Effect Of Nitrous Oxide Fumigation On Postharvest Quality And Black Spot Disease Resistance Of Korla Fragrant Pear

Korla Fragrant Pear is one of the characteristic fruits of Xinjiang,loved by the majority of consumers,but Korla Fragrant Pear fruit is easy to quality deterioration and a variety of diseases occur in the postharvest sales,transportation,storage process due to the temperature and gas and other conditions are unsuitable,seriously affect Korla fragrant pear edible quality and commercial value.Black spot disease caused by Alternaria alternata is the most important fungal disease of Korla fragrant pear after harvest.Nitric oxide（NO）is an endogenous signaling molecule,and can maintain fruit quality and increase resistance to pathogenic fungal infestation on postharvest treatment.In this work,the effect of NO fumigation on postharvest damage control of Korla fragrant pear inoculated with Alternaria alternata and postharvest quality changes in cold storage were investigated.we explored the change pattern of wax fraction and sugar content of fruit epidermis combined with the transcriptome data analysis,and the mechanism of NO fumigation on postharvest quality and disease of Korla fragrant pear was clarified,which provided a theoretical basis for the application of NO in postharvest storage and preservation of fruits and vegetables.The main research results of this work are as follows:（1）Fumigation with exogenous NO fumigation(20μL·L^-1)improved the low-temperature storage quality of Korla fragrant pear.The results demonstrated that,similar to 1-methylcyclopropene（1-MCP）treatment,NO fumigation maintained higher fruit hardness,increased soluble solids（SSC）,titratable acid（TAC）and chlorophyll content,maintained higher color angle h*and lower color difference a*values in the peel,and decreased respiration intensity and ethylene release rate.The respiratory intensity and ethylene release rate of Korla fragrant pear were reduced,and the peroxidase（POD）and phenylalanine aminolase（PAL）enzyme activities as well as glutathione（GSH）and flavonoid contents of Korla fragrant pear were increased,thus delaying the deterioration of Korla fragrant pear fruit quality.Meanwhile,there was no significant difference between NO fumigation and 1-MCP treatment in the main quality,physiological and color indexes of Korla fragrant pear fruits.Therefore,NO fumigation can be an effective way to extend the postharvest shelf life of Korla fragrant pear.（2）NO fumigation treatment can promote Korla fragrant pear epidermal wax synthesis and sucrose decomposition.NO fumigation treatment induced the synthesis of wax and the accumulation of glucose and fructose in the cuticle of postharvest Korla fragrant pear and the breakdown of sucrose and sorbitol.NO treatment significantly increased the total wax content of the epidermis compared with the control.In terms of wax fractions,NO treatment maintained higher alkane and aldehyde contents and lower fatty acid contents compared with the control.NO promoted peel glucose and fructose accumulation and acid convertase（AI）,neutral convertase（NI）,sucrose synthase-catabolic direction（SS-c）,and phosphate synthase（SPS）activities,while inhibiting sucrose and sorbitol catabolism and sucrose synthase-synthetase direction（SS-s）activity.These indicated that NO fumigation could delay the degradation of fruit chlorophyll by inducing epidermal wax synthesis and sucrose catabolism in Korla fragrant pear,and protect Korla fragrant pear fruit from a variety of pathogenic fungi and improve the disease resistance of fruit.（3）Exogenous NO(60μL·L^-1)fumigation treatment improved the resistance of Korla fragrant pear to black spot disease.Within 15 d of storage at room temperature,NO fumigation reduced the black spot damage caused by Alternaria alternata and activated the activities of resistant enzymes,such as peroxidase（POD）,phenylalanine aminolase（PAL）,β-1,3-glucanase（GLU）and chitinase（CHT）,in the infested fruits.With the development of Alternaria alternata infestation process,the spot diameter and spot area of Korla fragrant pear fruits after NO fumigation treatment were significantly lower than those of the control and1-MCP treatment groups,while NO treatment also promoted the accumulation of antioxidant substances such as total phenols and flavonoids,in addition to significantly increasing the activities of the above-mentioned resistant enzymes.This indicates that NO fumigation treatment can delay the process of black spot disease development in Korla fragrant pear fruits,enhance the antioxidant activity of Korla fragrant pear fruits,and improve the resistance of fruits to black spot disease.（4）The effect of NO treatment to Korla fragrant pear on postharvest quality and disease resistance at the molecular level by transcriptome analysis.The analysis showed that NO treatment down-regulated the expression of ethanol dehydrogenase（ADH）,pyruvate kinase（PK）,propanose phosphate isomerase（TPI）and fructose-1,6-bisphosphate aldolase（FBA）,and reduced the consumption of glucose and fructose in Korla fragrant pear during cold storage.NO also improved the resistance to black spot in Korla fragrant pear fruit,mainly by promoting the up-regulated expression of ABA1,phos32,Rboh and AP,which may play an important role in the ABA signaling pathway.These results provide a theoretical basis for the application of NO in postharvest storage and preservation of fruits.