Biofilm formation and response in Exserohilum turcicum

Bacteria are well known and studied for biofilm formation in varying environments. There are however limited studies that have characterised biofilm formation in plant pathogenic fungi. The aim of this study was to assess the biofilm-forming capacity of Exserohilum turcicum , the causal pathogen of Norther leaf blight, under varying environmental conditions, including growth media, temperature, and pH. Biofilm traits namely, metabolic activity, biomass, and extracellular matrix (ECM) production, were analysed on 16 strains under various pH and temperature conditions at two-time points (3 and 7 days). All strains studied formed self-produced gelatinous matrix at an optimum temperature of 25 °C and a pH of 10 at both time points. To further assess the capacity of E. turcicum to form biofilms, two (best and least) biofilm-forming strains among the 16 were subjected to heat treatment at 45 °C and analyzed using scanning electron microscopy (SEM), confocal laser microscopy (CLSM), transmission electron microscopy (TEM). Both strains exhibited increased amounts of ECM when heat-treated compared to the non-heat-treated biofilm. Additionally, the hyphal cell wall thickened under heat treatments. The ECM, being a hallmark of biofilm formation, is often produced by microbial biofilms in response to stressful environments. Therefore, our findings demonstrated that E. turcicum produces biofilms as a survival mechanism, particularly under specific environmental conditions, which supports its persistence and survival in the field.