Estimation of chilling and heat requirements for flowering in almond

Abstract

Assessment of chilling requirements for breaking dormancy (CR) and heat requirements for flowering (HR) in fruit trees is important for selecting cultivars suitable for the climatic conditions of the site. The objective of this study was to estimate CR and HR in six almond cultivars grown in the Belgrade region. The study was conducted during a three-year period. The CR was quantified using the Utah chill unit model (CU). The date of completion of CR was determined according to the weight increase and phenological transition of forced flower buds in controlled conditions. The HR was determined as growing degree hours (GDH) accumulated from the breaking of dormancy to the beginning of flowering using a base temperature of 4°C. The CR ranged from 690 CU in 'Exinograd' to 1285 CU in 'Mari de Stepa'. The HR varied between 3838 GDH in 'Ferragnes' and 4539 GDH in 'Mari de Stepa'. The earlier-flowering cultivars were those with the lowest CR. The latest flowering cultivar 'Mari de Stepa' (April 11) finished dormancy on average 51 days after the earliest flowering cultivar 'Exinograd' (March 29).