Plant bioregulators: do we still need them?

Plant growth regulators (PGRs) are substances able to interfere with the plant’s hormone system controlling several physiological processes in trees. Since the discovery of plant hormones, the use of PGRs have offered the possibility to control different production steps, from the nursery to open-field. Even in a period characterized by a certain reticence towards agrochemicals, the research on the use of PGRs is still ongoing and the main chemical industries have introduced new molecules on the market. Traditional PGRs are finding new interesting uses and the new ones can represent a solution to the increasingly pressing demands coming from growers. In addition, these compounds might represent an additional tool to help solving problems linked to climate changes that afflict various physiological processes of plants (fulfillment of the chilling requirements, fruit skin colour, fruit load) managing to balance canopy growth and fruiting. In this contribution some examples on the use of PGRs are reported, focusing in particular on the latest formulations that have appeared on the market in recent years. It has to be kept in mind that the PGRs, although being an important tool, must be considered just an option among the portfolio available to the grower for improving quantity and quality of fruit production and that a proper use of PGRs requires a deep understanding of the physiological mechanism of the process to obtain the desired effects avoiding the collateral side-effects