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Postharvest anthracnose, caused by the fungus Colletotrichum gloeosporioides, is one of the most important postharvest diseases of mangoes worldwide. Bacillus siamensis (B. siamensis), as a biocontrol bacteria, has significant effects on inhibiting disease and improving the quality of fruits and vegetables. In this study, pre-storage application of B. siamensis significantly induced disease resistance and decreased disease index (DI) of stored mango fruit. To investigate the induction mechanisms of B. siamensis, comparative transcriptome analysis of mango fruit samples during the storage were established. In total, 234,808 unique transcripts were assembled and 56,704 differentially expressed genes (DEGs) were identified by comparative transcriptome analysis. Gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of DEGs showed that most of the DEGs involved in plant-pathogen interaction, plant hormone signal transduction, and biosynthesis of resistant substances were enriched. Fourteen DEGs related to disease-resistance were validated by qRT-PCR, which well corresponded to the FPKM value obtained from the transcriptome data. These results indicate that B. siamensis treatment may act to induce disease resistance of mango fruit by affecting multiple pathways. These findings not only reveal the transcriptional regulatory mechanisms that govern postharvest disease, but also develop a biological strategy to maintain quality of post-harvest mango fruit.

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Objectives The purpose of this study was to evaluate the effect of combined postharvest use of Bacillus siamensis strain and chlorogenic acid on quality mainteance and disease control in wax apple fruit. Materials and Methods Wax apple fruit were treated with Bacillus siamensis strain (N1), chlorogenic acid (CHA) and N1+CHA and preserved at 25℃for 12 days. The appearance and quality parameters were evaluated, along with the disease index (DI), content of total soluble solids (TSS), total acid (TA), vitamin C (Vc), total phenolic, and flavonoids during cold storage. Meanwhile, the activities of β-1,3-glucanase (GLU) , phenylalanine ammonialyase (PAL), polyphenol oxidase (PPO), and peroxidase (POD) were determined. Furthermore, the transcriptome and the expression level of key defense enzyme genes were analyzed by RNA-seq and real-time quantitative reverse transcription PCR (qRT-PCR). Results N1+CHA treatment significantly lowered DI and delayed fruit quality deterioration by slowing TSS and TA loss and enhancing antioxidant capacity, including Vc, total phenolic, and flavonoids content. Meanwhile, the activities of GLU, PAL, PPO and POD were dramatically increased by N1+CHA treatment. Additionally, N1+CHA treatment modulated several metabolic pathways, including those involved in plant-hormone signal transduction and plant-pathogen interaction. The expression level of key defense enzyme genes were significantly up-regulated in stored wax apple fruit by the N1+CHA treatment, which were well coincided with the transcriptome data. Conclusion The combined use of N1+CHA significantly prevent disease and maintain fruit quality of wax apple during storage. These findings indicate that it could serve as a promising biological technique for preserving wax apple fruit.

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