• Energy Research

AbstractProfessional and scientific networks built around the production of sweet cherry (Prunus avium L.) led to the collection of phenology data for a wide range of cultivars grown in experimental sites characterized by highly contrasted climatic conditions. We present a dataset of flowering and maturity dates, recorded each year for one tree when available, or the average of several trees for each cultivar, over a period of 37 years (1978–2015). Such a dataset is extremely valuable for characterizing the phenological response to climate change, and the plasticity of the different cultivars’ behaviour under different environmental conditions. In addition, this dataset will support the development of predictive models for sweet cherry phenology exploitable at the continental scale, and will help anticipate breeding strategies in order to maintain and improve sweet cherry production in Europe.

In the current context of global warming, an analysis is required of spatially-extensive and long-term blooming data in fruit trees to make up for insufficient information on regional-scale blooming changes and determinisms that are key to the phenological adaptation of these species. We therefore analysed blooming dates over long periods at climate-contrasted sites in Western Europe, focusing mainly on the Golden Delicious apple that is grown worldwide. On average, blooming advances were more pronounced in northern continental (10 days) than in western oceanic (6-7 days) regions, while the shortest advance was found on the Mediterranean coastline. Temporal trends toward blooming phase shortenings were also observed in continental regions. These regional differences in temporal variability across Western Europe resulted in a decrease in spatial variability, i.e. shorter time intervals between blooming dates in contrasted regions (8-10-day decrease for full bloom between Mediterranean and continental regions). Fitted sequential models were used to reproduce phenological changes. Marked trends toward shorter simulated durations of forcing period (bud growth from dormancy release to blooming) and high positive correlations between these durations and observed blooming dates support the notion that blooming advances and shortenings are mainly due to faster satisfaction of the heating requirement. However, trends toward later dormancy releases were also noted in oceanic and Mediterranean regions. This could tend toward blooming delays and explain the shorter advances in these regions despite similar or greater warming. The regional differences in simulated chilling and forcing periods were consistent with the regional differences in temperature increases.

Peach and apricot trees usually set more fruit than they can adequately support. Crop load adjustment through fruit thinning is a routine practice adopted by fruit growers to obtain a marketable product. However, hand thinning is an expensive, labor-intense operation. The interest in the mechanization of thinning has increased in the last decades. A new machine, consisting of a tractor-mounted rotor equipped with elastic rods radially inserted on a central axis, has been recently developed to thin both flowers and green fruits in stone fruit crops. In order to test its effectiveness and optimize the operative conditions, trials were carried out in 2016 in two apricot and two peach commercial orchards located in the northeast Italy. Tests were carried out on narrow-canopied orchards, during blooming time, and on green fruit, assessing the flower and fruit removal percentage and the labor saving as compared with the standard fruit hand-thinning practice. In apricot, the machine removed 20.8% of flowers and 43.6% of fruit, allowing 48% time saving in the follow-up fruit manual thinning as compared with the control (hand-thinning only). In peach, mechanical thinning at blooming time removed 63% of flowers, allowing 42.4% time saving in the follow-up fruit manual thinning as compared with the control, whereas mechanical thinning of fruit at the beginning of pit hardening stage removed less than 10%. The development of a mechanical thinning practice, complemented by a manual finishing, could represent a valuable near-term solution to reduce thinning labor time.