In vitro anti-fungal mechanism of azelaic acid against Botrytis cinerea and its efficacy in controlling gray mold on blueberry fruit

Botrytis cinerea is the causal agent of gray mold in blueberry fruit. This study evaluated the anti-fungal efficacy of azelaic acid (AzA) against B. cinerea both on blueberry fruit and in vitro , along with the possible mechanisms underlying its action. The in vitro results showed that AzA suppressed conidial germination, mycelial growth, and cell viability of B. cinerea . Furthermore, AzA-treated hyphae of B. cinerea exhibited obvious morphological abnormalities including wrinkling, shrinkage, twisting, and even structural breakage. AzA treatment induced intracellular accumulation of malondialdehyde and hydrogen peroxide. It up-regulated superoxide dismutase activity, but inhibited the activities of glutathione reductase, ascorbate peroxidase, and catalase. Meanwhile, it decreased ascorbic acid content and increased dehydroascorbic acid content. Additionally, AzA treatment decreased the relative electrical conductivity of the cell membrane, which in turn induced an increased release of soluble sugars, nucleic acids, and soluble proteins. Furthermore, AzA treatment significantly reduced ergosterol content via the down-regulation of ERG1 and ERG4 . AzA also down-regulated the transcription levels of chitin synthase 2, uridine diphosphate N-acetylglucosamine pyrophosphorylase, and phosphoacetylglucosamine mutase which are involved in the chitin biosynthesis pathway. In vivo results demonstrated that AzA treatment decreased the incidence of natural decay and non-wound inoculation, and also suppressed the weight loss of blueberry fruit. It decelerated the decline in L* value, the rise in a* and b* values, and the reduction of total color difference. Overall, these findings indicate that AzA directly inhibits pathogen growth through disrupting the hyphal morphology, compromising the integrity of the fungal cell membrane and cell wall, and inducing the accumulation of reactive oxygen species in B. cinerea . Furthermore, AzA treatment can induce disease resistance against gray mold, while alleviating postharvest fruit weight loss and color deterioration.