Apricot bud chilling and heat requirements in two different climatic areas: Murcia and the Tuscan Maremma

Trials were set up in two sharply differing climatic environments (Murcia and Tuscan Maremma), using some cultivars common to both areas. Apricot twigs were collected periodically during three consecutive winters. Sample flower buds were weighed before and after a one-week period of forcing in a climatized cell, to determine the time of endodormancy breaking. Chilling and heat requirements were thus determined experimentally in terms of CU and GDH. Comparative analysis of results obtained on different cultivars revealed considerable variation among years and environments, affecting both the amount of CU required for dormancy breaking and amount of GDH needed to reach the beginning of the flowering stage. There is an inverse regression between these values: more heat could partially compensate the low amount of chilling. Variability among years was more marked in Murcia than in Tuscan Maremma. In the latter environment, chilling requirements were fairly constant over the years, although noteworthy variation in yearly heat requirements was observed. Forecasting the flowering date of the various cultivars on the basis of the sum of CU and GDH therefore appears unreliable. The expected date may also be influenced by the presence of eco-dormancy, a phenomenon not previously considered in the phenoclimatic model utilized. Overall, it did not prove possible to establish a correlation between chilling requirements and abundance of flowering.