Study On Fruit Russet Formation Of ’Cuiguan’ Pear And Its Control Measurement

’Cuiguan’ pear(Pyrus pyrifolia Nakai)is a new variety hybridized from ’Kousui’ x(’Hangqing’ x ’Xinseik’)by Horticulture Institute of Zhejiang Agricultural Sciences.It is precocious with high fruit quality and wide suitability,and cultivated in large scale of China.However,the fruit surface is generally covered by irregular russet due to the genetic backgroud of Japanses brown of ’Kousui’ pear.The characteristic seriously impairs the appearance quality of the fruits.How to modify the appearance quality of ’Cuiguan’ pear is a serious issue for the pear producers and sellers.Up to now,many scholars have engaged in studying pear skin russet formation,however,no certain conclusion has been obtained even in the composition of the pear russet.Some of learners suggest that pear russet is because of a layer of suberinsuberinite,while the others consider that the fruit russet is closely related to lignin.Some of learners proposed to bag ’Cuiguan’ pears to prevent fruit russet formation,however,the effect in russet prevention is negligible,and the inner favor quality of the fruits become impaired.Therefore,the mechanism for fruit russet formation and how to prevent it formation need further study.In this work,we used ’Cuiguan’ pear fruits as the experimental material to observe the morphological structure and occurrence of russet on the surface of the pear fruits by means of optical microscope,stereo microscope,fluorescence microscope and transmission electron microscope during fruit development.And then,spraying gibberellin and chlorogenic acid in the critical period of the formation of fruit russet on the fruit surface to prevent the fruit russet formation.Finally,the growth and fruit characteristics of the trees sprayed with gibberellin and chlorogenic acid were investigated to understand if any negative effects on flower bud iniation or shoot growth by GA4 + 7 or CA,which should be prevented before the technique was popularized.The main results are as follows:1.We use ’Cuiguan’ as experimental material in the process of growth.The morphological structure and material filling of the internal cells of rust on the surface of the pear fruits were studied by means of optical microscopy,stereo microscopy and fluorescence microscopy.The results showed that ’Cuiguan’ pear rust is mainly broken corneal membrane,lignified thickening of the epidermis and sub-epidermal cells and fruit points on the more easy to peel off the material.Fruit rust formation is due to epidermis,sub-epidermis and near the epidermal cells can not increase with the increase of the fruit,leaving the cell wall lignification thickening.When this mechanical resistance does not counteract the internal swelling,the cells near the peel rupture.Therefore,how to reduce the degree of lignification of epidermal cells,improve cell flexibility and stretch,may be to prevent the occurrence of fruit rust important aspects.In addition,the main time of lentification of epidermal cells was 7-8 weeks after anthesis.This may be the prevention of’Cuiguan’ pear rust formation of the critical period.2.We take ’Cuiguan’ pear as experimental material in the growing period.At 7 weeks and 8 weeks after full blooming,100 mg/L chlorogenic acid(CA)and GA4 + 7 solutions were sprayed on the surface of ’Cuiguan’ pear respectively and water was sprayed at the same time as control.Then,the pear peel was used to continuously observe the occurrence of pear russet,analyze the differences of enzyme activity and gene expression related to lignin synthesis.These results showed that the four treatments could inhibit the occurrence of fruit rust in different degree.Among them,the effect of spraying GA4 + 7 at 7 weeks and CA at 8 weeks after full blooming on fruit russet inhibition was the most obvious.Spraying CA and GA4 + 7 at different periods can increase the content of flavonoids and chlorogenic acid,and can also inhibit the synthesis of lignin.Compared with controls,the activity of phenylalanine ammonialyase and cinnamic acid-4-hydroxylase of the treated fruit showed a trend of increase,while the activity of polyphenol oxidase and peroxidase showed the tendency of decrease.In addition,the expression of POD,,CAD and PPO which were involved in lignin synthesis were reduced,and PAL and 4CL which were involved in chlorogenic acid and flavonoids synthesis were raised.Among them,the up-regulation of the relative expression of PAL and 4CL may be useful to the accumulation of flavonoids and chlorogenic acid,and the inhibition of lignin synthesis.Therefore,the exogenous spraying of CA and GA4 + 7 may increase the accumulation of chlorogenic acid and total flavonoids and can inhibit the synthesis of lignin.Then,treatments may improve the flexibility and resistance of epidermal cell so as to prevent the formation of ’Cuiguan’ fruit russet.3.100 mg/L chlorogenic acid(CA)and GA4 + 7 solutions were sprayed on the surface of ’Cuiguan’ pear respectively and water was sprayed as control.’Cuiguan’ pear trees were used to observe the growth and developmental characteristics and determine the internal quality of fruits by different treatments.To make sure whether CA and GA4 + 7 in the prevention of pear russet formation has other adverse physiological effects or not is useful to take measures for the future production in advance.The results were as follows:there are no significant differences in the number of shoots,shoot growth,flower buds and leaf buds between control and treatments.At the same time,the leaf-related traits such as leaf area,leaf thickness and leaf chlorophyll content had no significant differences between control and treatments.However,the contents of soluble solids and soluble sugar treated by exogenous CA and GA4 +-7 were significantly higher than those of control.Exogenous CA up-regulated the content of soluble protein and vitamin C significantly.Therefore,the exogenous CA and GA4 + 7 had no significant effect on the growth of new shoots and differentiation of flower buds of ’Cuiguan’ pear tree,but could obviously improved the intrinsic quality of fruit.To sum up,’Cuiguan’ pear had the characteristics of formed fruit russet because of genetic russet genes of russet-skin pear.However,in the critical period of fruit russet formation,the application of a certain concentration of CA or GA4 + 7 can down regulate the expression of genes,reduce the enzyme activity which is related to lignin synthesis.So that the fruit russet can be effectively reduced，fruit quality inside and outside will be improved and other growth characteristics of pear tree will be not affected.These results of this study provide a new and simple method for the high quality and efficient cultivation technology of the pear.