Effects Of Chemical And Physical Elicitors Treatments On Rhizopus Rot Control In Postharvest Peach Fruit And Possible Mechanisms

Peach(Prunus persica)are deeply loved by customers for their pleasant aroma and appealing taste.Peach mature in hot rainy season and are susceptible to pathogen because of their thin peel and soft flesh.Rhizopus rot caused by Rhizopus stolonifer is one of the most severe diseases in peach fruit.Traditional postharvest preservation methods are low temperature cold storage and modified atmosphere conditioning to postpone fruit ripening and senescence which strongly rely on chemical fungicides to enhance eflfect.However,chenical fingicides induce resistance in pathogen and reduce efficacy with a long-term use.Residue and pollution to environment are more and more conceemed by people.Therefore,exploring healthy and eco-firiendly strategies are of vital important to reduce decay in peach.Methyl jasmonate(MeJA),p-aminobutyric acid(BABA),nitric oxide(NO)which are chemical elicitors and heat treatment which is physical elicitor were found to be effective in plant disease control which are potential alternative strategies to chemical ’fungicides.They have been widely used in decay control of postharvest fruit and vegetables.MeJA3 BABA,NO and heat treatment induce resistance in peach.Priming has been found in Chinese bayberry and grape with MeJA and BABA treatment.While,the mechanisms of induced resistance have not been deeply explored in peach with MeJA,BABA,NO and heat treatment.This study was designed to investigate the effect of these four inducers on Rhizopus rot control and explore the priming phenomenon in peach.RNA-seq and iTRAQ were conducted to identify the key genes that control induction resistance:in order to provide a theoretical basis for inducers application in postharvest peach disease control.The main results are as following:(1)MeJA,BABA,NO and heat treatment significantly reduced disease incidence and lesion diameter of Rhizopus rot in postharvest peach.In vitro,heat treatment inhibited spore germination,germ tube length and mycelia growth of Rhizopus stolonifer.While,similar results were not observed in MeJA,BABA,NO treatment.Four treatments inducedβ-1,3-glucanase(GLU),chitinase(CHI),phenylalanine ammonia-lyase(PAL)activites and arouse the increase of lignin,phenolic and flavonoids content.PpPR-like,PpGNS,PpCHI were enhanced by inducers.The induction model of compounds,enzymes and genes expression showed that MeJA,BABA,NO induced disease resistance in peach by prining and heat treatment induce disease resistance directly.(2)To investigate the effect of priming and directly induced resistance mechanisms in consumption and energy metabolism,peach quality as well as monosaccharide,ATP content and energy metabolism in mitochondrion were measured.The results showed that there was no significant aflfection on peach quality with the four treatnents.MeJA,BABA and NO delayed the decrease of sucrose,fructose and glucose content,while,heat treatment significantly lowered the monosaccharide content.Sorbitol content was induced by the four inducers which indicated that sorbitol is related to disease resistance induction.MeJA,BABA and NO cause less consumption in energy compared to un-treatment group.Heat treatment cause more consumption compared to chemical inducers.These results corroborated that priming induced by MeJA,BABA and NO is more econorrucal to plants than direact induction resistance induced by HT.(3)RNA-seq was conducted to investigate the possible mechanisms in phenylpropanoid biosynthesis and MAPK signaling pathway to provoke priming and direct induction Mrhich was induced by MeJA and heat treatment independently.The results showed that DEGs induced by MeJA in phenylpropanoid biosynthesis verified as priming manner and DEGs induced by heat treatment directly which was similar to the variation of phenolic and lignin content.DEGs varied greatly in MeJA and heat treatment.The results showed that MAPKKKI and WRKY33 induced by heat treatment are responsible to arouse directly induction.MAPK1/2 and MYC2 was induced by MeJA only indicating that these two proteins motivated priming in peach resistance to Rhizopus stolonifer.(4)Based on iTRAQ technology,up-regulation of differential expression proteins induced by BABA were significantly annotation to response to stimulus,multi-organism process,molecular function regulator and cell part.KEGG enrichment of total differential expressed proteins appeals to metabolic pathways,lipid pathways,amino acid metabolism.BABA:induced pathogen-related protein,abscisic-aldehyde oxidase and E3 ubiquitin protein ligase in peach,which indicated that resistance induced by BABA is closely related to abscisic acid signaling and protein modification mediated by E3 ubiquitin protein ligase.