The cost of flowering in olive (Olea europaea L.)

A five-year study was carried out in central Italy (Region of Umbria) to quantify the biomass investment in flowering in relation to the total biomass investment for fruit production. In all the years the inflorescences started growing in mid April and showed intense growth, especially in the last 20 days before the beginning of flowering. The inflorescence fresh and dry weights, recorded just before flowering (at the "white stage" of development), ranged between 155-349 mg and 53-96 mg, respectively, corresponding to a biomass expressed in glucose equivalents of 66-120 mg. After full bloom, inflorescence weight decreased remarkably due to flower drop. At the whole-tree level, fresh weight, dry weight and glucose equivalents of inflorescences (just before the beginning of flowering) and fruits (at harvest) ranged, respectively, from 0.8 to 4.2, 0.3-1.2 and 0.4-1.5 kg tree(-1) and 7.4-15.5, 3.5-9.0 and 7.7-20.1 kg tree(-1). Inflorescence mass was 8-39% of the fruit mass when expressed on a fresh weight basis per tree, 5-24% when expressed on dry weight and 3-16% when expressed as glucose equivalents. The results showed a relatively important cost of flowering, especially in some years and considering that most of the biomass was accumulated in a short time (about 20 days). In fact, the daily inflorescence biomass accumulation during the last 20 days before bloom, expressed as glucose equivalents, ranged from 14 to 126 g tree(-1) day(-1), showing that in years of high production of flowers, when the highest rates of biomass accumulation were recoded, it reaches values similar to the average daily biomass accumulation in fruits (expressed in glucose equivalents), which was 47-122 g tree(-1) day(-1). Given the significant effort in flower production in olive, the consequences and the function of the redundant flowering (i.e. fruit set is very low in olive) is discussed.