The combined application of Debaryomyces hansenii and Bacillus atrophaeus inhibits disease development and enhances postharvest quality in litchi fruit by activating flavonoid metabolism

Abstract

Our previous study demonstrated that the postharvest application of Debaryomyces hansenii (Y-1) and Bacillus atrophaeus (TE-7) significantly reduced decay in litchi fruit, however, the molecular mechanism was not elucidated. Results of the present study indicated that a combined treatment (Y-TE) using both antagonistic strains significantly suppresses an increase in the disease index and inhibits a reduction in the antioxidant properties of litchi fruit during storage at 25 °C. Transcriptomic analysis revealed that genes enriched in phenylpropanoid biosynthesis, flavonoid biosynthesis and plant-pathogen interaction pathways were involved in the response to theY-TE treatment. RT-qPCR analysis indicated that LcMYB102, LcMYB73, and LcMYB33 transcription factors (TFs), and flavonoid synthesis genes, including LcANS and LcF3H, were significantly up-regulated in litchi fruit by the Y-TE treatment after two days of storage. Moreover, an analysis of the metabolome identified eight differentially expressed metabolites associated with flavonoid synthesis, especially formononetin. Furthermore, the regulation of the major pathway and network for flavonoid biosynthesis in litchi fruit by Y-TE was also observed. In summary, our results indicate that the combined application of Y-1 and TE-7 promotes the accumulation of flavonoids in litchi fruit that enhance disease resistance and contributes to the maintenance of quality during storage. The use of these microbial antagonists represents a potential biological approach for the preservation of litchi fruit.