| Citrus is the world’s largest fruit crop, and China is the world’s largest citrus-producing country. However, china’s citrus ripe stage mostly concentrated around December resulting in the seasonal and regional citrus fruit producing, which did not help to marketable. So adjusting maturity structure played an important role of Chinese citrus industry developing rapidly according to the plan of our country citrus industry development. Banphil navel orange is a late-maturing variety from the mutant of Washington navel orange by Australia, and Chongqing Henghe Fruit Company imported it from Australia in 2002. By now it has been mainly planted in Jiangjin and Fengjie in Chongqing. And these helped to improve the mature structures of Chongqing citrus industry. However, the lack of ecological adaptability and the cultivation techniques result in lower yield and economic benefits of this variety. In Chongqing, the flowers, fruits, winter fruits dropping and uneven quality of late-maturing navel orange showed a greater difference in the different ecological conditions. In this study, we carried out the physiological response of late-maturing navel orange flowers and young fruit shedding under different ecological conditions in order to understand the physiological mechanism of late-maturing navel orange fruiting and dropping and provide a basis for high-quality high-yield cultivation techniques. The main results as follows:1. The dynamic changes of flowering, fruiting and dropping were measured under two Chongqing typical different weather conditions of Jiangjin with warm winter, wet summer and few bright sunshine and Fengjie with cool winter, more sunshine, drier climate conditions. The results showed that the dynamic changes of late-maturing navel orange flowering, fruiting and dropping under these two different weather conditions were very different. The number of flower per plant at Fengjie is much higher than at Jiangjin by 115.5%, which laid the basis of high yield of the late-maturing navel orange at Fengjie. Whilst, the first physiological fruit dropping of Fengjie more serious than that of Jiangjin, however, the second physiological fruit dropping of Jiangjin was more serious than that of Fengjie. The above results indicated that the Fengjie weather condition with cool winter, more sunshine, relate lower humidity help to late-maturing navel orange flowering and fruiting.2. The results showed that the number of fruit setting per plant of Bamfild navel orange at Jiangjin and Fengjie orchard were significantly different. The flower and fruit capacity per plant of Bamfild navel orange at Fengjie orchard is always higher than Jiangjin, after the first physiological fruit drop, the fruit setting per plant at Jiangjin is 700.9, while that is up to 758.6 at Fengjie, which is 8.23% higher than Jiangjin; and after the second physiological fruit drop, the fruit setting per plant at Jiangjin is 54.1, while the Fengjie’s is up to 182.6,the average per plant fruiting is 237.5% higher than Jiangjin, Which indicated that the fruit setting ability of Bamfild navel orange in the second physiological fruit drop period at Fengjie region was higher than that of Jiangjin region. The results suggested that the response of fruit setting ability of Bamfild navel orange on different ecological environmental was significantly different and citrus fruiting capacity was mainly determined by the fruit setting ability at the second physiological fruit drop period. The correlation analysis also showed that the second physiological fruit drop period after flowering was a significant negative correlation with final fruiting number and the fruit number of per unit volume of citrus tree.3. In this study, we found that carbohydrate metabolism of fruit had a significant correlation with fruit dropping. And the dropped fruits of BanPhil navel orange had a higher fruit fructose content than normal fruits during both the two physiological fruit dropping stages. In contrast, the glucose content in the normal fruit at the first fruit dropping stage was significantly higher than dropping fruit, whilst the content of sugar and starch in normal and dropping fruits had no significant difference. However, the content of glucose, sucrose and starch in normal fruits were significantly higher than in dropping fruits during the second physiological fruit dropping stage. This result indicated that the accumulation of fructose in young fruits may not be conducive to BanPhil navel orange fruiting, however, glucose and sucrose enriched in fruit have an important impact on lowering the fruit dropping of BanPhil navel orange.4. The carbohydrate content of leaves and the normal fruits in citrus were determined, the results showed that the contents of sucrose and starch in leaves of Jiangjin area were much higher than that of the Fengjie area during the second physiological fruit drop period. The correlation analysis of physiological dropping, fruiting ability and the content of carbohydrate of leaves before anthesis of citrus were showed that the total amount of flowers and starch content in leaves was significantly positive correlation, while the total amount of flowers compare with the ratio of the second physiological dropping was significantly negative correlation, which indicated that too much flowers will consume lots of carbohydrate, which led to the content of carbohydrate decrease after the first physiological dropping,and the strength of the second physiological dropping is possible intensity correlation with fixed carbohydrate by photosynthesis. The multiple linear regression model of the fruit number of per unit volume of trees (Y) and the carbohydrate content (X1 glucose, X2 starch, X3 fructose) of leaves before anthesis period is Y=4.747+21.644X1+0.969X2-133.207X3, R=0.669**. The results of significance tests on the regression equations and regression coefficients showed that the factors of X1, X2, X3 are Significant difference at 0.01 level.5. The abscisic acid (ABA) content in dropping fruits during both the two physiological fruit dropping stages was significantly higher than in normal fruit, whist, the endogenous hormone gibberellic acid (GA3), auxin (IAA) andzeatin (ZR) levels in normal fruits were significantly higher than in dropping fruit during the first physiological fruit dropping stage, and the endogenous hormone gibberellic acid (GA3) and zeatin (ZR) levels in normal fruits were significantly higher than in dropping fruits during the second physiological fruit dropping stage.The ratio of ABA and GA3+IAA+ZT of dropping fruits were higher than that of normal fruits, the imbalance of endogenous hormone relationship is the main reason for fruit drop. |
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