New apricot (Prunus armeniaca L.) hybrids tolerant to spring frost

Damages caused by spring frosts are the most critical factor in reducing apricot production. The selection of cultivars tolerant to spring frost has been regarded as the most straightforward strategy to reduce late spring frost damages. To select frost-tolerant genotypes with suitable fruit quality, 1000 hybrids resulting from hybridization between two genotypes, Noori_Dirras×Rajabali, were evaluated for two years, 2020 and 2021, in the Agricultural Research Station of Bastam Shahroud. Phenological and pomological traits as well as spring frost tolerance were recorded naturally. Frost tolerance was determined by counting the number of healthy and damaged flowers or fruits on three random branches in each tree after the onset of frost. The last critical damaging temperatures in the first and second years occurred at -5 and -4 °C, respectively. Hybrids No. 7-74 with 60% and No. 12-64 with 41% tolerance of spring frost were identified as the most tolerant hybrids in the first and second years, respectively. Evaluation of the fruit of 51 tolerant genotypes in the second year showed that there was a great variety in the most traits among the offsprings. Ranges of 45 days to ripening, 37 g fruit weight, 13 ◦Brix total soluble solids, and 1.933 kg/cm2 fruit firmness were observed among the hybrids. A comparison of the two-year frost tolerance mean of hybrids showed that 10 hybrids, 7-74, 10-65, 11-43, 12-11, 12-31, 12-47, 12-64, 13-29 and 14-16 were superior compared to the commercial tolerant genotype (Jahangiri) and could be candidates for propagation and adaptation experiments to achieve frost-tolerant cultivar with good fruit quality.