Study On The Quality Difference Of Peach Fruits In Different Tree Canopy Positions During Fruit Development Process And Cold Storage

Quality of appearance and flavor is an important aspect in evaluating the commodity value of peach[Prunus persica(L.)Batsch]fruits.In order to investigate the differences in quality formation and variation of peach fruits in different tree canopy positions during the fruit development process and cold storage after harvest.In this study,the mid-ripening cultivar‘Xiahui 6’and the late-ripening cultivar‘Xiahui 8’of peach was used as experimental materials.This study investigated the temperature and light intensity dynamic changes of canopy micro-environment as well as values of color difference of pericarp,contents of pericarp pigments,expression levels of genes related to anthocyanin synthesis in pericarp,fruit weight,fruit firmness,soluble solids content(SSC)in flesh,ratio of sugar and acid(RSA),contents of sugar,sorbitol and organic acid of peach fruits in different canopy positions(upper,outer middle,inner middle and lower canopy)during three typical fruit development stages(stone hardening stage,expanding stage and maturing stage).In addition,we investigated the changes in appearance quality and flavor quality of peach fruits after harvest.We also obtained the variation regulations in the quality of fruits in different canopy positions during fruit development and cold storage after harvest.The main research results are as follows:(1)The first experiment analyzed the micro-environments and pericarp color of fruits in different canopy positions,and it was found that the fruits had the deeper red color of pericarp in the canopy positions with a higher level of temperature and light.Some of the fruits of‘Xiahui 6’peach(fruit in upper canopy)and‘Xiahui 8’peach(fruits in upper,outer middle and inner middle canopy)ripe fruits had deeper red color depending on the values of color difference and pigment contents of pericarp.The expression levels of pericarp anthocyanin(Ant)biosynthetic related genes(UFGT,DFR,LDOX,CHS and F3H)during different fruit development stages revealed that all these five genes in pericarp were involved in Ant biosynthesis.Before color change in pericarp,low light intensity could down-regulate the expression levels of the Ant biosynthetic related genes especially UFGT and F3H genes in ’Xiahui 6’ peach,as well as UFGT,DFR and CHS genes in ’Xiahui 8’peach;as compared to the strong light environment,the expression levels of the related genes as mentioned above relatively increased under the weak light environment during fruit maturing stage.(2)The second experiment found that the micro-environments of the upper and outer middle canopy of two cultivars had higher temperature and light levels during fruit development process.During fruit maturing stage,the micro-environment of inner middle canopy of ’Xiahui 8’ peach tree also had a relatively higher temperature and light levels.The light level in lower canopy of two cultivars was always relatively weaker during the experiment.The formation of flavor quality of fruits differed significantly depending on different canopy positions.Relatively higher levels of temperature and light improved the fruit weight,SSC,total sugar content and RSA in flesh during fruit maturing stage,and decreased the total acid content at the same time.The difference of weight of fruits in different canopy positions appeared from fruit expanding stage,while difference of contents of sugar,sorbitol and organic acid in flesh appeared from fruit stone hardening stage,and difference of SSC appeared just during fruit maturing stage.The fruit firmness had no significant difference among different canopy positions of‘Xiahui 6’peach,while the firmness of ’Xiahui 8’ peach fruit in lower canopy was significantly higher than the other fruits from fruit expanding stage.(3)In the third experiment,the red color of pericarp of fruits in all canopy positions increased to some extent of two cultivars during cold storage,but the changing regulations differed significantly among different canopy positions.The red color of pericarp increased of the upper and outer middle canopy fruits of ’Xiahui 6’ peach during the first three days of storage,and it gradually became lighter from the 3rd day after storage,while inner middle canopy and lower canopy fruits faded during the first three days,and then the red color of pericarp became darker.The red color of pericarp of ’Xiahui 8’ peach fruits in all the four canopy positions increased at the beginning of cold storage,and then began to fade.Among them,the lower canopy fruits began to lose red color of pericarp from the 5th day after storage,while the fruits in the other three canopy positions began to fade from the 15th day.The expression levels of UFGT,DFR,LDOX,CHS genes(in pericarp of the lower canopy fruit of ’Xiahui 6’ peach)and UFGT gene(in pericarp of the inner middle fruit of ’Xiahui 6’peach)up-regulated during the final storage phase,and the content of Ant in corresponding pericarp increased at the same time.The results above showed that the harvesting appearance quality of the upper and outer middle canopy fruits of mid-ripening cultivar’Xiahui 6’ peach was better.Despite a certain degree of discoloration,it could still remain an ideal appearance.The appearance quality of lower canopy fruits of late-ripening cultivar’Xiahui 8’ peach at harvest was relatively poor,and the extent of its discoloration was greater,while the appearance of fruits in the other three canopy positions could remain relatively better.(4)In the fourth experiment,the fruit firmness of two cultivars in all the four canopy positions decreased slowly at first and then rapidly during cold storage,among which the softening degree of upper and outer middle canopy fruits was the highest,followed by the inner middle canopy fruit,and the softening degree of lower canopy fruits was the lowest.The variation in trend of fruit SSC of two cultivars was mainly the same as that of total sugar content and RSA in flesh.The SSC of upper canopy fruit of ’Xiahui 6’ peach remained stable,while that of outer middle,inner middle and lower canopy fruits decreased during cold storage.The SSC of lower canopy fruit of ’Xiahui 8’ peach increased rapidly during storage,while that of the fruits in the other three canopy positions decreased.The change in trends of the contents of sugar,sorbitol and organic acid in flesh varied not only among varieties,but also among different canopy positions during storage.The contents of sucrose and total sugar in flesh of ’Xiahui 6’ peach(fruit in lower canopy)and ’Xiahui 8’peach(fruit in upper canopy)decreased significantly.The contents of quinic acid,malic acid and total acid in flesh of the upper canopy fruits of the two cultivars increased significantly.The results above showed that better harvesting quality(mid-ripening cultivar’Xiahui 6’ peach:fruits in upper and outer middle canopy;late-ripening cultivar ’Xiahui 8’peach:fruits in upper,outer middle and inner middle canopy)was beneficial to the relatively better overall quality of fruits during cold storage.’Xiahui 6’ and ’Xiahui 8’peach fruits softened rapidly after the 6th day and 10th day of the storage period,respectively.The softening degree during storage of the fruit with better overall quality at harvest was higher.