Potential utility of endophytic Bacillus altitudinis strain P32-3 as a biocontrol agent for the postharvest prevention of sweet potato black rot

Sweet potato black rot is a common postharvest disease caused by the pathogenic fungus Ceratocystis fimbriata. The toxins produced by infected tubers are potentially harmful to humans. Plant endophytic bacteria may serve as biocontrol agents for protecting crops (including vegetables) during postharvest storage without detrimental effects on humans or other animals. In this study, 11 bacterial strains of Bacillus, Priestia, Blautia, Pseudomonas, and Sphingomonas species were isolated from sweet potato storage roots, of which only one strain (P32-3), which was identified as Bacillus altitudinis, strongly inhibited C. fimbriata mycelial growth and spore germination. Furthermore, the volatile organic compounds and cell-free supernatant of strain P32-3 repressed C. fimbriata growth. Additionally, P32-3 treatments significantly decreased the disease spot diameter and depth on harvested sweet potato roots. A total of 981 differentially expressed genes were identified by comparing the transcriptomes of the control and P32-3-treated mycelia. Strain P32-3 significantly altered the expressions of genes related to cell wall integrity, the cell membrane, spore germination, energy metabolism, pathogenicity, and oxidative stress. In addition, RNA-seq results were validated by a quantitative real-time polymerase chain reaction analysis. Our results indicate that B. altitudinis strain P32-3 can inhibit C. fimbriata growth and development and protect postharvest sweet potato storage roots from C. fimbriata infection. The study findings provide the theoretical basis for future investigations on the utility of strain P32-3 for protecting sweet potato against black rot during the postharvest stage.