THE EFFECT OF SELECTION PRESSURE ON TRANSFORMATION FREQUENCY AND COPYNUMBER IN TRANSGENIC PLANTS OF TALL FESCUE (FESTUCA-ARUNDINACEA SCHREB)

Protoplasts of Festuca arundinacea (Schreb.) were transformed with pla smids containing a hygromycin resistance gene, and plants were regener ated under a variety of selection regimes. Plant regeneration was high est under discontinuous selection, but resulted in the production of s ignificant numbers of escapes. Continuous selection at low concentrati ons of hygromycin produced the highest numbers of transgenic plants wi thout escapes. Transgene copy numbers for 83 plants were estimated and related to the selection regime under which the plants were regenerat ed. Discontinuous application of hygromycin produced a high proportion of plants containing two or fewer inserted copies of the transgene (8 7%), as did low levels (50 mg . l(-1)) of continuous selection on hygr omycin (88%). Continuous selection at high concentrations of hygromyci n biased selection in favour of multiple-copy containing plants. Using a plasmid encoding a hygromycin phosphotransferase enzyme of higher s pecific activity (pROB5) resulted in the production of significantly m ore transgenic plants.