| Apricot(Prunoideae armeniaca Mill.)belongs to the genus Apricotaceae of the Rosaceae family and is a typical respiratory transition type fruit.The apricot fruit is harvested in a concentrated season,and quality deterioration and fungal diseases are prone to occur after harvest.Among them,black spot disease caused by Alternaria alternata(A.alternata),greatly reduces the storage quality and commercial value of apricot fruits.In this study,’Samaiti’ apricot fruit was used as a test material.24-Epibrassinolide(EBR)combined with calcium treatment and damage inoculation with A.alternata was explored.EBR combined with calcium treatment was applied to postharvest apricot fruits.Control effect of black spot disease and storage quality,and analyze the physiological mechanism of black spot disease control from the perspectives of active oxygen metabolism,phenylpropane metabolism and cell wall metabolism.Simultaneously,transcriptome sequencing was performed to analyze effect on postharvest apricot fruits WRKY effects of gene expression.The aim is to provide theoretical reference for the study of EBR combined with calcium to regulate the disease resistance mechanism of fruits and vegetables.The test results are as follows:(1)The effect of EBR combined with calcium on the control effect and storage quality of apricot fruit black spot was explored.The results found that:3.0 mg/L EBR combined with 2%calcium chloride could effectively inhibit the incidence of apricot fruit inoculation and the increase in lesion diameter;at the same time,it reduced the fruit respiratory intensity and weight loss rate;slowed down decreasing of soluble solids,titratable acid and Vc content;well maintained hardness and color.This shows that EBR combined with calcium treatment can effectively control the occurrence of black spot disease and decline in storage quality of apricot fruits.(2)The effects of EBR combined with calcium treatment on active oxygen metabolism during postharvest storage of apricot fruits were investigated.The results showed that EBR combined with calcium treatment could effectively increase the H2O2 content in the apricot fruit during the early storage period,and significantly increase the superoxide dismutase(SOD),peroxidase(POD)and catalase during the later storage period Catalase(CAT)activity slowed the increase of fruit cell membrane permeability and the accumulation of malondialdehyde(MDA)content.This shows that EBR combined with calcium treatment inhibits the occurrence of black spot disease in apricot fruits and is closely related to regulating its active oxygen metabolism.(3)The effect of EBR combined with calcium treatment on post-harvest phenylpropane metabolism of apricot fruits was studied.It was found that:EBR combined with calcium treatment induced phenylalanine ammonia lyase(PAL),cinnamate-4-hydroxylase(C4H),4-Coumarate:Co A ligase(4CL),chitinase(CHT),andβ-1,3-glucanase(β-1,3-Glu)increased vitality and increased total phenol and flavonoid accumulation during fruit storage.These results indicate that EBR combined with calcium treatment can enhance the resistance of apricot fruits to black spot disease by regulating phenylpropane metabolism and pathogensis-related proteins(PR proteins).(4)The effect of EBR combined with calcium treatment on the cell wall metabolism of apricot fruits was investigated,and the changes in the epidermal structure and pulp tissue of apricot fruits during storage after inoculation with A.alternata were observed by scanning electron microscope.Tests show that EBR combined with calcium treatment can effectively inhibit polygalacturonase(PG),pectin methylesterase(PME),and β-glucosidase(β-Glu)activity increased;slowed down the increase of water-soluble pectin(CSP)and chelate-soluble pectin(CSP)content in fruits,and maintained the relatively stable content of sodium carbonate-soluble pectin(SSP)and cellulose,the process of cell wall metabolism in apricot fruit was slowed down.At the same time,the scanning electron microscopy results showed that EBR combined with calcium treatment can effectively maintain the integrity of the fruit epidermis and stomata structure,and better inhibit the growth of fruit stomata and pulp hyphae.It shows that EBR combined with calcium treatment can slow down the cell wall metabolism process of postharvest apricot fruits,maintain the relative stability of cell wall components and epidermal structure,and enhance the fruit’s defense ability against pathogenic bacteria.(5)Transcriptome sequencing was performed on apricot pulp tissue on days 0,28,and 49 of storage.The results show that EBR combined with calcium treatment can effectively up-regulate the expression of differential genes in plant hormone signal transduction,pentose and glucuronide conversion,and phenylpropanoids(phenols,flavones,lignin substances)biosynthesis;EBR combined with calcium treatment can also induce the expression of resistance-related genes such as WRKY.This shows that EBR combined with calcium can enhance disease resistance of fruits by regulating differential gene expression in apricot fruits.The above results show that:EBR combined with calcium treatment can effectively maintain the postharvest quality of apricot fruits,and improve disease resistance of apricot fruits by regulating active oxygen metabolism,phenylpropane metabolism,cell wall metabolism,and WRKY gene expression. |
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