Determination of chilling and heat requirements of 69 Japanese apricot cultivars

• It will be valuable in the selection of the appropriate cultivars for producers and to avoid losses caused by an inadequate cultivar selection in a particular area by determining the chilling and heat requirement in large amount of Japanese apricot cultivars.
• We observed that the heat requirements of Japanese apricot had no obvious relationship with their origins.
• Cultivars with lower or higher chilling requirement are not suitable for introduction of Nanjing due to their abnormal phenotypes in the field.
• We provided a potential selection for cultivation distribution of Japanese apricot in China based on the determination of chilling and heat requirement in the ‘National Field Genebank for Japanese Apricot’.

Chilling requirement, together with heat requirement, which has an impact on the climatic distribution of the genotypes of tree species, determines the flowering date. It also played an important role in the protected cultivation of fruit trees. In our study, we estimated chilling requirements for breaking of dormancy and heat requirements for flowering for 2 successive years in 69 Japanese apricot cultivars of Nanjing (China). The chilling requirements of those Japanese apricot cultivars ranged from 24 to 82 chill portions according to the dynamic model, and the heat requirements of those cultivars fluctuated between 691.9 and 2634.7 growing degree hours. The Japanese apricot cultivars were classified into three groups according to their chilling requirements: the low chilling requirement cultivars with less than 50 chill portions, the medium chilling requirement cultivar ranging from 50 to 70 chill portions, and the high chilling requirement cultivars with more than 70 chill portions. In our study, cultivars originated in Guangdong of China generally have a low chilling requirements, and originated in Zhejiang and Jiangsu of China have a high chilling requirements. Cultivars with lower or higher chilling requirement are not suitable for introduction of Nanjing due to their abnormal phenotype. We also observed that the heat requirement of Japanese apricot had no obvious relationship with their origins. The determination of chilling requirements of 69 Japanese apricot cultivars provided some basis for their rationalized introduction and distribution, and was also important in a breeding program. Those results also expanded our understanding of the temperature responses of flower bud in Japanese apricot during the dormancy progress.