Study Of Fruit Volatiles In Peach Germplasm Resources

Peach is an important economically fruit in our country’s horticulture and agricultural industry.Aroma is an important quality trait of peach fruit,which directly affects consumer preferences.In recent years,people have complained that peach fruits are becoming tasteless,the loss of flavor is an important factor.Fruit aroma comes from volatiles,and its composition and content are affected by genetics.This project uses different varieties peach fruits as materials,using HS-SPME and GC-MS techniques to detect volatiles,analyzing the correlation of volatiles with quality traits.Besides,using transcriptome sequencing(RNA-Seq)to identify genes related to the metabolism of volatiles in peach fruits and provide a basis for improvement of peach fruits.The main results are as follows:1.The content of volatiles in peach fruits of different germplasm showed varies greatly.According to the chemical structure,the volatiles of peach fruit mainly include aldehydes,alcohols,esters,lactones and terpenes.Take the 22 main volatiles in peach fruit as an example,including 6 lactones,3 esters,4 alcohols,3 aldehydes,2 terpenes,and 4 norisoprenoids.Based the formation of the aroma in peach fruits,the content ofγ-Decalactone and δ-Decalactone are changed more than 300 folds.Principal component analysis(PCA)and cluster analysis were found that peach fruits can be divided into 5 groups.The content of lactones in the peach fruits of group A accounted for 43.13%,showing a “peach flavor”,which includes a large number of flat peach varieties;the relative content of terpenes in the peach fruits of group B was 57.2%,showing a “floral flavor”,representative varieties include ‘Da Tuan Mi Lu’,‘Hu Jing Mi Lu’,‘Nong Lin 89’.The relative content of esters in group C is 33.56%,which is a“fruity flavor”,including a large amount of yellow fleshed peach;the content of C6 compounds,esters,and terpenes in the peach fruits of group D are relatively high,showing a “mixed flavor”;the content of C6 compounds in the fruits of group E accounted for 55.58%,showing a “green flavor”.2.The content of volatile is correlated with other quality traits in peach fruit.Based on the analysis of the volatiles in varieties peach fruits,this study also analyzed the relationship of fruit weight,shape,flesh color,texture,mature time with volatiles.The results showed that:(1)With the increase of fruit weight,the content of volatiles showed a decreasing trend.The aroma content of peach fruit has a significant negative correlation with fruit weight,and the correlation coefficient is-0.26(P<0.05).For example,the fruit weight of ‘Nan Jing Bai Sha’ is 51.05 g,and the total volatiles is3938.91 ng/g;the fruit weight of ‘Yoshihime’ is 198.16 g,and the content of volatiles is 557.22 ng/g.(2)The content of lactones and C6 compounds in flat peach fruits was significantly higher than round peach.The content of “peach flavor” lactones in flat peach is 699.81 ng/g,which is about 2.62 times of round peach(267.11 ng/g);the content of “green flavor” C6 compounds in flat fruit is 1546.52 ng/g.It is about 2.89 times of round peach(535.41 ng/g).(3)Using partial least square discriminant analysis(PLS-DA)to analyze volatiles,found that the variable importance projection(VIP)value is dihydro-β-ionone,indicating that the substance distinguishes the aroma of different color of fleshed in peach.The content of dihydro-β-ionone in white fleshed peach fruits is the highest,followed by red fleshed peaches,and yellow fleshed peaches is the lowest.(4)Comparing the volatile of soft melting flesh,hard melting flesh and non-melting flesh peach fruits,it is found that the content of volatiles such as lactones,C6 compounds and C13 norisoprenoids in soft melting peach fruits is significantly higher than other texture types.In general,soft melting peach fruits have the highest volatiles,hard melting fruit are in the middle,and non-melting flesh peach are the lowest.(5)The content of volatiles are differences in different mature time.Fruits harvested in August have the significantly lower content of lactones and esters than that fruits harvested in June.3.The candidate genes for volatiles metabolism in peach fruit were selected.Based on the correlation analysis between volatiles and gene expression,the candidate genes related to volatile metabolism is carried out.Research have found that the C6 compounds in the fatty acid metabolism pathway is significantly positively correlated with the expression of LOX family genes PpLOX1 and alcohol dehydrogenase family genes PpADH3.The content of γ-Decelactone derived from fatty acid pathway was significantly positively correlated with the expression of PpAAT1,a member of the alcohol acyltransferase family(R=0.65,p<0.05).For the volatiles of terpenoid pathway,the content of terpenes is positively correlated with the expression of PpTPS1,a member of the terpene synthase family.The acquisition of candidate genes provides a basis for the functional identification of the candidate genes and the research on the regulation of volatiles.