Top Netting Reduces Citrus Fruit Cracking

Fruit cracking is a fruit peel physiological disorder. In citrus, it typically results in fruit splitting and abscission. Cracking is related to plant water factors and the irrigation regime; heavy or non-regular irrigation is correlated with elevated cracking incidence. In addition, cracking is more common in larger fruit than in smaller ones. Some cultivars are more prone to cracking, suggesting that the phenomenon has a genetic background. However, it has become evident that climatic conditions also affect fruit cracking. As a result, some years are characterized by heavy cracking incidence, and this may be associated with yearly climate variations. Top netting is a useful tool to mitigate microclimates, and it can potentially reduce cracking intensity. We conducted a five-year experiment in a commercial 'Valencia' orange orchard, using three different photoselective nets and three distinct irrigation regimes: the recommended level (100%), and two reduced regimes (80% and 60%). Out of the five experimental years, cracking occurred in three years with various intensities. As expected, reduced irrigation in control trees resulted in decreased cracking intensity, and there was a positive relationship between the fraction of cracking and larger fruit size. In netted trees, the cracking intensity was reduced regardless of net color, irrigation regime or fruit size. During the summer, canopy temperature was reduced under the nets, and relative humidity increased. The possible involvement of climatic parameters, modified under the nets, in altering cracking intensity is discussed. Results of this experiment demonstrate the potential of top-netting technology to mitigate cracking intensity in citrus.