Exposure to the Endophytic Fungi Regulates the Anthocyanin Profiles in the Post-Veraison Grape Berries of ‘Cabernet Sauvignon’

The potential of endophytes to initiate changes in host secondary metabolism is expected to be applied to improve the biochemical qualities of the crop. Our previous study revealed the significant impacts of fungal endophytes on the biochemical properties and the anthocyanin profiles in grape berries of the local cultivar ‘Rose Honey’ (RH). To validate the effects, our present work further assessed the impacts of the same fungal endophytes on grape berries of the worldwide planted grapevine cultivar ‘Cabernet Sauvignon’ (CS). Consistent with the results of RH, exposure to most of the used endophytic fungi shaped the biochemical traits and anthocyanidin profile of the CS grape berries. Among the detected biochemical traits, the phenylalanine ammonia-lyase (PAL) activity in berries had the strongest response to endophytic fungal exposure, and the fungal strains RH32, RH36, and MDR1 had the greatest biochemical impacts on the grape berries. Interestingly, the most anthocyanidin species were detected in the two grape berry varieties when exposed to fungal strains MDR36 and RH34. In both varieties, the total anthocyanin concentrations were quantitatively promoted by strains RH36, RH44, MDR1, and MDR36, but suppressed by strain RH7. Malvidin derivatives and delphinidin derivatives accounted for the majority of the relative abundance of the total detected anthocyanins in CS berries. The acylation degree of anthocyanins in grape berries was also significantly promoted by exposure to fungal endophytes. In CS grape berries, a seldom-distributed anthocyanidin, pelargonidin-3-O-glucoside, as well as the diglucoside anthocyanidin were detected when exposed to fungal strains as RH32, RH34, RH36, MDR1, MDR4, and MDR36. Overall, the endophytic fungal strains MDR36, RH36, and RH34 have the ability to promote metabolite profiles in both grape varieties. This work confirms the possibility of using certain endophytic fungal strains as a strategy for shaping grape pigmentation in vinification at the post-veraison or post-harvest stages