153 Journal of Nuts Journal homepage: ijnrs.damghaniau.ac.ir Journal of Nuts 12(2) (2021) 153-164 Determination of Cold Hardiness of Pistachio (Pistacia vera L.) Cultivars Flower Buds during Rest Season Zahra Pakkish *1 , Hadi Asghari 2 1 Associate Professor, Department of Horticultural Sciences, Faculty of Agriculture, Shahid Bahonar University of Kerman, Kerman, Iran 2 Researcher of Horticultural Science, Agricultural Research Center and Natural Resources, Kerman, Iran A R T I C L E I N F O A B S T R A C T Keywords: Cold hardiness; Dormancy; Low temperatures, Pistachio trees 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 о C, held for 24h at each temperature. The critical temperature for survival among the 4 cultivars was -15 о C and more than 70% of the buds of all cultivars were killed once they were subjected to -30 о 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. Introduction Pistachio tree (Pistacia vera L.) originates from Central Asia. It is an important commercial nut tree in Iran and has adapted to the native climate (Shamshiri and Hasani, 2015; Sharifkhah et al., 2010). Iran ranks No.1 in pistachio production and harvest area in the world while few research activities concerning the morphology and physiology of the pistachio trees have been carried out in this country. Therefore, the knowledge of the hardiness responses of pistachio trees is essential for economic production. Freeze injury to pistachio trees has severely decreased yield in many commercial orchards during the recent years in Iran. However, susceptibility to freeze damage appears to vary considerably between cultivars and should therefore, be amenable to breeding efforts (Ameglio et al., 2004, Arora et al., 1992, Ashworth, 1990, Aslamarz et al., 2010, Fuller and Wisniewski 1998, Lindsrom and Dirr 1991, Thomashow 1999). Low winter temperatures are a major limiting factor in fruit production in the world, a major challenge is that adaptation to climate change is not a one-size fits all phenomenon; adaptation strategies and farmer responses will vary across regions (Ameglio 1990, Ashworth 1996, Aslamarz et al., 2009, Flinn and Ashworth 1998). Temperature is a primary factor affecting the rate of plant development and economic losses can occur due to very low temperatures during dormancy or due to untimely freezing temperatures before acclimation in the fall or after de-acclimation in the spring, the flower bud remains dormant for several months in pistachio (Bordelon et al., 1997, Morin et al., 2007). Due to the importance of cold hardiness in fruit production, this characteristic is often a selection criterion in cultivation fruit trees (Beck et al., 2007, Ishikawa and Arata 1997). Low temperatures decrease biosynthetic activity of plants, inhibit the normal function of physiological processes and may * Corresponding author: Email address: zahrapakkish@uk.ac.ir Received: 8 December 2020; Received in revised form:10 February 2021; Accepted: 1 June 2021 DOI: 10.22034/jon.2021.1917292.1098 153