evaluation of early spring frost damage in different types of almond and apricot caltivars

in fruit trees damage of frost and freezing is depended to time of chillhng and tree phonological stage. almond (prunus amygdalus b. (and apricot (p. armeniaca l.) cultivars are usually the first fruit trees to bloom and susceptible to damaging frosts in the early spring. a study was conducted on different types of almond and apricot cultivars in order to investigation the main factors related to frosting, irregular of productivity and low crop load of trees for 10 years. six almond cultivars; sahand, a200, shkoofeh (very late bloom), touno, super nova (late bloom and self- compatibility), managa (early bloom) and 6 apricot cultivars; canino, royal, telton (self- compatibility), ordbad, nasiri and asgarabad (self- incompatibility) were evaluated for aspects of some biological and physiological characteristics that related to frost tolerance and fruit set. the results of 10 years evaluation showed that some cultivars despite were resistant to spring frost and usually their crop load was optimum. in addition of freezing damage, other factors like; undesirable climatic conditions in flowering time, direct or indirect influence on bearing and fruit set. touno and super nova as self compatibility and late blooming almond cultivars, canino, royal and tilton as self- compatibility apricot cultivars were tolerant to cool and unfavorable climatic conditions in early spring. therefore, they usually had higher and regular productivity. this differences were related to some phonological and physiological characteristics like; time of flowering, interior components of flower buds, time of niter and period of dormancy, temperature reaction of flower buds, effective pollination period, self – compatibility, frost resistance of pistils and flowers.