Combined effect of Debaryomyces hansenii and Bacillus atrophaeus on the physicochemical attributes, defense-related enzyme activity, and transcriptomic profile of stored litchi fruit

Postharvest disease and peel browning are critical problems in the storage and transportation of litchi fruit. Our previous studies demonstrated that either Debaryomyces hansenii (Y-1) or Bacillus atrophaeus (TE-7) used individually significantly reduced postharvest diseases in mango fruit. The combined postharvest use of Y-1 and TE-7 on litchi fruit (Litchi chinensis), however, has not been investigated. In the present study, the effect of the combined use of Y-1 and TE-7 on the disease index, physicochemical attributes, defense-related enzyme activity, and the transcriptomic profile of litchi fruit stored at 25 ℃ were investigated. Results demonstrated that the combined use of Y-1 and TE-7 (Y-TE) lowered the browning index (BI) and disease index (DI), inhibited weight loss (WL), reduced electrolyte leakage (EL) and the level of malondialdehyde (MDA) in stored litchi fruit. Y-TE-treated fruit maintained a significantly higher level of total soluble solids (TSS), titratable acidity (TA), and vitamin C (Vc), compared to untreated, control fruit, and also enhanced peroxidase (POD) and superoxide dismutase (SOD) activity. In addition, RNA-seq analysis of the transcriptome of treated and untreated fruit revealed that the Y-TE treatment modulated several metabolic pathways, including those involved in plant-hormone signal transduction and plant-pathogen interaction. RT-qPCR analysis indicated that the expression level of LcAUX28, LcAUX1, LcARF1, LcRD19A, and LcWRKY1 were significantly up-regulated in stored litchi fruit by the Y-TE treatment. Collectively, these findings provide a greater understanding of how Y-TE prevents disease and maintains the quality of stored litchi fruit. The combined use of these biocontrol agents represents a new strategy for managing postharvest diseases and preserving the postharvest quality of litchi fruit during storage and transportation.