Chilling and heat requirements in the flower and vegetative buds of some local almond cultivars

Determination of chilling and heat requirements is respected in the selection of the suitable cultivars for producers to avoid damages caused by an inadequate winter chilling in a certain area. It also play an important role within a breeding program, when selecting parents to get late or early flowering cultivars. The present study aimed to estimate the chilling and heat requirements of breaking bud dormancy for flowering and vegetative growth in three Iranian almond cultivars in an orchard located in the suburbs of Garmdarreh (32.45 & DEG;N; 50.91 & DEG;E; altitude 1960 m). The three almond cultivars had different flowering times, i.e. early: Modified Letter Turned CommaMoheb & apos;, medium: Modified Letter Turned CommaMamaie & apos; and late: Modified Letter Turned CommaRabi & apos;. To provide adequate chilling, fourteen-year-old trees were exposed to low temperature treatments (4 & PLUSMN; 1 & DEG;C) to simulate 0-1500 h of chilling at 250 h intervals. The cultivars varied in their chilling and heat requirements in terms of chilling hours and growing degree hours, GDH, to achieve bud break for flowering, i.e. 'Moheb' (250 h and 2132 GDH), 'Mamaie' (500 h and 2460 GDH) and 'Rabi' (500 h and 2624 GDH). To achieve bud break for leaf growth, the late-leafing cultivar ('Rabi') required 750 chilling hours and a heat requirement of 3608 GDH. The earlier-leafing cultivars ('Moheb' and 'Mamaie') had lower heat requirements for leaf unfolding. Although 'Rabi' and 'Mamaie' had similar chilling requirements of 500 h, 'Rabi' required almost a week (168 h) of warm weather after chilling to achieve bud break. This implies that spring frost is rarely a problem for 'Rabi' in Iran. 'Moheb' was not suitable because of its low chilling and heat requirements, hence its inability to escape early spring frosts and late winter cold.