2018 ASHS Annual Conference

Micro-grafting, an increasingly popular method, involves grafting an aseptic scion onto an in vitro-grown rootstock. Success of micro-grafting is largely depended on firm contact between rootstock and scion at the graft junction, which will assist the callus formation. Micro-grafting procedures are difficult due to the fact of handling difficulties associated with preserving the delicate graft unions. In this study, we used a root-predominant gene promoter (SbUGT) to drive the expression of a tryptophan-2-mono oxygenase gene (iaaM) from Agrobacterium tumafaciens to increase auxin levels in tobacco rootstock. Our results have showed that over-expression of the iaaM gene in rootstock enhance vascular formation in stem tissues. In our micro-grafting experiments, we have observed that grafting joints using the SbUGT::iaaM rootstock are tighter in junctions than the wild type plant rootstock, and therefore higher success rate of micro-grafting are observed. Also, compared with wild type plant rootstock, we have observed that the stem cuttings of SbUGT::iaaM rootstock plants can root quicker. Furthermore, the expression of iaaM gene in rootstock suppresses their lateral bud releases while growth of scions is not affected. Thus, the SbUGT::iaaM gene may be a useful tool for improving rootstock and subsequently enhancing success rates of micro-grafting for many crop plant species.