Abstract:

Flowers and fruits collected from the two major apple varieties (‘Gala’ and ‘Fuji’) grown in Ningxia during the bud, full-bloom, fruiting and young fruit setting stages were used as test material for the cryogenic treatments, and then the freezing rates of the ovaries under different cryogenic treatments were counted and analyzed. The Logistic equations established for the 20%, 50% and 80% freeze rates were set as the indicators of light, moderate and severe frost damage, respectively. The daily minimum temperature data collected in 19 meteorological stations from 1981 to 2022 were used to analyze the scope, frequency, intensity, and risk characteristics of disaster−causing factors of frost occurrence in Ningxia from the point of view of climatic disaster, by the means of mathematical statistics and spatial analysis. The classification of frost risk was completed by analyzing the difference in risk of late frost damage to apples in various regions of Ningxia, based on a combination of the vulnerability index and the exposure index of the affected apple. The results showed that the late frost damage to ‘Gala’ and ‘Fuji’ apple in Ningxia often occurred between 20 April and 10 May during the flowering and fruit setting period. The high−risk areas of late frost damage to ‘Gala’ and ‘Fuji’ apple were mainly located in the south-central areas close to the mountain ranges, among which Jingyuan, Xiji, and Longde were the highest risk areas, with a risk index of H_i＞0.3. The suitable areas for apple cultivation were mainly in Pingluo, the southeastern part of Yinchuan, the Litong district of Wuzhong, the western part of Linwu, and parts of Zhongwei city, with an exposure index of 0.7−1.0. The high risk areas for ‘Gala’ were located in the western part of Lingwu, the western part of Shapotou, and the central parts of Zhongning county in the northern Ningxia, and Xiji county and Longde county in the southern Ningxia. The high risk area for Fuji was located in the western part of Lingwu, Xiji county and most part of Longde county. Unsuitable areas for ‘Gala’ and ‘Fuji’ apple were mainly located along the Helan, Luoshan, Nanhua and Liupan mountain areas. In terms of frost resistance, Gala apple is stronger than ‘Fuji’ apple, and the resistance of ‘Gala’ apple is decreasing as the phenology evolves, since the phenological phase of ‘Gala’ is earlier than that of ‘Fuji’ apple. According to the frost damage zoning maps, ‘Gala’ is in higher risk than ‘Fuji’. The zoning results reflected the actual distribution of late frost risk for ‘Gala’ and ‘Fuji’ apple cultivated in Ningxia. The zoning map is providing a scientific baseline for the proper distribution of apply cultivation as well as for the disaster prevention and mitigation in Ningxia.

Key words: Apple, Frost resistance, Late frost, Risk zoning