Determination of Chilling and Heat Requirements of Pistachio (Pistacia vera L.) Cultivars

Determination of chilling and heat requirements of pistachio (Pistacia vera L.) cultivars is important for satisfactory growth and development, particularly when large-scale commercial production is desired. This experiment was conducted to determine chilling requirement inducing vegetative and flower buds of Kalle-Ghuchi, Owhadi, Ahmad-Ahgaei, and Akbari pistachio. Shoots with enough vegetative and flower buds were taken from pistachio trees during autumn 2007 and 2008 when temperature reached to 15°C. Cuttings with flower buds were kept under (5±1)°C for 0, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, and 1300 h, respectively, and cuttings with vegetative buds were kept at 51°C until 1 500 h. The results indicated that pistachio cultivars requite chilling time between 750–1 400 h and heat requirements between 8 852-15 420 growing degree hours (GDH). Consequently, Kalle-Ghuchi had the lowest chilling (750–950 h), and heat (8852–9768 GDH) requirements, Ahmad-Aghaei and Owhadi had intermediate (1000–1250 h, 10656–13320 GDH) and Akbari had the highest chilling (1200–1400 h) and heat (11863–15420 GDH) requirement.