Determination of Cold Hardiness of Pistachio (Pistacia vera L.) Cultivars Flower Buds during Rest Season

Frost injury is a very widespread phenomenon occurring in both deciduous and ever-green trees such as pistachio. The cold hardiness levels of four cultivars of pistachio (Pistacia vera L.), ‘Kalle- Ghuchi’, ‘Owhadi’, ‘Ahmad-Aghaei’ and ‘Akbari’ were determined. Samples were collected from November 2007 to March 2008 and from November 2008 to March 2009, with three week intervals during dormant season. Then, single- bud cutting sections were placed in incubator and subjected to temperature, +5 (control), -10, -15, -20, -25 and -30˚C, held for 24h at each temperature. The critical temperature for survival among the 4 cultivars was -15˚C and more than 70% of the buds of all cultivars were killed once they were subjected to -30˚C. All cultivars achieved a maximum cold hardiness in December and January. These four cultivars were classified as hardy (‘Akbari’), semi-hardy (‘Owhadi’ and ‘Ahmad-Aghaei’) and sensitive (‘Kalle-Ghuchi’). The tested pistachio cultivars exhibited higher cold hardiness levels in ‘OFF’ trees, rather than ‘ON’ trees.