Study On The Fruit Growth And Development And The Effect Of Exogenous ABA On Fruit Quality Of Citrus Grandis Cv. ’Hongroumiyou’ And ’Sanhongmiyou’

Sichuan Province is one of the important production areas of Citrus grandis（L.）Osbeck.However,there were some problems such as unreasonable variety structure,low yield and low-efficiency in the pummelo productions.Our research team has introduced new pummelo varieties from Fujian Province.Compared with the original production area Pinghe,Fujian,the harvest time has been delayed with the decrease of granulation of the fruit segments,which promots the farmers’income.However,the fruits revealed relatively low sugar accumulation and high acid contents compared with in Fujian due to the lower annual average temperature and less mean annual sunshine durations.In this study,we explored the external fruit quality,sugar and acid content and their metabolism-related enzyme activities,as well as their correlation during fruit growth and development of’Hongroumiyou’and’Sanhongmiyou’.Then we analyzed the effect of sparying exogenous abscisic acid（ABA）on the fruit quality and sugar and acid metabolism at the late development of fruit.The results suggested the optimal concentration and period of ABA treatment,which provided practical guidance for improving fruit quality of pomelo.The main results are listed are as follows.i.During the growth and development of’Hongroumiyou’and’Sanhongmiyou’,thelongititual and transverse diameter,weight per fruit and flesh weight reveale a single’S’type change trend from 30 to 90 days after flowering.Then the fruits show faster growth from 150 to 180 days after flowering.The peel thickness has a decrease and ebilbe rate shows an increase when the fruits are ripening.The flesh weight accounts for 72%and 74%of mature fruits in’Hongroumiyou’and’Sanhongmiyou’.ii.The total soluble solid content keeps a rise change during the fruit development stages,which reaches the maximum of 10.78%and 11.63%in’Hongroumiyou’and’Sanhongmiyou’at 190 days after flowering,revealing significant difference between two cultivars.The vitamin C content shows a rapid increase trend from 40 to 160 days,then has a slow decrease change,with the value of 28.75 and 25.12 mg·100g^-1 in the mature fruits of’Hongroumiyou’and’Sanhongmiyou’.iii.The sugar of the mature fruits consists of fructose,glucose and sucrose with the proporation of 6.7:2.0:1.3 and 6.3:1.7:2.0 in’Hongroumiyou’and’Sanhongmiyou’,respectively.The sugar content shows an increase from 40 to 140 days after flowering and then has a decrease.The accumulation of sucrose is positively correlated with the activity of sucrose synthase synthetic direction（SSs）and sucrose phosphate synthase（SPS）,whereas is negatively correlated with invertase（AI,NI）and sucrose synthase cleavage direction（SSc）.iv.The organic acid is composed of citric acid,oxalic acid,tartaric acid,malic acid and quinic acid.Citric acid is the most component,accounting for 67%and 73%of organic acid in’Hongrou miyou’and’Sanhong miyou’.The citric acid content reveals a rise and then decrease change during the fruit development.There is a significant positive correlation between citric acid with citrate synthase（CS）and phosphoenolpy-ruvate carboxykinase（PEPC）activities,while negative correlation with malate dehydrogenase（MDH）,isocitrate dehydrotenase（IDH）and aconitase（ACO）.v.Sparying exogenous ABA has significant effects on fruit quality,sugar and acid components of’Hongroumiyou’and’Sanhongmiyou’.By comprehensive evaluation on ten internal fruit quality using the method of subordinative function value,we suggest that spraying 2.5 mmol·L^-1 of ABA at 130 days,and 0.5 mmol·L^-1 of ABA at 150 days after flowering for’Hongroumiyou’and’Sanhongmiyou’can obviously improve their fruit qualities.This will provide basis for high-quality and high-efficient production of pummelo cultivars.