Research On Fruit-dropping Characteristic And Ecological Mechanism Of Sweet Cherry(Prunus Avium)

In order to deal with the serious problem of physiological fruit dropping of sweet cherry?Prunus avium?in western Guizhou,the characters of fruit dropping of four five-year-old sweet cherry cultivars,i.e.‘Santina',‘Brooks',‘Sparkerry'and‘Black Pearl',were investigated using field trials and laboratory test method in the current work.By determination the pollen morphology characters and germination ratios,observation the anatomical observation of stalk abscission zones,investigation the characters of flowers and fruit dropping characteristic,quantification of carbohydrates and endogenous hormones,therefore,the charecters and physilolgical mechanism of sweet cherry fruit dropping in western Guizhou were unraveled previously.In addition,the effect of‘Zhuangguodiling'on reduce the physiological fruit dropping was also illustrated,the results are as follows:1.It was demonstrated that pollen germination rate were significant distinct among four sweet cherry,‘Brooks'cultivar was the highest,at 34.44%,followed by‘Sparkerry'and‘Black Pearl',were 27.94%and 7.22%respectively,while‘Santina'was the lowest just only 6.25%.the pollen germination of‘Brooks'was obvious higher than that of‘Sparkerry',and were all significance higher than the other cultivars,however,there was no obvious difference between‘Black Pearl'and‘Santina'.2.In addition,it was found that the shape of four sweet cherry pollen grains were all spheroidal under SEM.However,there were some discrepancies in morphological parameters,i.e.equatorial-length?E?,polar-length?P?and the ratio of equatorial-length to polar-length?E/P?,of four pollen grains cultivars.As a consequence,the E of‘Brooks'pollen grain cultivar was significant higher than the other three cultivars,about 26.6?m.The E of‘Santina'and‘Sparkerry'as well as‘Black Pearl'cultivars were 21.5?m,22.2?m,20.6?m,respectively,and there were no remarkable difference in E of pollen grains among these three cultivars.Moreover,regarding the P of different pollen grains,‘Brooks'and‘Sparkerry'cultivars were53.6?m and 50.3?m respectively and obvious higher than‘Santina'and‘Black Pearl'cultivars,which were approximately 43.8?m and 42.0?m respectively.Conversely,the order of the ratio of E/P of four pollen grain cultivars was the‘Black Pearl',‘Brooks',‘Santina',then‘Sparkerry',which were approximately 0.496,0.495,0.491and 0.442,respectively and‘Sparkerry'cultivar was obvious lower than the other cultivars.Furthermore,correlation analysis showed that pollen germination rate was positively correlated with P of pollen grain?P?0.01?and E of pollen grain?P?0.05?,while was negatively correlated with ultimate abscission rate?P?0.01?.Additionally,the P of pollen grain was negatively correlated with the ultimate abscission rate?P?0.01?.Whereas the ultimate abscission rate has no significant correlativity with E and E/P of pollen grain.It seem illustrated that greater of the pollen grain volume stored more rich nutrients,therefore,is beneficial to fruit setting.3.It was also demonstrated that fruit dropping pattern were difference among four sweet cherry cultivars.Taken together,the initial blooming date of four cultivars synchronously occurred on about March 28,and the abscission peak of flower occurred on around April 18.However,the physiological abscission pattern of fruit diversified among the four cultivars,i.e.the‘Santina'and‘Sparkerry'were characterized in two peaks of fruit abscission approximately on May 18 and May 28,respectively.Whereas the two peaks of‘Black Pearl'occurred about on May 8 and May 28,respectively,and the two periods presented on‘Brooks'approximately on April 28 and May 28,respectively.Furthermore,the ultimate abscission rate were difference among four sweet cherry cultivars,i.e.‘Black Pearl'showed the highest abscission rate?91.5%?,followed by that of‘Santina'?89.3%?,and‘Sparkerry'?82.2%?or‘Brooks'?80.7%?were the lowest,and‘Black Pearl'and‘Santina'cultivars were obvious higher than of the other cultivars,however,there was no significant difference between‘Sparkerry'and‘Brooks'.In addition,the results of spraying‘Zhuangguodiling'in‘Santina'cultivar at bloom period showed that the ultimate fruit abscission of untreated plant was remarkably higher than the plant after treatment?84.2%?.It seem demonstrated that the effective function of‘Zhuangguodiling'on reducing physiological fruit dropping in sweet cherry.4.By anatomical comparison of fruit stalk abscission zone between dropped and retention fruit,it was clearly indicated that fruit pedicel where fruit dropping directly takes place and there were clearly anatomical differences between retention and dropped fruit pedicel abscission,i.e.paraffin section staining and the cell density.The paraffin section staining of the dropped fruit stalk abscission zone was relatively shallower than that of the corresponding zone of retention fruit pedicel.Moreover,the cell number of each microscopic field of abscission zone on dropped fruit pedicel at the first massive fruit dropping period was significant higher than that at the second massive fruit dropping,conversely,no significant difference was investigated from the retention fruit.5.From the rapid expansion period of fruit?April 28?to fruit maturation period?May 28?,the glucose and fructose contents of four sweet cherry cultivars in retention fruit appeared an ascending trend,however,the dynamic fluctuations in dropped fruit presented a curve of‘up–down–up'with the development of fruit.In addition,the content levels of glucose and fructose in retention fruit were always significant higher than that of dropped fruit.For sucrose,although the concentration in retention and dropped fruit illustrated an ascending trend with the development of fruit,meanwhile,there were no obvious difference in its levels between retention and dropped fruit,however,it was always appeared a phenomenon of retention fruit relative higher than that of dropped fruit.Therefore,we could speculate that glucose and fructose in dropped fruit do not reach the required threshold possibly was a vital reason that led to fruit abscission.6.In retention fruit,dynamic changes of CTK in‘Santina'cultivars was from high to low,to high again,with the development of fruit,however,the change tendency of CTK in dropped fruit exhibit entirely downtrend,moreover,the content levels of CTK in retention fruit were always higher than that of dropped fruit.The change tendency of GA₃ in retention fruit was similar with dropped fruit,which exhibit entirely downtrend with the advancement of fruit dropping,however,the contents of GA₃ in retention fruit was significant higher than dropped fruit for the development of fruit.Levels of IAA in retention fruit tend to increase with the development of fruit,while in dropped fruit,it showed a declining trend after rising and declining again.In addition,throughout the fruit development period,the contents of IAA in retention fruit were obvious higher than that of dropped fruit,except for the initial stage of fruit development.The changes of ABA content in retention fruit was on a rising tendency,while in dropped fruit presented a curve of‘high–low–high',Furthermore,the contents of ABA in retention fruit was significant higher than dropped fruit with the development.Additionally,the ratio of?GA₃+IAA+CTK?/ABA presented a completely opposite tendency for the whole development of fruit:in retention fruit,the fluctuations exhibited a curve of‘up-down-up',whereas in dropped fruit,the changes was from high to low,to high again with the development of fruit.Additionally,the ratio in retention fruit was higher than that of dropped fruit.Thus,the disharmony of plant hormones in fruit was another possible element caused fruit dropping in sweet cherry.