Chilling and heat requirements of ‘Tardona’, the latest flowering almond cultivar released in the world

Abstract

Flowering time is one of the most important traits for almond (Prunus dulcis) breeding and it is determined by the specific chilling and heat requirements of each genotype. After being exposed to periods of low (chill units, CU) and high temperatures (growing degree hours, GDH), the tree is able to break its dormancy, flower and sprout. Chill requirements are calculated according to Richardson and Dynamic models. Heat requirements are estimated as the mean hourly temperatures minus 4.5°C, between the breaking of dormancy and the full flowering time (when 50% of flowers are open, F50). For a suitable flowering, vegetative growth, and fruit set, chilling requirements have to be fully satisfied. In the cold areas, where the new almond orchards are being stablished, late-flowering is an obligatory trait to avoid late frosts. 'Tardona', bred in CEBAS-CSIC, is the latest flowering almond cultivar released in the world up to now. In this work, chilling requirements for breaking dormancy and heat requirements for flowering of 'Tardona' were calculated by two methods for two seasons.