Biocontrol efficacy and mechanistic insights of Bullera alba against postharvest tomato diseases caused by Alternaria alternata and Botrytis cinerea.

Antagonistic microorganisms have gained increasing attention for the control of postharvest fruit diseases due to their safety, low risk of resistance development, and capacity to activate the fruit's innate defense responses. This study evaluated the biocontrol potential of Bullera alba against major tomato diseases and elucidated its underlying mechanisms. The results indicated that Bullera alba effectively reduced disease incidence and lesion diameter in tomato fruit and significantly inhibited conidial germination and germ tube elongation of Alternaria alternata and Botrytis cinerea. The strain rapidly colonized tomato wounds at both 25 °C and 4 °C. Furthermore, Bullera alba markedly enhanced the activities of POD, PPO, SOD, APX, and PAL, and significantly promoted the accumulation of total phenolics, flavonoids, and lignin. Transcriptomic analysis indicated that Bullera alba treatment significantly upregulated the expression of genes associated with several defense-related pathways in tomato fruit, including plant-pathogen interactions, phenylpropanoid biosynthesis, glutathione metabolism, and MAPK signaling pathways. Overall, these findings suggest that Bullera alba may enhance tomato fruit resistance to two major postharvest diseases by inducing the expression of defense-related genes, increasing defense enzyme activities, and promoting the accumulation of bioactive secondary metabolites.