Graft compatibility of Vitis spp.: the role of phenolic acids and flavanols

•Relationship between phenolic compounds and Vitis graft compatibility was studied.•Combinations of Syrah cultivar with rootstocks 110R and SO4 were analysed.•Gallic, ferulic and sinapic acids are closely related to the level of compatibility of grafting combinations.•Significant differences in their levels above and below graft union are response to grafting.•Rooting seems to be the most critical stage of grafting cycle.