Chilling and heat requirements and bloom frost tolerance of Prunus scoparia (Spach) C. K. Schneid and P. elaeagnifolia Spach

Key message The flowering time of wild almond species studied herein is more influenced by heat requirement, which partly justifies also the differences in flowering date during the different years in genotypes. Bloom frost tolerance, chilling and heat requirements can influence distribution and productivity of almond species. Both laboratory and field-related methods were employed to determine the chilling and heat requirements as well as bloom frost tolerance of several early-, mid- and late-flowering genotypes of two wild almond species ( Prunus scoparia (Spach) C. K. Schneid and P. elaeagnifolia Spach). The variations of carbohydrates and soluble solids in the wood and buds were also measured during chilling period in laboratory method. Furthermore, the tolerance to spring-frost was evaluated using electrolyte leakage method. Results showed that in field method, the chilling requirement in P. scoparia ranged from 344 to 682 CU, whereas P. elaeagnifolia exhibited chilling requirements between 313 and 415 CU. The greatest chilling requirement was observed in the early-flowering genotype of P. scoparia. The heat requirement in P. scoparia ranged from 2737 to 9149 GDH, while this parameter varied from 4985 to 7788 GDH in P. elaeagnifolia . The highest heat requirement was observed in the late-flowering P. scoparia . The laboratory method failed to measure chilling and heat requirement of P. scoparia , due to sever bud abscission, but the chilling requirement of P. elaeagnifolia ranged from 383.33 to 450 h in this method, which was slightly higher than that of field method. Measurements of plants internal chemicals showed that prolonged duration of chilling is contributed to more extensive degradation of carbohydrates which results higher soluble solids' content. The highest tolerance to bloom frost was observed in the early-flowering P. elaeagnifolia (– 5.3 °C), while the lowest tolerance was recorded in the late-flowering P. scoparia (– 3.8 °C). There was a negative association between bloom’s frost tolerance and soluble solids' content.