Impact of Chill and Heat Exposures under Diverse Climatic Conditions on Peach and Nectarine Flowering Phenology

Abstract

The present study aims to generalize cultivar-specific tree phenology responses to winter and spring temperatures and assess the effectiveness of the Tabuenca test and various chill and heat accumulation models in predicting bloom dates for a wide range of climatic conditions and years. To this end, we estimated the dates of rest completion and blooming and correlated them with observed bloom dates for 14 peach and nectarine cultivars that were evaluated in 11 locations across Europe (Greece, France, Italy, Romania and Spain), within the EUFRIN cultivar testing trial network. Chill accumulation varied considerably among the studied sites, ranging from 45 Chill Portions (CP) in Murcia-Torre Pacheco (Spain) to 97-98 CP in Cuneo (Italy) and Bucharest (Romania). Rest completion occurred latest or was not achieved at all for some cultivars in the southern sites in Murcia. Dormancy release happened earliest in Bucharest and Cuneo, sites where heat accumulation had a strong influence on the regulation of bloom time. Blooming occurred earliest in the moderately cold regions of Lleida (Spain) and Bellegarde (France), and 7-11 days later in the warmer locations of Rome (Italy) and Naoussa (Greece), suggesting that bloom timing is strongly influenced by delayed rest completion in these locations. The Dynamic Model resulted in both more homogeneous chill accumulation across years and better predictions of bloom dates, compared with the Utah, Positive Utah and Chilling Hours models. Prediction of bloom dates was less successful for low-chill cultivars than for medium- and high-chill cultivars. Further climatic and experimental data are needed to make estimates of the climatic needs of peach cultivars more robust and to generate reliable advice for enhancing the resilience of peach production under varying and changing climatic conditions.

Keywords: Prunus persica; chilling requirement; heat requirement; resilience.

Figure 1

Heat-map presenting monthly mean temperature (°C) during October–March 2019–2022 in 11 European sites, presented from the coolest to the warmest. Mean values of monthly mean temperatures are presented for the above periods in each site and month. X = no data. YE = Yéchar; TP = Torre Pacheco.

Figure 2

Heat-maps presenting the sum of chill accumulation during 15-d periods (from 1 October to 29 February) and yearly sums (2019–2022) and calculated with the (a) Dynamic (Chill Portions), (b) Utah (Chill Units), (c) Positive Utah (Positive Chill Units) and (d) Chill Hours models. X = no data. YE = Yéchar; TP = Torre Pacheco.

Figure 3

Heat-map presenting heat accumulation (in growing degree hours (GDH) (X10¹)) accumulated during 15-day periods from 1 October until 29 March in 11 European sites in the 2019–2022 three-year period. The sum of GDH during February–March is also presented for each studied period and year. X = no data. YE = Yéchar; TP = Torre Pacheco.

Figure 4

Heat-map showing Julian days of dormancy release, estimated as the day that chill was satisfied, for 14 peach and nectarine cultivars grown in 11 European sites, during (a) 2020, (b) 2021, (c) 2022, and (d) mean values. X = no data. Empty cells indicate that dormancy release was not achieved. YE = Yéchar; TP = Torre Pacheco. Negative values indicate days in the previous year. Means with different letters indicate significant differences among sites and cultivars, using the Tukey multiple range test.

Figure 5

Heat-map showing Julian days of beginning of bloom in 7 cultivars located in 9 sites. Mean values for 2021 and 2022 are shown. X = no data. YE = Yéchar. Means with different letters indicate significant differences among sites and cultivars, using the Tukey multiple range test.

Figure 6

(a,b) Root mean square error (RMSE), and (c,d) ratio of performance to interquartile distance (RPIQ), for the observed versus estimated full bloom dates for (b,d) 14 peach and nectarine cultivars, and (a,c) at 11 European sites, calculated using four models. Sites are presented from those having the highest to the lowest chill accumulation, and cultivars from having the lowest to the highest chill requirements. Chill requirements are estimated using the Dynamic Model.