Gene expression studies of malting induced germination of barley seeds in response to Alternaria alternata infection

Barley infection with Alternaria alternata (A. alternata) can impair malting quality and lead to considerable yield losses. Despite the widespread prevalence and significance of A. alternata as a plant pathogen, the intricacies of its impact on malting barley remain insufficiently explored. This study aims to improve our understanding of how malting barley responds to biotic stress conditions induced by A. alternata infection during the malting process and how this impacts the phenotypic quality characteristics of barley malt. Barley grains artificially infected with A. alternata were malted according to the standardized malting procedure, and samples were taken at 11 time points during the malting process. Gene expression analysis using quantitative real-time PCR demonstrated pathogen-induced alterations in the expression of malting- and stress-related genes, with the strongest differences observed within a short time after infection, during the first wet steeping, and within the first 24 h of the malting process. Standard malt quality parameters showed an impact on the phenotypic quality parameters viscosity (-8.86%), wort color (+ 25.31%), free amino nitrogen (FAN) (+ 11.90%), and β-glucan (-76.32%). A. alternata behaviour during malting was quantified using qPCR, indicating that fungal growth was favored during the aeration and germination phases. Especially in the germination phase, there was a considerable 3.5-fold increase in fungal biomass. These findings contribute to a more comprehensive understanding of A. alternata and its role in malting and emphasizes the importance of disease management and recommendations for processing affected batches to maintain high malt quality.