Field spatial pattern of seedy fruit and techniques to improve yield on ‘Afourer’ mandarin

Abstract

Cross-pollination increases the number of seedy fruit in a wide range of Citrus cultivars including self-incompatible cultivars such as ‘Nadorcott' mandarin, thereby diminishing the commercial value of the crop. Isolated block planting and whole tree net-covering are some of the techniques applied to increase seedlessness of cross-pollinated varieties. However, in net-covered trees a reduction in yield has been reported. The purpose of this work was to study the spatial distribution of seedy fruit at different distances from other pollen sources, and to evaluate the effect of different fruit set promoting techniques applied to covered trees under commercial field conditions. To this aim, four experiments were carried out in a commercial orchard of ‘Nadorcott' mandarin to assess: a) the spatial distribution of seed number per fruit and seedy fruit under open-pollinated conditions; b) the effect of girdling and gibberellic acid (GA3) application on fruit set and seedless fruit in net-covered trees; and c) seedless fruit number in open pollinated trees treated with GA3 and consecutive copper sulphate (CuSO4) sprays. A gradual reduction in the percentage of seedy fruit from the pollen source up to 140m away from where the seedless fruit presented a spatially randomized pattern. Net-covered trees reduced the number of seedy fruit and the number of seeds per fruit, whereas the number of fruits was reduced by 66%. Under nets, single GA3 spray, but not girdling, impaired fruitlet drop. Six consecutive 25mg per liter or 50mg per liter sprays of CuSO4 reduced the number of fruit per tree, the 50mg per liter dose increased fruit seedlesness. Single GA3 25mg per liter sprays or combined with CuSO4 reduced the number of seedy fruit with the reduction in fruit per tree.