The rate of relative resistance of some peach and nectarine cultivars at sudden downfall of temperature and extreme cold of Mashhad in 2008 were studied. Meteorology station of studied area (Golmakan station) registered -22°C for minimum abstract temperature of this year in 13th January. This test is performed as factorials at form randomize complete block design with three replications. Relative ionic leakage is used on reproductive and vegetative buds, annual and biennial wood in peach cultivars (J.H.Hale, Elberta, Redhaven, Mashhad Sorkhosepfide and Mashhad Ghermez) and nectarine cultivars (Indipendens, Qiuota, Nectared 6 and Stargold). Between the studied cultivars, the Iranian local cultivars, Mashhad Sorkhosephid and Mashhad Ghermez had the most resistance reproductive buds that haven\\\'t got significant difference than other peach and nectarine cultivars exception Indipendense cultivar. The most sensitive of reproductive buds of Indipendense nectarin cultivar and the most resistance of vegetative buds pertained to Mashhad Sorkhosephid and Redhaven peach cultivars and Nectared 6 and Qiuta cultivars. Relative ionic leakage of annual wood in peach cultivars was more than nectarine cultivars, but relative ionic leakage between peach cultivars wasn\\\'t significant and Nectared 6 cultivar hadn\\\'t difference to peach cultivars. Cold hardiness of annual and biennial wood in peach and nectarine cultivars was more than vegetative and reproductive buds

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