The Mechanism By Which The Nitrification Inhibitor Nitrapyrin Affects The Fruit Quality Of Korla Fragrant Pear(Pyrus Bretschneideri Rehd.)

[Objective]This study aimed to explore the effects of nitrogen forms on Korla fragrant pear fruit dropping calyx rate and quality and the mechanism of nitrification inhibitor on fruit quality.[Methods ]In this experiment,The Korla fragrant pear trees were thirty years old.Nitrapyrin was applied with urea application amount of 0.3% to soil before flowering.Without adding nitrapyrin as control.In the control group and the treatment group,each of the five trees were selected as five repeats.Soil NH4-N and NO3-N content were measured before irrigation and three days after irrigation.At the early flowering stage and 15 days after flowering,leaves were collected for detected of NH4-N,NO3-N and free amino acid contents detection.At the same time,young fruit at the early flowering stage and 15 days after flowering were collected.Leaves and fruits were frozen in liquid nitrogen for IAA,ABA,ZT and GA3 contents detection.Through High sequencing technology to screening differently expressed genes related to hormone synthesis in 15 days after flowering.The percentage of dropped calyxes was determined 60 days after flowering.Fruit external quality and intrinsic quality were analyzed after fruit ripening.The external quality include:fruit average weight,fruit firmness,fruit shape index.Pear fruit internal quality including:fruit total soluble solids content,total acid content,stone cell content and vitamin C content.[Results](1)Before applying nitrification inhibitor,there was no significant difference between control and treatment in soil NH4-N and NO3-N content.The soil NH4-N content was significantly higher in the nitrification inhibitor treatment than that in the control.The soil NO3-N content were significantly lower in the nitrification inhibitor treatment than that in the control.(2)During the early flowering period,The content of NH4-N,NO3-N and free amino acid had no significantly difference in the leaves of between treatment and control group.At 15 days after flowering,the content of NH4-N and free amino acid had not significantly difference between treatment and control.However,the content of NO3-N significantly lower in the nitrification inhibitor treatment than in the control.(3)Sixty days after flowering,more than 91% of the calyxes were dropped in the nitrapyrin treatment and was significantly higher than that in the control.Fruit average weight and fruit shape index were significantly higher than that of control group.Average fruit hardness was significantly lower than that of control group.Fruit total soluble solid content and total acid content were not significantly different between treatment and control.Fruit vitamin C content were significantly increased and stone cell content was significantly decreased in the treatment group than control.(4)During the early flowering period and 15 days after flowering.The IAA and ZT contents of young pear fruit were significantly lower than the control group;but the ABA content was significantly higher than in the control.There was no significantly difference in GA3 content between control and treatment.(5)Through digital gene expression were analysed for pear young fruit by RNA-Seq.Thedifferent expression genes were screened out of those compared sequences.Two genes related to abscisic acid and one gene related to indole acetic acid synthesis were obtained.[Conclusion]Nitrification inhibitors can reduce the content of nitrate in the soil and result in the nitrogen content reducing in leaves of pear.Low concentration of nitrate nitrogen may affect the endogenous hormones of Korla fragrant pear fruit in the expression of related genes.Therefore,the synthesis and metabolism of endogenous hormones in Korla fragrant pear were affected.As a result,pear calyx rate and fruit quality were improved.