Figure 3. Detection of Bt genes by PCR in DNA samples derived from soil cultivated with transgenic (Pucara TD -event 176- and 32G63MG -event MON810-) and nontransgenic (Pucara and 30F82) maize. Lanes 1-5, three months interval sampling of soil starting from the crop before harvest (February, May, August, November 2002 and March 2003, respectively). +, positive control. -, negative control. M, molecular marker.