Effect of climatic conditions on the overcoming of dormancy in apricot flower buds in two Mediterranean areas: Murcia (Spain) and Tuscany (Italy)

For temperate-zone fruit species such as apricot, when winter cold requirements are not adequately satisfied, negative repercussions on productivity occur. The aim of this research was to study the effect of, mainly temperature on the overcoming of dormancy in different apricot cultivars growing in two areas (Italy, Tuscany: lat. 43°02′N, long. 10°36′E; Spain, Murcia: lat. 38°16′N, long. 1°16′W) representative of the Mediterranean climate. Trials were conducted for two consecutive years on the same genotypes: ‘Currot’, ‘San Castrese’, ‘Goldrich’, ‘Stark Early Orange’ and ‘Orange Red’. These genotypes cover the range of chilling requirements (CR) in the apricot species in these Mediterranean areas. The CR (measured by chill units, CU and portions) for breaking of dormancy, heat requirements, flowering date and flowering and fruit-set percentages were measured. Temperatures were recorded and transformed into the corresponding CU and portions by the Utah Model and the Dynamic model, respectively. The winter climatic conditions determined a dissimilar chill unit accumulation in Tuscany (Italy) and Murcia (Spain) as well as an important effect of the year in both areas. While all cultivars with the exception of Stark Early Orange overcame dormancy, significant differences regarding the CR of cultivars for two different years and growing in two environments were observed, depending also on the cultivar. The results showed that both the Utah Model and Dynamic Model were not completely accurate with regard to establishing the CR for dormancy release under a Mediterranean climate. Temperature should be analysed together with other climatic factors in order to improve the CR assessment.