Effect of fruit thinning on fruit quality and alternate bearing of ‘Setubalense’ mandarin (Citrus deliciosa)

Citriculture plays a major role in agriculture worldwide, especially in the Mediterranean region. However, there are limitations in citrus production. Alternate bearing can be a big problem when it is very intense. Trees produce a heavy yield one year (“on” year) and light ones the next (“off” year). During the “on” year, trees produce many small-sized fruits, while in the “off” year, they produce very few, larger fruits. The small size of the fruits is a limitation, as they are less well accepted in the market. The ‘Setubalense’ cultivar, a traditional Portuguese Mediterranean mandarin (Citrus deliciosa), is recognized for its excellent organoleptic characteristics. Despite this, the issues of alternate bearing and small fruit size are leading to the loss of this cultivar. Fruit thinning is a cultural practice involving the removal of some fruits, while leaving others. This practice can be used to manage alternate bearing and to improve fruit size. However, its impact on the plant is not well understood, whether it affects the plant as a whole or at a more localized level, such as within individual branches. To address this, two experiments were installed in August 2019. In the first experiment thinning involved removing 50% of the fruits from the entire tree. In this experiment, the fruit size and fruit quality were higher in the trees where fruit thinning was performed. In the second experiment, thinning was applied to selected branches, also removing 50% of the fruits. In this case, no significant differences were observed, neither in fruit size nor in fruit quality. Furthermore, fruit thinning did not reduce alternate bearing in either experiment.