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Chitosan (CS), derived from the partial deacetylation and hydrolysis of chitin, varies in the degree of deacetylation, molecular weight, and origin, influencing its biological effects, including antifungal properties. In plants, CS triggers immune responses and stimulates biomass growth. Previously, we found that the antifungal activity of CS was strongly dependent on its physicochemical properties. This study revealed that the chitosan batch CS₁0 with the strongest antifungal activity also effectively activated plant immune responses and promoted biomass growth. Barley treated with CS₁0 exhibited systemic acquired resistance (SAR), characterized by micronecrotic reactions upon Puccinia hordei (Ph) inoculation and reduced symptoms following Fusarium graminearum (Fg) infection, representing biotrophic and necrotrophic pathogens, respectively. CS₁0 treatment (concentration 200 ppm) also enhanced plant biomass growth (by 11% to 15%) and promoted the accumulation of salicylic acid (SA), a hormone that regulates both plant immune responses and growth. Low levels of exogenous SA applied to plants mirrored the stimulation observed with CS₁0 treatment, suggesting SA as a key regulator of CS₁0-induced responses. Transcriptomic analysis identified SA-regulated genes as drivers of enhanced immunity and biomass stimulation. Thus, CS₁0 not only fortifies plant defenses against pathogens like Ph and Fg but also boosts growth through SA-dependent pathways.
Poznanski et al. (Tue,) studied this question.