The Effects Of Nitric Oxide And Chlorine Dioxide On Postharvest Disease And Pesticide Residues Of Hami Melon And Table Grape

Xinjiang,one of the major fruit production region,has become the largest Hami melon and grape planting area in China.Due to the disease infection during the transportation,sales and storage,the postharvest losses is up to 20-30%,which directly affects the quality and value of Hami melon and grapes.This has become a bottle neck that restricts the development of agricultural products industry in Xinjiang.On the other hand,with the increasing demands of consumers for safe and high-quality fruits,reducing pesticide residues in fruits and vegetables is also one of the problems that need to be solved urgently.Therefore,it is necessary to find an effective postharvest technology to improve the pathogen resistance,reduce the diseases incidence and degrade the pre-harvest pesticide residue on the Hami melon and grapes.In this paper,the main mechanism of nitric oxide?NO?and chlorine dioxide?ClO₂?in enhancing the postharvest resistance of Hami melon was studied.Through the results of transcriptome analysis,the effect of NO treatment on the hormonal signal transduction during the pathogen infection of Hami melon was thoroughly investigated.The effects of ClO₂ on the quality of grapes and degradation of pesticides residue were also studied.The possible mechanism of pesticide degradation by ClO₂ was analyzed.These will provide a theoretical basis for the application of NO and Cl O₂ in vegetables and fruits post-harvest storage and preservation.The main contents and results of this paper were as follows:?1?The inoculated Hami melons were treated with NO(100?L L^-1)in different order of fumigation.During storage time,the incidence and disease index of Hami melon after NO treatment were significantly lower than the control.Under the infection of T.roseum,NO treatment inhibited the expansion of lesion diameter,retarded the increase of cell membrane permeability and maintained the firmness,soluble solids?TSS?,titratable acid?TA?and pH value as well.Regardless of the NO fumigation treatment carried out before or after inoculation,it can increase the accumulation of ascorbic acid?As A?,improve the activities of ascorbate peroxidase?APX?,peroxidase?POD?and phenylalanine ammonia-lyase?PAL?.NO treatment inhibited the activity of polyphenol oxidase?PPO?and induced the accumulation of defense substances such as lignin,total phenols and flavonoids.The results showed that NO,as a signal molecule,played an important part in the senescence delay and the enhancement of antioxidant activity on Hami melon.The ability to resist the pathogen infection was also strengthened by NO.The inhibitory effect of NO on the pathogenic bacteria was not significant,indicating that NO mainly improved disease resistance of the fruit by inducing rather than by sterilizing.?2?Through the screening and analysis of transcriptome differential gene expression,it was clarified that fruit plant hormonal signal transduction pathway mainly participated in the response of Hami melon fruit resistances.The analysis showed that with the increase of infection time,the related genes in the signal transduction pathways of JA,SA,ET,CTK,GA,and ABA were all up-regulated.While in the CTK signal transduction pathway,in addition to AHP,the remaining genes was also up-regulated.This shows that during the infestation of A.alternata with Hami melon,the co-action of these hormones affected the disease resistance of Hami melon.?3?NO treatment delayed the decrease the firmness and inhibited the increase of lesion depth of infected Hami melons.The endogenous hormone SA content was increased significantly,but the JA content was inhibited simultaneously by NO treatment.Through the analysis to relative expression levels of the related genes in SA and JA signal transduction pathways,it was found that the transmission of SA signals was promoted but JA signals was suppressed by NO,which leading to the quick triggering of the disease resistance response.?4?The ethylene synthesis and signal transduction pathway were affected by NO on enhance the resistance of Hami melon to A.alternata infection.NO decreased the ethylene production and delayed the peak of ethylene and ACC content.The ACS activity was decreased and retarded the ACO activity.Through regulating the ethylene-related gene expression,NO inhibited the synthesis of ethylene in infected Hami melon.This study preliminarily considered that in the ethylene signal transduction pathway,NO possibly regulated the CTR1,EIN2,EIN3 and EBF1 and delayed the transduction of ethylene signal leading to the improvement of the disease resistance.?5?NO treatment increased the content of IAA yet inhibited the content increase of ZR,GA and ABA.The disease resistance of Hami melon was improved by regulating the above four hormone signal transduction pathways.Through analyzing to the expression of related genes,it was found that only the transduction of IAA signal was induced by NO,and the other three hormone signals were suppressed in the signal transmission to some degrees.The ZR,GA and ABA signals were inhibited by AHPs and A-ARR;DELLAs;and PP2Cs,respectively.?6?To study the role of ClO₂ in inhibition of postharvest diseases,the effects of four different Cl O₂ treatments on the control of postharvest disease in Hami melon were compared.The natural disease incidence and disease index were decreased by Cl O₂treatment.The lesion diameter on the inoculated Hami melons was reduced.Cl O₂treatment maintained the firmness and pH,decreased the content of TSS,TA and AsA as well,which improved the postharvest quality of melon.However,ClO₂ treatment could not induce the activities of APX,POD and PAL and had no significant effect on the accumulation of total phenol and lignin.Comparing the different way of Cl O₂ treatment,it was found that the induction effect of ClO₂ on disease-associated enzymes was not obvious.This indicated that the increased disease resistance of Hami melon was mainly achieved through the inhibition of pathogenic bacteria by ClO₂ instead of disease-resistance induction.?7?The use of gaseous Cl O₂ as a strong oxidant to degrade the pesticide residues on the table grapes was studied.ClO₂ releasing process in the sealed box was investigated.The grapes were sprayed with three pesticides and fumigated by ClO₂.After 27 d storage in 0°C,the remaining rates of tebuconazole,azoxystrobin,dimethomorph?E?anddimethomorph?Z?on grapes were 65.33,50.71,39.48 and 41.06%by ClO₂-treatment,respectively.The degradation difference showed that the effect of ClO₂ on pesticide residues were dissimilar.The products formed during the ClO₂ treatment of pesticides were analyzed by GC–MS analysis and the possible mechanism of the degradation was proposed.In the meantime,the postharvest quality of table grapes was also evaluated.