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The frost hardiness of fi ve apricot (Prunus armeniaca L.) cultivars used for drying and/or the fresh market was investigated under controlled conditions and in the orchard. The hardiness of fl ower buds at three different development stages, such as fi rst white, fi rst bloom, and full bloom, was tested at -4 °C for 1 hour and 3 hours in the laboratory. The fl ower buds of 'Kabaasi', 'Sekerpare', and 'Alyanak' were hardier. The fi eld observations obtained from the apricot orchard where the late frost occurred at night on 3 to 4 Apr. 2004 supported this result, and the temperatures at frost date varied from -2 to -9 °C. Low temperatures during and after bud- break may limit the distribution of deciduous fruit trees and may also seriously impair fruit production caused by freezing injuries in areas where the particular crop is already well established (Rodrigo, 2000). The most signifi cant damages occur in buds, fl owers, developing fruits and also shoots (Smeeton, 1964). Furthermore, year-to-year variations in crop production traditionally related to weather conditions in the spring also cause major economic losses. While the main causes determining cold hardiness are not certain (Ashworth, 1986; Guy, 1990; Thomashow, 1998), some factors such as genotype, devel- opmental stage, the formation of ice, moisture content, nutritive status of the pistil and even environmental factors have been mentioned in the resistance of fl ower buds to spring frosts. In addition, destructive critical temperatures vary on not only the phenological stage, but also vary among species, cultivars, orchards (Proebsting and Mills, 1978a), and even within the trees (Westwood, 1993). Apricot (Prunus armeniaca L.), is one of the most important stone fruits grown in the world after peach and plum. The world apricot production is about 2,7 million tons (FAO, 2004), and Turkey is one of the lead- ing producers especially in the drying market. Since Turkey supports about 80% (71,900 t) of the world dried apricot export (91,011 t) (FAO, 2003), there are a lot of cultivars hav- ing high soluble solids content suitable for drying in Turkey. The most known cultivar is 'Hacihaliloglu' (Layne et al., 1996). The world dried apricot production and trade have been seriously affected and have dropped 2-fold in some year because of late spring frosts. It will be very benefi cial to de- termine frost hardiness of cultivars especially suitable for drying in Turkey. As it is well known, apricot is susceptible to spring frost because of its early bloom period in the spring and structure of its fl owers. So, spring frosts are the most important environmental factor limiting apricot yield in Turkey. Information about spring frost hardiness during the bloom period of apricot cultivars is limited. Some data on low temperature hardi- ness of apricot fruit buds has been focused on recently bred cultivars, but most of them are mainly on the critical winter temperatures (Layne, 1978, 1984, 1991; Mehlenbacher et al., 1987). Critical winter temperatures were reported as -3.9 and -2.2 °C at the fi rst white and full bloom development stages of fl ower buds, respectively, for the spring frosts (Rogers and Swift, 1970). This paper presents the spring frost hardiness of fl ower buds at three different developmental stages for fi ve apricot cultivars used for drying and/or fresh eating. Plant Material The spring frost hardiness was deter- mined in the fl ower buds of 'Hacihaliloglu', 'Cataloglu', suitable for drying, 'Sekerpare', 'Alyanak', suitable for the fresh market, and 'Kabaasi', suitable for drying and also fresh market. These cultivars were grafted on apricot seedling and were 5 years old when investigated in this research.

Frost Hardiness of some Turkish Apricot Cultivars during the Bloom Period