A review of new advances in mechanism of graft compatibility-incompatibility

The mechanism of graft incompatibility is not yet fully understood and many reports focus on this problem in order to understand the mechanisms of graft development. These reports refer to both cytological and biochemical responses occurring at an early phase in response to grafting, as well as the consequences of these events on the future graft response. Some theories argued the possibility that the phenomena of cellular recognition could be involved in the development of a functional vascular connection since the first callus are formed. However, callus formation can be a passive response to a wound with no implications in the future compatibility responses. We sum up different reasons that may have an influence on graft success: inherent system of cellular incompatibility, formation of plasmodesmata, vascular tissue connections, and the presence of growth regulators and peroxidases. In addition, phloem-mobile proteins have been reported that cross the graft interface when graft bridging is established and it is functional. This review provides an overview of the graft response and recent advances in the knowledge of the mechanism involved in the early responses to grafting for the development of cohesion between the stock and scion during graft ontogeny.