In recent years almond production has increased due to the strong tendency of consumers towards plant-based products. The grafting propagation method is the most widely used for this Prunus species to increase production and fruit quality. During grafting, the plant vasculature is severely damaged thus affecting auxin transport. However, once the scion and the rootstock join, a complex process involving cell division and differentiation of vascular tissues establishes communication between the two parts. Nevertheless, wound healing and auxin-induced regulatory mechanisms involved in scion-rootstock interactions remain largely unknown. Thus, this work aimed to quantify and immunolocalize IAA (indole-3-acetic acid) in almond trees micrografts, before and 21 days after micrografting, an in vitro technique that allows a rapid graft union formation using in vitro established scions and rootstocks.

To achieve this goal, scions and rootstocks were in vitro established and micropropagated. Micrografts were successfully achieved from bitter almond homografts and Canhota (Portuguese traditional variety) x bitter almond rootstocks. IAA quantification performed through Ehrlich reaction, showed a scion content of 1.292±0.448 μg IAA/ mg FW (Canhota) and 5.505±1.179 μg IAA/ mg FW (bitter almond) before micrografting, and the potential influence of these levels on micrograft success. Through IAA immunolocalization a possible accumulation at the graft union in the scion part was observed. The results obtained here are a step forward to the understanding of how scion and rootstock communicate in different almond tree micrograft combinations and how their communication is associated with graft success.