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

The role of phenolic compounds in graft compatibility has been widely studied in various fruit species. However, little information is available for Vitis spp. This work aims at investigating the differences in phenolic acid and flavanol content in various scion/rootstock systems and understanding if they can be used as chemical markers of graft compatibility, using combinations of the Syrah cultivar (clones FR 470 and FR 383) with two rootstocks (110R and SO4). For this purpose, extracts of grafting tissues collected above graft union, at the graft union and below graft union from each combination at crucial stages of the grafting cycle (callusing, rooting and end of cycle) were prepared and analysed by HPLC. The results obtained revealed that the contents in gallic, ferulic and sinapic acids are closely related to the level of compatibility of the studied grafting combinations. The less compatible combinations (Syrah383/110R and Syrah383/SO4) exhibit higher content of gallic acid and lower contents of ferulic and sinapic acids than the more compatible ones (Syrah470/110R and Syrah470/SO4). In addition, these phenolic acids accumulated in the graft union and in the adjacent sections as a response to grafting. A significant difference in their levels was detected between the above and below graft union sections, especially at the rooting stage. Therefore, they can be seen as chemical markers to be used in an early detection of graft compatibility, preferably performed at the rooting stage and targeting the sections above and below the graft union.