cry3Bb1 protein was detectable in rhizosphere soils at anthesis, but not at planting and was barely detectable at pre-harvest. The Cry3Bb1 protein varied in its concentration among different types of transgenic corn residues, lowest in roots, and decomposed nearly completely after 3.5 months. Overall, soil clay content and precipitation were important for the stability or detection of the Cry3Bb1 protein in tested soils. The rapid decomposition of the Cry3Bb1 protein in corn residues and its short persistence in soils indicate that the exposure level of Cry3Bb1 protein to soil-dwelling organisms is likely to be low and transitory. However, the low concentration of Cry3Bb1 protein in roots may hasten the evolution of pest resistance and cause economic losses.