Adventitious Shoot Regeneration and Agrobacterium tumefaciens-mediated Transient Transformation of Almond 3 Peach Hybrid Rootstock 'Hansen 536'

'Hansen 536' (Prunus dulcis 3 Prunus persica) is an important commercial rootstock for peach and almond. However, susceptibility to wet soil and bacterial canker has limited its use primarily to areas with less annual rainfall. Genetic engineering techniques offer an attractive approach to improve effectively the current problems with this cultivar. To develop an efficient shoot regeneration system from leaf explants, 10 culture media containing Murashige and Skoog (MS) or woody plant medium (WPM) supplemented with different plant growth regulators were evaluated, and adventitious shoot regeneration occurred at frequencies ranging from 0% to 36.1%. Optimal regeneration with a frequency of 32.3% to 36.1% occurred with WPM medium containing 8.88 mu M 6-benzylamino-purine (BAP) and 0.98 to 3.94 mu M indole-3-butyric acid (IBA). The regenerated shoots had a high rooting ability, and 80% of the in vitro shoots tested rooted and survived after being transplanted to substrate directly. Transient transformation showed an efficient delivery of the beta-glucuronidase (GUS) reporter gene (gusA) using all three Agrobacterium tumefaciens strains tested with a concentration of OD600 0.5 to 1.0 for 4 days of cocultivation. The protocols described provide a foundation for further studies to improve shoot regeneration and stable transformation of the important peach and almond rootstock 'Hansen 536'.