Growth and development of fruits of olive 'Frantoio' under irrigated and rainfed conditions

A field experiment was performed in Tuscany, Italy, whereby fruit growth and development of irrigated olive trees (Olea europaea L. ‘Frantoio’) were compared, at two stages of fruit development, with those of trees cultivated under rainfed conditions. The fresh weight of fruits from irrigated trees was significantly higher than that from rainfed trees at 21 weeks after full bloom (AFB), whereas there were no differences at 8 weeks AFB or in fruit dry weight at both dates. Mesocarp transverse equatorial areas were 15.6 and 13.5% greater for the irrigated treatment than rainfed cultivated trees at 8 and 21 weeks AFB, respectively. Endocarp transverse area did not increase between 8 and 21 weeks AFB, indicating that endocarp expansion had occurred completely by 8 weeks AFB. The endocarp transverse area of irrigated trees was greater than that of unirrigated trees. For both treatments, mesocarp transverse area increased about 2.5-fold from 8 to 21 weeks AFB. Growth of the mesocarp between sampling dates was mainly due to a more than two-fold increase in mesocarp cell size for both treatments, whereas cell number increased only slightly over the same period. Irrigation appeared to increase mesocarp cell size rather than mesocarp cell number on both sampling dates. There were no differences in mesocarp oil content between irrigated and rainfed trees either at 8 or at 21 weeks AFB.