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

Abstract 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 different climatic conditions, 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. 38º16’N, long. 1º16’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 chilling requirements (measured by chill units, CU) for breaking of dormancy, heat requirements, flowering date and flowering and fruit set percentages were estimated. Temperatures were recorded and transformed into the corresponding CU by the Utah Model. 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 (SEO) overcame dormancy, significant differences regarding the chilling requirements (CR) of cultivars growing in the different environmental conditions were observed. The variability of results shows that 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.