Evaluation of a herbicide-resistant trait conferred by the bar gene driven by four distinct promoters in transgenic blueberry plants

Four chimeric bialaphos resistance (bar) genes driven by different promoters were evaluated for production of herbicide-resistant 'Legacy' blueberry plants (73.4% Vaccinium corymbosum L. and 25% Vaccinium darrowi Camp) through Agrobacterium tumefaciens (Smith & Towns.) Conn.-mediated transformation. When the bars were used as selectable marker genes, different promoters yielded different transformation frequencies. Three chimeric bar genes with the promoter nopaline synthase (nos), cauliflower mosaic virus (CaMV) 35S, or CaMV 34S yielded transgenic plants, whereas a synthetic (AocS)(3)AmasPmas promoter did not lead to successful regeneration of transgenic plants. In addition, herbicide resistance in bar-expressing plants was influenced by the promoter strength. Under controlled environmental conditions, 3-month-old plants from six single-copy transgenic events with 35S::bar or nos::bar, as well as those nontransgenic plants, were sprayed with herbicide glufosinate ammonium (GS) at five levels (0, 750, 1500, 3000, and 6000 mg.L-1). Evaluations on leaf damage 2 weeks after spraying indicated that all transgenic plants exhibited much higher herbicide resistance than nontransgenic plants. Additionally, the transgenic plants with the 35S::bar showed a higher herbicide resistance than those with the nos::bar. After application of 6000 mg-L-1 GS, over 90% of the leaves from plants with the 35S::bar and 19.5% to 51.5% of the leaves from plants with the nos::bar showed no symptom of herbicide damage, whereas only 5% of leaves from the nontransgenic had no damage. One-year-old, field-grown plants from four transgenic events with the nos::bar were evaluated for herbicide resistance after spraying with 750 mg.L-1 GS. Transgenic plants survived with variations in the level of foliar damage; in contrast, all nontransgenic plants died. This study is the first investigation of different promoters for engineering transgenic blueberry plants.