Chilling and heat requirements of 103 germplasms of peach in Nanjing

Abstract: 【Objective】Chilling requirement (CR) and Heat requirement (HR) are important phenologi-cal traits of temperate deciduous fruit trees, and the amount of them varies with different species, and al-so varies with different varieties within the same species. For peach（Prunus persica L.）, the CR of 660 germplasm resources have been evaluated, while only 70 resources’HR have been evaluated so far.Meanwhile, systematic comparison and correlation analysis of the CR and HR of floral buds and leaf buds using large peach samples have not been reported. In this research, different estimation models were used to calculate the CR and HR of 103 peach germplasm resources in Nanjing, to compare the CR and HR in floral and leaf buds and to explore the correlation between the CR and HR with flores-cence and leaf expanding.【Methods】Nov. 2018 to Apr. 2019-04 (average temperature was 8.79 ℃) and Nov. 2019 to Apr. 2020 (average temperature was 12.06 ℃), the CR for initial blooming and leaf bud breaking of 103 peach germplasm resources in Nanjing (southeast China, 31°14’N 118°22’E) were studied by 2 estimation models, including growing degree hours model and effective temperature model. Analysis of the CR and HR of floral and leaf buds, and the correlation between the requirements and blooming and leaf expanding dates were conducted.【Results】The rangs of terminal stage of natural dormancy, blooming stage and leaf expansion stage among the 103 varieties were wide. The terminal stage of natural dormancy were between 1st Dec. And 15 th Mar., and blooming stage and leaf expansion stage were between 24th Feb. and 3rd Apr., and between 3rd Mar. and 7th Apr., respectively. The CRs of flo-ral and leaf buds calculated by 0-7.2 ℃ model (RSD were 6.74% and 7.93% for floral and leaf buds, re-spectively) were consistent in two years, while there were great difference in the results of different years calculated by 7.2 ℃ model, its RSD were 9.88% and 9.57% for floral and leaf buds respectively,and the RSD of floral buds’CR was significantly higher than those obtained by 0-7.2 ℃ model (p ＜0.01). Utah model couldn’t be used for low chilling requirement varieties or determining the starting date of low temperature accumulation. The HRs of floral and leaf buds calculated by effectuve temperature model (RSD were 9.05% and 5.68% for floral and leaf buds, respectively) were consistent in two years, there were also great difference in the results of different years obtained by growing degree hours model, its RSD were 10.55% and 14.61% for floral and leaf buds, respectively, and the RSD of leaf buds’HR was significantly higher than those calculated by effective temperature model (p ＜ 0.01).Therefore, 0-7.2 ℃model and effective temperature model were more suitable for assessing the CR and the HR respectively in Nanjing area. The ranges of the CR and HR among the 103 varieties were wide,in which CRs of floral buds were between 151 and 1 264 h, and of leaf buds were between 187 and 1 108 h according to 0-7.2 ℃model. The HRs of floral buds were between 256 and 391 D·℃ and of leaf buds were between 267 and 498 D ·℃ according to effective temperature model. We obtained some peach materials with low CR, including‘Yingchun’and‘Xialingbei 1’, as well as some peach materi-als with high CR, including‘Feicheng 51-28’,‘Xiangtao’and‘Juhuatao’. and slso we obtained some materials with low HR, including‘Xinjianghuangrou’,‘Yingqing’and‘Honghuashantao’, as well as some peach materials whit high HR,including‘Xinjiangdatianren’,‘Qingyedongtao’and‘Huayu’.The floral buds had almost the same CR with the leaf buds, with some exceptions, the leaf buds of‘Zhouxingshantao’and‘Honghuashantao’had CR about 5 times higher than that of the floral buds. The HR of the leaf buds was generally higher than what of the floral buds, for example, the HRs in leaf buds of‘Juhuatao’and‘Kashiliguang’were 1.5 times as high as those of their floral buds. There was no significant correlation between the CR and the HR in peach buds. Both the CR and the HR were re- lated to the blooming date and leaf expansion date, the lower the CR and the HR, the earlier the dates of blooming and leaf expanding, While the higher the requirement, the later the dates of blooming and leaf expanding.【Conclusion】0-7.2 ℃ model and effective temperature model were more suitable for assess-ing the CR and the HR of peach in Nanjing area; The 103 peach varieties had wide ranges of the CR and the HR; The floral buds had almost the same CR with leaf buds, but had lower HR than the that ofleaf buds’; There was no significant correlation between the CR and the HR, and both the CR and the HR played important roles in blooming and leaf expanding.