ANTIBIOTIC CONSTRUCT IN GMOs. “Researchers have expended much energy and resources into developing alternative transgenic plant production schemes such as herbicide tolerance, positive selection, and marker-free selection. All these alternatives have prominent drawbacks. After all, approximately 70% of all transgenic plants have been produced using the neomycin phosphotransferase II (nptII) gene from Escherichia coli for good reason: it works, especially in most dicot species.”
http://www.isb.vt.edu/articles/oct0501.htm