Effect of plant growth regulators for enhancing fruit quality in Italian citrus industry

Improving fruit quality for fresh consumption in citrus is an increasingly important challenge. The obtainment of adequate fruit size and of a regular production over years represent important aspects that can mostly be regulated by agronomical techniques. As known, there are several strategies useful to increase fruit size, such as manual and chemical thinning or hormone treatments to stimulate cell division. Fruit thinning can also positively influence yield reducing alternate bearing. Different plant growth regulators (PGR) are currently used in citrus industry worldwide but, on local and novel varieties in citrus growing countries, protocols need to be set up. In the last years a number of trials on the most important blood orange and mandarin-like varieties cultivated in Sicily have been carried out. The study reports the main results on PGR tested on different varieties. In particular, auxins applied during June-drop were effective in fruit thinning and in fruit size increasing, though alternate bearing behavior remained unaffected. Some auxins also increased fruit size in some blood oranges when applied during fruit development, and were also effective in reducing preharvest fruit drop. The overall results of these trials are presented and evaluated in this paper with special emphasis on crucial aspects for their introduction in the citrus industry.