Exploring the biocontrol performance of Bacillus velezensis against postharvest diseases of eggplants and the underlying action mechanisms in soft rot management

Abstract

Postharvest eggplants are highly vulnerable to pathogen invasion, which results in quality deterioration and economic losses. Previous research has shown that Bacillus velezensis significantly reduced the soft rot occurrence of eggplants through producing cyclic lipopeptides and improving reactive oxygen species (ROS) scavenging capability of eggplants. In the present study, the mechanisms involved in soft rot management by B. velezensis were explored in depth, and a broad-spectrum biocontrol efficacy of this antagonistic bacterium against other major postharvest diseases of eggplants was further investigated. The results exhibited that B. velezensis has the ability to inhibit critical postharvest pathogens of eggplants, including Botrytis cinerea and Alternaria alternate. More importantly, this antagonistic bacterium decreased natural decay rate of eggplants from 72.25 % to 31.5 %. It suggested that this antagonist possessed extensive control effectiveness against primary diseases of postharvest eggplants. The effective biofilm formation of B. velezensis facilitated its colonization on fruit, which contributed to the biocontrol of postharvest diseases in eggplants. The exploration based on biochemical and transcriptomic analysis revealed that B. velezensis application resulted in the up-regulation of genes involved in Ca²⁺ signaling, plant hormone signaling, and bacterial AvrRpt2-mediated signaling in eggplants. Further, it triggered the expression of important genes involved in ROS scavenging and other defense responses, and boosted the activities of key defensive enzymes. Besides, B. velezensis application activated the genes involved in synthesizing resistance-associated secondary metabolites, such as lignins, flavonoids and anthocyanins, which align with the increased accumulation of these metabolites observed in eggplants. Collectively, the resistance against soft rot was stimulated in eggplants. This study offers valuable insights into the complex mechanisms by which antagonists like B. velezensis control postharvest diseases of eggplants and paves the way for developing strategies to control postharvest diseases in eggplants.