Studies On The Regulatory Mechanisms Of Postharvest Biocontrolagents 34-9 And W176 In Response To Environmental Factors And Their Preservation In Citrus

Citrus is particularly susceptible to pythopathogens contamination during storage and marketing.Postharvest diseases lead to considerable losses,which posed a restriction to the development of citrus industry to a certain extent.Pathogens invasion and proliferation often happened at the wounds or injuries of fruit surface.Biological control is considered to be an environment friendly,safe and replaceable strategy for diseases management,and microorganisms are the mainly biocontrol agents.In the present study,higher resolution genome,and detailed gene expression changes of Kloeckera apiculata34-9 under low temperature and co-incubation with Penicillium digitatum treatments were obtained,respectively.Then we performed pilot-scale trials to test fruit preservation of K.apiculata 34-9 on citrus storage in major citrus producing areas.Meanwhile,we detected the possible antimicrobial mechanisms and the preservation on citrus storage of Bacillus sp.w176 against P.digitatum.The major findings were presented below:1.A total of 8.07 Mb sequences of K.apiculata 34-9 genome was anchored onto 7pesudochromosomes,which accounting for about 99.51% of the whole assembled sequences,and 4,014 coding proteins were annotated from the re-assembled genome.2.Approximately 6.33% of the total genes of K.apiculata 34-9 genome with 254 differentially expressed genes(DEGs)were detected after low temperature treatment,of which 184 and 70 genes were upregulated and downregulated,respectively.The expression of gene Kap001595 remained downregulated through the four time-points,indicating that it might be a core gene for negatively response to low temperature stress.The abundance of gene Kap003732 stayed upregulated throughout the treatments,which might be a positively gene for response to low temperature stress.Meiosis activation related gene was observed involved in the regulation.When co-incubation with P.digitatum,a total of 2,364.DEGs of K.apiculata 34-9 was found during the four time-points,which harbored a 58.90 percent of the whole genome.There were 1,247 upregulated and 1,117 downregulated genes,respectively.Biosynthesis of lysine and arginine,and phenylalanine metabolism were the highest enrichment of the cluster and KEGG analyses of the co-DEGs,they might be involved in the positively regulation of K.apiculata 34-9 response to P.digitatum.3.The changes of citrus fruit qualities were obtained with pilot-scale trials in major citrus producing areas.After storage for 3 months,total soluble solids(TSS)of “Newhall”navel orange fruit,Orah fruit,and W.Murcott fruit handled by K.apiculata 34-9displayed significantly upper value than TSS of tap water bathed fruit,and the maximum difference in TSS was close to 1.0.Titratable acid(TA)of “Newhall” navel orange fruit treated with K.apiculata 34-9 was almost the same to that of tap water treated fruit in Ganzhou,Jiangxi Province,and fruit decay incidence(6.32%)was significantly decreased when treated with K.apiculata 34-9.TA of Orah fruit,and W.Murcott fruit handle by K.apiculata 34-9 were a little higher than the fruit treated by tap water in Guilin,Guangxi Province,and the fruit decay rate was no more than 4.33%.Meanwhile,the joint treatment of K.apiculata 34-9 with sodium bicarbonate(1.25 g/L)or sodium carbonate(1.0 g/L)functionally decreased green mold attack(< 5.0%),but it showed ineffectiveness against citrus sour rot.4.A new strain with potent biocontrol activity against citrus green mold was characterized as Bacillus sp.w176.Bacillus sp.w176 could strongly restrain the expansion of P.digitatum and several other pythopathogens.There were more than four different groups of possible antimicrobial peptides in Bacillus sp.w176 PDB culture filtrate,the metabolites showed synergistic effect when co-incubation with P.digitatum.Meanwhile,the culture filtrate was of UV and heat tolerance to some extent.Subcellular complex changed with vacuolation of P.digitatum was also observed when it was incubated with the culture filtrate,and gene expression analysis indicated a change in redox and ribosome biogenesis stress-related genes transcript levels.Additionally,both Bacillus sp.w176 and its culture filtrate could effectively reduce disease incidence and lesion diameter of green mold of citrus by round percentage of 89.3% and 54.46%,separately.Moreover,they could similarly inhibit the expansion of green mold on citrus with similar effect compared to the fungicide prochloraz after three months of storage with morbidity below 2.0%.The completeness of K.apiculata 34-9 genome and the transcriptome data present here might work as valuable molecular properties for further study on yeast genome,biocontrol agents and environmental factors,and other aspects.Moreover,knowledge of pilot-sacle tirals of K.apiculata 34-9 and Bacillus sp.w176 might be essential for providing relevant information of biocontrol agents and postharvest citrus storage and preservation.