Hormone Changes In Calyx Leaves Of ‘Korla Fragrant Pear’ And Its Effect On Fruit Quality

‘Korla fragrant pear’（Pyrus sinkiangensis Yü）belongs to the Xinjiang pear system of Rosaceae,Pear Subfamily and Pear genus,which is one of the characteristic fruit trees in Xinjiang.‘Korla fragrant pear’is famous at home and abroad because of its appearance,rich aroma and sweet taste.It has become one of the important industries for farmers to improve the quality of life and improve the economic level in Korla area.Sepal persistence is one of the important factors affecting fruit quality,which seriously reduces the economic benefits of fragrant pear and affects the healthy development of fragrant pear industry.At present,the mechanism of sepal abscission is mostly in the abscission zone,and there are few studies on the upper and lower parts of the abscission zone.The fruit quality of‘Korla fragrant pear’mainly focused on the effects of varieties and pollination on fruit quality.There were few comprehensive studies on the internal quality,external quality and aroma of decalyx fruit and persistent calyx fruit under natural conditions.In this study,10-year-old‘Korla fragrant pear’was used as experimental material.By investigating the law of sepal abscission,observing the anatomical structure of abscission zone,and determining the content of phytohormones in abscission zone and corresponding parts,the relationship between sepal abscission characteristics,process and abscission zone formation and phytohormones in different parts was clarified.The effects of sepal abscission on fruit quality were determined by determining the fruit quality of decalyxed and persistent calyxed pears at mature stage.The results were aimed to reveal the regulatory effect of plant hormones on the sepal abscission of‘Korla fragrant pear’,and provide a scientific basis and reference for the selection of high-quality fruit in production.The main research is as follows:（1）Through the investigation on the apparent traits of sepal abscission of‘Korla fragrant pear’,it was found that the second sequence was the earliest abscission(April 20^th),and the fifth sequence was the latest abscission(April 22^th).The first sequence shedding peak was the earliest,and the fifth sequence shedding peak was the latest.The calyx removal rate in the first sequence was the lowest（13.46%）,and that in the fifth sequence was the highest（18.65%）.In summary,the sepal sequence of‘Korla fragrant pear’is proportional to the sepal decaly rate and decaly time.（2）By observing the development process of sepal abscission zone of‘Korla fragrant pear’,it was found that before the abscission zone was formed,there was only a catheter in the abscission zone of decalyx fruit,while there were catheters and allogeneic cells in the corresponding parts of the abscission zone of persistent calyx fruit.Mitochondria in the decalyx zone were distributed around the cell wall,and mitochondria in the corresponding parts of the persistent calyx zone were scattered in the cells.During abscission formation,abscission layer appeared in abscission zone of decalyx fruit,no abscission layer appeared in persistent calyx fruit,but new tissue of sieve tube developed and formed.There were only plastid globules and starch granules in the chloroplast of decalyx fruit abscission zone,while there were two organelles in the chloroplast of the corresponding part of the persistent calyx fruit abscission zone,plastid globules and starch granules,and there was no starch granules in the cell.After the abscission zone formed,protective layer appeared obviously in abscission zone of calyx,and no protective layer appeared in persistent calyx.There were starch granules in the cells and chloroplasts of decalyx fruit abscission zone,and there were no starch granules in the internal cells and chloroplasts,but there were a large number of plastid spheres in the chloroplasts,and the cells were accompanied by the generation of Golgi bodies.In summary,there were no ethmoidal and allogeneic tissues in the abscission zone of decalyx fruit.There was no starch precipitation in chloroplasts,and a large number of starch precipitation in cells.The above tissues and organelles were found in the corresponding parts of persistent calyx fruit.（3）Through the determination of plant hormones in different parts of sepal abscission zone of‘Korla fragrant pear’,it was found that before the formation of abscission zone,the content of IAA in abscission zone(0.021 mg·g^-1)was lower than that in corresponding part of persistent calyx fruit(0.029 mg·g^-1),and the content of IAA in upper part of persistent calyx fruit abscission zone(0.019 mg·g^-1)was significantly higher than that in lower part of abscission zone(0.010 mg·g^-1).During the formation period of abscission zone,the contents of abscisic acid（ABA）(3.429 mg·g^-1)and gibberellin（GA₃）(0.030 mg·g^-1)in the abscission zone of decalyx fruit were higher than those in the corresponding parts of persistent calyx fruit(1.772 and 0.018 mg·g^-1).The ABA content in the upper part of abscission zone of decalyx fruit(1.871 mg·g^-1)was significantly higher than that in the lower part of abscission zone(1.588 mg·g^-1).The GA₃ content in the upper part of abscission zone of decalyx fruit(0.014 mg·g^-1)was significantly higher than that in the corresponding parts of persistent calyx fruit(0.002mg·g^-1).Before abscission zone formation,zeatin（ZR）content in abscission zone(0.050 mg·g^-1)was higher than that in persistent calyx(0.045 mg·g^-1),and ZR content in upper abscission zone(0.028 mg·g^-1)was significantly higher than that in lower abscission zone(0.022 mg·g^-1).In summary,IAA and ZR play a major role before abscission formation,the former inhibits abscission in the upper part of abscission zone,the latter promotes abscission in the upper part of abscission zone,ABA and GA₃ play a major role in abscission formation,both promote abscission in the upper part of abscission zone.（4）Through the analysis of the appearance quality of decalyxed fruit and persistent calyxed fruit of‘Korla fragrant pear’,it was found that the longitudinal diameter（59.79 mm）,transverse diameter（55.24 mm）,single fruit weight（100.58 g）and fruit shape index（1.08）of decalyxed fruit were lower than those of persistent calyxed fruit（63.74 mm,58.43 mm,119.23 g,1.09）.Calyx peel is dominated by alcohols,18species,accounting for 52.99%.The calyx-free pulp was mainly composed of alcohols and esters,with 13and 3 species,accounting for 20.85%and 71.91%,respectively.The pericarp and pulp of persistent calyx were dominated by alcohols,with 12 and 10 species,accounting for 85.35%and 86.18%,respectively.In summary,the fruit shape of decalyxed fruit was regular,and the fruit weight was slightly light.The volatile substances in peel and pulp were mainly alcohols.The fruit shape of persistent calyx was patchy,and the fruit weight was slightly heavy.The peel and pulp were also mainly alcohols.（5）Through the analysis of the internal quality of decalyx fruit and persistent calyx fruit of‘Korla fragrant pear’,it was found that the hardness（8.66%）,soluble sugar(20.05 mg·g^-1),reducing sugar(15.50mg·g^-1)and vitamin C(4.90 mg·g^-1)of decalyx fruit flesh were higher than those of persistent calyx fruit flesh.Soluble sugar(17.05 mg·g^-1)and reducing sugar(13.20 mg·g^-1)in peel of decalyx were higher than those in peel of persistent calyx.The contents of fructose(9.17 mg·g^-1),glucose(9.35 mg·g^-1),lactose(0.16mg·g^-1)and succinic acid(16.27 mg·g^-1)in the flesh of decalyxed fruit were higher than those in the flesh of persistent calyxed fruit.The contents of fructose(6.31 mg·g^-1),glucose(9.65 mg·g^-1),tartaric acid(0.02mg·g^-1),lactic acid(1.89 mg·g^-1),and succinic acid(0.24 mg·g^-1)in peel of decalyxed fruit were higher than those in peel of persistent calyxed fruit.In summary,decalyx fruit quality is better than persistent calyx fruit.