Engineering of Herbicide‐Resistant Alfalfa and Evaluation under Field Conditions

The recent development of gene transfer systems for higher plants and progress in identifying genes encoding important agronomic traits have opened new possibilities for improvement of crop species. Our objectives were to establish a transformation procedure for alfalfa (Medicago saliva L.) line RA‐3 using Agrobacterium‐mediated T‐DNA transfer on stem and petiole discs, compare the applicability of three selectable marker genes, and introduce a trait conferring resistance to a broad‐spectrum herbicide. Fifty‐nine transgenic lines carrying the bialaphos resistance gene bar encoding resistance to the herbicide glufosinate‐ammonium [ammonium‐DL‐homoalanin‐4‐yl (methyl) phosphinate] were analyzed under greenhouse and field conditions. The plants expressing bar under control of the cauliflower mosaic virus CaM V35S promoter showed the highest levels of resistance, whereas plants carrying bar under control of the TDNA TR2' promoter generally exhibited only a tolerance under field conditions. Our data clearly demonstrate the necessity of combining molecular analysis and field evaluation of individual transgenic lines.