There were no significant variation trends in the last dates of different freezing injury grades in Xunyi. The last date of severe freezing injury in Liquan showed a significant advance trend with an advance rate of 3.3d♱0y-1 (P<0.01), and the last dates of moderate and light freezing injury in Liquan showed no significant variation trends. The first apple flowering dates in Liquan and Xunyi advanced significantly from 1967 to 2018, with advance rates of 2.8d♱0y-1 (P<0.01) in Liquan and 0.8d♱0y-1 (P<0.05) in Xunyi, respectively. The results showed that the thermal time model could be used to reconstruct the first apple flowering dates in Liquan and Xunyi. The linear tendency method was used to analyze variation trends in the first flowering date, last date of three freezing injury grades, and freezing injury risk indices. The differences between the last date of three freezing injury grades and the first flowering date were defined as freezing injury risk indices. The daily minimum temperatures in the two sites during the same period were used to extract the last date of three freezing injury grades, in which the upper critical thresholds were-2, 0, and 2℃, respectively. ![]() To assess the risk of flowering freezing injury of Fuji apples in two main apple-producing counties of Liquan and Xunyi, Shaanxi province, the daily average temperature was used to reconstruct the apple first flowering dates during 1967-2018 in Liquan and Xunyi, using the thermal time model. ![]() Freezing injury during flowering has become one of the most serious natural disasters affecting the yield and quality of apples in Shaanxi. Shaanxi province is an advantageous ecological area for apple cultivation and a high-risk area of freezing injury during flowering.
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