Study On The Biological Control Of Postharvest Disease Of Peaches By Pichia Membranaefaciens Y4 And The Preparation Of The Yeast

Peach(Prunus persica)is an important economic fruit in China.Postharvest peaches are susceptible to pathogens and resulted in serious economic losses.The Rhizopus rot caused by Rhizopus stolonifer is one of the main postharvest diseases of peaches.In this paper,the antagonistic yeast with the ability of controlling Rhizopus rot of peaches were screened and the physiological mechanisms were revealed.The molecular mechanism of induced disease resistance of peaches by this antagonistic yeast were analyzed by transcriptome technology.In addition,the preparation conditions of the liquid and solid preparation of this antagonistic yeast were optimized.The main research results are as follows:(1)Four strains(Y1,Y2,Y3 and Y4)were screened from the samples collected from peach orchards.Among them,Y4 had the significant control efficacy on Rhizopus rot of peaches.(The decay incidence and lesion diameter of peaches treated with Y4 for72 h were 26.23%and 11.60 mm,respectively.While these two indexes were 95.70%and 35.72 mm.The morphological properties and molecular identification indicated that Y4 is Pichia membranaefaciens.Acute toxicity test showed that the yeast was a non-toxic and safety yeast.(2)The in vivo results showed that different concentrations of P.membranaefaciens Y4 could significantly reduce the decay incidence and lesion diameter of peaches caused by Rhizopus rot.Compared with the control,the natural decay incidence of peaches treated with P.membranaefaciens Y4(1×10~8 cells/mL)was reduced by 19.44%,and had no significant adverse effect on its quality.The results about the inhibitory effect of the yeast on the spore germination of R.stolonifer,the growth of this yeast on peaches,four resistance-relating enzyme activities and malondialdehyde(MDA)content in peaches showed that the physiological mechanisms of controlling the Rhizopus rot of peaches by this antagonistic yeast including:(1)directly inhibiting the germination of R.stolonifer spores(the spore germination rate was decreased by 46.82%);(2)competing with pathogens for space and nutrition to inhibit its growth;(3)inducing the activities of resistance-related enzymes such as Polyphenol oxidase(PPO),Peroxidase(POD),Phenylalanine ammonia lyase(PAL)and Catalase(CAT)in peaches,thereby enhancing the resistance of peaches against postharvest pathogens.(3)The molecular mechanisms of induced disease resistance in peaches by P.membranaefaciens Y4 were analyzed by transcriptome technique.The results showed that there were 796 differentially expressed genes(DEGs)in peaches treated with P.membranaefaciens Y4.Among which,391 were up-regulated and 405 were down-regulated.Combining with GO enrichment analysis and KEGG enrichment analysis of the DEGs,the molecular mechanisms of induced disease resistance of peaches by P.membranaefaciens Y4 were revealed as follows:(1)inducing the expression of genes related to synthesis of resistant substances in peaches including terpenoids,flavonoids and lignin,such as GGPS,PAL1,CHS1,PKS5,DFR,ANS,CYP75B2,PNC1 and ROMT,thereby improving the disease resistance of peaches;(2)inducing the expression of some transcription factor genes of peaches in ET,JA and SA synthesis and signal transduction pathways,such as ERF115,MYC4,WRKY18,WRKY53 and WRKY33,so as to activate the expression of downstream defense genes such as the encoding genes of PR-1,PR-3 and PR-10,thereby improving the disease resistance of the peaches;(3)affecting the expression of some important genes in the plant-pathogen interaction pathway,such as the down-regulation of RBOHA,the up-regulation of CML48 and MUK11.19,to decrease the oxidation damage and affect the hypersensitivity reaction,cell wall enhancement and stomatal closure of peaches,thereby enhancing the resistance of peach fruit to pathogens.(4)The preparation conditions of P.membranaefaciens Y4 liquid preparation were optimized by orthogonal test.The results showed that the optimal formulation of the liquid preparation protectant was 5%trehalose,0.12%ascorbic acid and 5%mannitol.The survival rate of the yeast in the prepared liquid preparation stored at 25℃for 15days was 52.30%(32.13%in the control).Stored at 4℃for 90 days,the yeast survival rate in the preparation was 50.98%(10.66%in the control).The spray drying conditions for the solid preparation of P.membranaefaciens Y4 optimized by single factor test were as follows:the ratio of different wall materials(Arabia gum:Trehalose=1:1),the mass concentration of wall material 100 g/L,atomization pressure 200 kPa,inlet temperature 100℃and feed rate 15 mL/min.The survival rates of P.membranaefaciens Y4 in solid preparation stored at 25℃and 4℃for 90 days were 66.97%and 82.91%,respectively.The solid preparation of P.membranaefaciens Y4 could significantly reduce the incidence of Rhizopus rot of peaches(37.04%),slightly higher than that of the fresh yeast(31.48%).