A Preliminary Study On Development Difference In Fruit From Upper And Lower Inflorescence Of Rabbiteye Blueberry And Its Formation Mechanism

Vaccinium spp.（also called blueberry）is a genus of perennial shrub of the family Ericaceae,which bears fruit rich in functional substances with high food and health value.Rabbiteye blueberry（Vaccinium ashei）is one of the main blueberry varieties in the south of China.Due to the large numbers of flowers and fruits,there are some problems in production such as too small fruits or different fruit sizes.We study the development difference in fruit from upper and lower inflorescence of rabbiteye blueberry and its formation mechanism,which can provide a basis for flower and fruit thinning,harvest by stages,and regulation of fruit development and maturity in blueberry production.The differences in growth and development,and quality changes in fruit from upper and lower inflorescence,and photosynthetic characteristics were investigated in the four rabbiteye blueberry cultivars,‘Brightwell’,‘Climax’,‘Powderblue’and‘Tifblue’.The results showed that,the weight per fruit from upper and lower inflorescence of the four rabbiteye blueberry cultivars all increased significantly from the coloring stage to the mature stage.Before the coloring stage,there was no significant difference in the weight per fruit from upper and lower inflorescence,but after the coloring stage,the size of fruit from the lower inflorescence was larger than that from the upper inflorescence.The results of Fuzzy comprehensive evaluation showed that the comprehensive quality in fruit from lower inflorescence of‘Brightwell’,‘Climax’,‘Powderblue’and‘Tifblue’was better than that from upper inflorescence.The comprehensive evaluation results of principal component analysis showed that the quality in fruit from lower inflorescence of four rabbiteye blueberries were better than that from upper inflorescence,and the top three in terms of comprehensive quality are‘Brightwell’,‘Powderblue’and‘Climax’.The net photosynthetic rate,stomatal conductance and intercellular CO₂ concentration of‘Powderblue’were significantly higher than those from the other three rabbiteye blueberries.Furthermore,the net photosynthetic rate has significantly positively correlation with transpiration rate,and intercellular CO₂ concentration,respectively.The contents of photosynthetic pigments（chlorophyll a,b and carotenoids）in leaves of‘Powderblue’were equivalent to those in‘Brightwell’,and both were significantly higher than those from the other two rabbiteye blueberries.The results mentioned above suggested that the higher net photosynthetic rate of‘Powderblue’was mainly determined by stomatal factors,followed by non-stomatal factors such as photosynthetic pigment.The changes of endogenous hormones were investigated in the early and late stage of fruit development of rabbiteye blueberry‘Brightwell’and southern highbush blueberry‘O’Neal’.The results showed that,In the early stage of fruit development,IAA and ABA concentrations in fruit of‘O’Neal’was significantly higher than those in‘Brightwell’,but the concentrations of GA and SA in fruit of‘O’Neal’were significantly lower than those in‘Brightwell’.These suggested that the fruit growth and development of‘O’Neal’was earlier than that of‘Brightwell’,which was closely related to the higher IAA and ABA concentrations,and lower GA and SA concentrations in the former than those in the latter.In addition,the lower ABA and JA and higher SA concentrations in fruit from upper inflorescence of‘O’Neal’than those from lower inflorescence,were one of the reasons for its faster growth and development in fruit from upper inflorescence than that from the lower inflorescence.At break stage of fruit development,the concentrations of IAA,ABA,GA and JA in fruit from lower inflorescence of‘Brightwell’were significantly higher than those from upper inflorescence.However,at fruit maturity stage,the concentrations of IAA,ABA and GA in fruit from lower inflorescence of‘Brightwell’were significantly lower than those from upper inflorescence.Thus,the fruit from lower inflorescence of‘Brightwell’blueberry develops faster and matures earlier than fruit from upper inflorescence,which maybe the result of the mutual balance and coordination of various endogenous hormones in fruit.