Estimation of chilling and heat requirements of peach and nectarine cultivars grown under different pedoclimatic conditions

Climate change is already depicted as an increase in winter temperatures resulting in lower chilling accumulation that is required for proper flowering and subsequent fruit set in temperate fruit species. Since temperature requirements are cultivar-specific, the knowledge of these requirements may be valuable for predicting the adaptability of each cultivar to particular areas. The most widely used method for estimating chilling requirements is the Tabuenca test. However, little is known on the stability of results obtained from the above methodology in different years or pedoclimatic conditions. To this aim, experiments were carried out in Lleida (Spain) and Naoussa (Greece) on 14 different peach and nectarine cultivars, representing a wide range of pomological and phenological characteristics, belonging to the EUFRIN testing trial network. Chilling accumulation was similar in both locations, but the most efficient chilling period was earlier in winter in Lleida, resulting to a mean of a 2-day earlier end of dormancy (15 January vs 17 January). Following endodormancy, heat accumulation was much higher in Naoussa resulting in a 12-day earlier beginning of bloom, suggesting that blooming time was more regulated by heat rather than cold accumulation in both locations. Chill requirements of the studied cultivars were estimated using four models; low coefficient of variation (CV%) was observed using the Dynamic, Utah and Positive Utah Models. Instead, high CV% was found with the Chilling Hours model and no significant differences among cultivars, indicating for a low suitability in the studied regions. Chilling requirements ranged from 48.3 to 68.7 Chilling Portions (CP); in the lowest range were 'Carla', 'Patty' and 'Big Top' (48.3, 51.0 and 55.8 CP, respectively) whereas 'Catherina' and 'O'Henry' (64.0 and 68.7 CP, respectively) had the highest chilling requirements. No differences in heat requirements among the examined cultivars was monitored. There was no effect of location on chilling and heating requirements of the studied cultivars, apart from the Positive Utah and Chilling Hours models; to this aim more studies under more contrasting chilling regimes are needed to further elucidate the effect of pedoclimatic conditions for a given cultivar.

Automated summary

Climate change affects chilling accumulation and has an impact on flowering and fruit set in temperate fruit species. Understanding temperature requirements is important for predicting adaptability. The Tabuenca test is commonly used to estimate chilling requirements, but its stability is uncertain. Heat accumulation appears to play a more significant role than cold accumulation in regulating blooming time.