Abstract Due to study, the rate of relative resistance is studied on some peach and nectarine cultivars at sudden downfall of temperature and extreme cold, in natural weather conditions of winter season of Mashhad city in 2008. Meteorology station of studied area (Golmakan station) registered - 22°C for minimum abstract temperature of this year in 13th January that it had difference to Mashhad weather a little. This test is performed as factorials at form randomize complete block design with three replications. Relative ionic leakage and visual observations are 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 studied peach and nectarine cultivars, Mashhad Sorkhosephid and Mashhad Ghermez cultivars, that they are Iran native cultivars, 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 pertained to nectarine Indipendense cultivar and the most resistance of vegetative buds pertained to Mashhad Sorkhosephid and Redhaven in peach cultivars and Nectared 6 and Qiuta cultivars in nectarine cultivars. Relative ionic leakage of annual wood in peach cultivars was more than nectarine cultivars.

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