Low Molecular Weight and High Deacetylation Degree Chitosan Batch Alleviates Pathogenesis, Toxin Accumulation, and Gene Regulation in Barley Leaf Pathosystem.

is a cosmopolitan fungal pathogen that destroys cereal production, in terms of loss of yield and grain contamination with mycotoxins, worldwide. Chitosan is a natural biopolymer abundant in the environment with proven antifungal properties that also acts as a plant immunity elicitor. Despite a number of articles, there is a lack of systematic comparison of antifungal activity of diverse batches of chitosan. The current study aimed to test the inhibitory effects of a collection of diverse chitosan samples on the growth and production of toxins, validated by changes in the transcriptome. Experiments included testing antifungal activity of different chitosan samples, the application of the best performing one in vitro to investigate the impact on growth, followed by analyzing its effect on toxins accumulation, and transcriptomics in the barley leaf pathosystem. Confirmatory antifungal assays revealed that CS_10, a specific batch of chitosan, retarded growth with an application concentration of 200 ppm, significantly reducing toxin synthesis and disease symptoms in -inoculated barley leaves. RNA-Seq analysis of in barley leaf pathosystem exposed to CS_10 showed a list of differentially expressed genes involved in redox balance, cell respiration, nutrient transport, cell wall degradation enzymes, ergosterol biosynthesis, and trichothecenes production. The genes functioning in these essential pathways are discussed and assigned as critical checkpoints to control infections. The results suggest some important molecular targets in that may be suitable in gene-specific targeting or transgene-free methods, such as spray-induced gene silencing during host-pathogen interactions.