Effect of biotic and abiotic factors on the incidence of fruit scars in Italian orange orchards

Citrus fruit rind scars are corky tissue formations, the structure, shape and distribution of which may be very variable on the fruit surface. Such phenomena have been increasingly recorded during the last few years on lemon and orange fruits, as confirmed by surveys carried out in several Italian packing houses. They are referred to fruit scars induced by various biotic factors such as thrips feeding and physical damage, mainly caused by brunch rubbing due to wind or spraying equipments. In 2011, a field survey was conducted in a Sicilian organic orange orchard, to evaluate possible correlation between thrips infestation, brunch rubbing and fruit scars. Two plots were evaluated; one planted with the variety ‘Navelina’ and the other with ‘Tarocco Scirè’. No insecticides were applied during the observation period. Thrips infestation was monitored weekly from the flowering to fruit-set, and type, incidence and severity of fruit scars were assessed by field direct observations at fruit-set and harvest. In addition, a survey was carried out in 7 packing houses located in the same production area to assess the rate of downgrading due to fruit scars. Although very few flowers and young fruits were found infested by thrips (mainly Pezothrips kellyanus and Frankliniella occidentalis), a high incidence of damaged fruits (up to 40%) was observed in both varieties, with scars apparently due to mechanical damage. The same trend, both in terms of type and incidence, was observed during the packing houses survey with an average of 35% of scared fruits (min 20-max 50%). The results showed that few scars are attributable to thrips infestation, while physical factors, notably wind and spraying equipment, play the key role. This finding also stresses the urgent need to carefully discriminate the origin of fruit scars in order to avoid unnecessary insecticide applications in citrus.