Abstract: 【Objective】Sweet cherry (Pruns avium L) originated in Europe, is the earliest mature deciduous fruit tree in the north of China, famous for "the first spring fruit". With the rapid development of sweet cherry production in the 1990s, its cultivation range and quantity have been greatly expanded. It was reported that sweet cherry couled been obtained stable and high yield in the high altitude region in southwest China, which had been classified as a suitable planting area for sweet cherry. Now sweet cherry has also become an emerging industry for farmers in high altitude cold region to generate income. It can be seen that the high altitude areas in the south China with similar habitats also have the climatic conditions for successful cultivation of sweet cherries. Flowers are the reproductive organs of plants, the quantity of flower bud development are closely related to the fruit traits and yield at fruiting stage. Carbohydrate is an important material basis for flower bud development. Flower bud differentiation of sweet cherry goes through three stages: physiological differentiation, morphological differentiation and flower organ formation, amongwhich flower organ formation occurs in the spring of the following year after winter dormancy. As a typical fruit tree with first flowering and then leaf, the energy and material required for flower organ development in spring of sweet cherry depend on the accumulation of nutrients within the tree in the previous growing season. Therefore, the study of carbohydrate contents and endogenous hormone levels in the flower bud during dormancy, especially before the flower bud sprouting, has certain guidance for the analysis of flower bud quality and following yield. In this paper, the difference of carbohydrate content and endogenous hormone level in flower buds of sweet cherry at different altitudes in Hangzhou area were compared, in order to reveal the reason of low yield of sweet cherry in low altitude region of Hangzhou from the physiological level. 【Method】Five-tree aged sweet cherry grown respectively at high and low altitudes in Hangzhou were used as the experimental materials. Firstly, the deciduous period and germination period of sweet cherry varieties in two regions were observed for past three years. On this basis, from November 2021 to March 2022, flower buds were collected before dormancy (1 month before complete leaf fall), during dormancy (1 month after complete leaf fall), and before budbreak (when flower buds just emerged red) to determine the relevant physiological indexes. The carbohydrate indices (such as starch content, different sugar component content, soluble protein content, free amino content) and endogenous hormones indices (such as GAs, IAA, ABA, CTKS) were determined of three stages. The flower bud weight was investigated, too. Finally, the content levels of flower buds at different stages were analyzed by principal component analysis. Grey relation analysis(GRA) and GRA-SVM model were used to analyze the correlation degree between flower bud weight and the flower bud inclusion index.【Result】The results revealed that after dormancy, the content of starch and free amino acid in flower buds increased, while the content of soluble protein decreased. Before budbreak, the content of free amino acids in sweet cherry flower buds in high altitude was 1.22 times that in low altitude, but there was no significant difference in soluble protein content between the two regions. The variation trend of the four sugar components was the same, but the content of individual sugar components varied greatly among regions. Sucrose and sorbitol are the dominant sugar components in sweet cherry flower buds. Before budbreak, there was no significant difference in sucrose and glucose content between two regions, but the sorbitol content in high altitude was significantly higher than that in low altitude. The contents of sorbitol, fructose and glucose were 1.21, 1.18 and 1.11 times of the value in high altitude, respectively. In terms of endogenous hormones, the content of ABA was the highest, followed by IAA, and the content of GAs was the lowest. Among CTKs, iPA content was lower and DHZR content was higher in flower buds of sweet cherry in two regions. The content of CTKs and GAs in high altitude was 1.22 and 1.19 times of the low altitude value, respectively, while the content of ABA in low altitude was 1.07 times of the value in high altitude. The CTKs/GAs values in flower buds of two regions were significantly different. The value of the high altitude was still 1.02 times higher than that of the low altitude. There was no significant difference in the weight of single flower bud in the three stages. After dormancy, the weight of single flower bud increased in both regions, and the value of high altitude was slightly higher than that of low altitude. From the appearance observation, it could be seen that the flower bud scales of sweet cherry in two regions were tightly wrapped, but the flower bud of sweet cherry in high altitude was fuller. Principal component analysis showed that the content level of sweet cherry flower buds in high altitude was lower before dormancy. After the accumulation of dormancy period, the content level of flower bud in high altitude was higher than that in low altitude. Before budbreak, the content level in high altitude was still higher than the low altitude. GRA analysis showed that the correlation degree between flower bud inclusions and weight was not same at different stages. The correlation coefficient between the inclusions and the weight of the flower buds was larger before budbreak. After comprehensive analysis of the whole stage data, it could be seen that the top five factors of correlation coefficient with flower bud weight belonged to GAs, starch, glucose and CTKs respectively. GRA-SVM model also confirmed that there was a certain coefficient correlation between flower bud weight and the selected factors.【Conclusion】The changes of flower bud contents in different dormancy stages of sweet cherry in two regions were basically the same, but the contents were different. The overall level of flower bud inclusions in high altitude area of Hangzhou was higher than that in low altitude area. Combined with GRA-SVM model, it could be further revealed that the low level of some inclusions was the internal physiological reason for the low flower bud weight of sweet cherry.
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