an investigation on freezing tolerance of peach and nectarine reproductive buds in controlled conditions

damage caused by freezing can be the result of differences in cellular processes, including changes in membrane properties, interactions between macromolecular and enzymatic reactions. in this experiment, total soluble solids (tss) and relative water content of the reproductive buds of cultivars “j. h. hale”, “elberta,” “redhaven, ” “sorkh sefid mashhad” and “amsden” peaches, along with nectarines: “independence”, “kuota”, “stargold” and “nectard no:6”, were evaluated in the months october, november, january, february and march 2009 under natural conditions. extent of orchard electrolyte leakage, the level of lt50 (i.e. the temperature killing 50 percent of the sample) and total soluble sugar of the cultivars were assessed under controlled conditions in february 2009. results showed that in february and under natural conditions, the total soluble sugars of peach and nectarine cultivars, in february were more than those at the other times and the relative water content in all the peach and nectarine cultivars increased with approaching the time of bud opening in march. in controlled conditions, by reduction of temperature, amount of electrolyte leakage intensified while the total soluble sugars decreased . also, the level of resistance in peaches and nectarine cultivars varied, so that “sorkh sefid mashhad”, “redhaven” and “amsden” peach cultivars as well as “starglod” and “nectared 6”, nectarine cultivars had the highest resistance to winter freezing conditions in the month of february.