New observations in the spores and hyphae of Colletotrichum siamense exposed to nanochitosan particles.

Colletotrichum siamense is a complex phytopathogen within the Colletotrichum gloeosporioides species, responsible for anthracnose disease in horticultural crops, leading to significant economic losses. Synthetic fungicides are frequently used for control; however, their overuse has resulted in fungal resistance and environmental contamination due to residues accumulation, underscoring the necessity for safer and more effective alternatives. Chitosan nanoparticles provide a feasible alternative with notable antifungal activity against various phytopathogenic fungi. Nonetheless, despite their efficacy against numerous fungi, certain species within the C. gloeosporioides complex have demonstrated reduced susceptibility to the biopolymer, suggesting potential adaptation mechanisms to chitosan nanoparticles. This study assessed the in vitro antifungal efficacy of chitosan nanoparticles against C. siamense. The findings indicated that the biopolymer suppressed mycelial growth by 21.73%. The germination of the spores was delayed by 2 h, accompanied by a decrease in germinative tube length relative to the control group. Nevertheless, an acceleration in growth was observed, resulting in 100% of the spores germinating concurrently with the control group. Furthermore, it was noted that the integrity of both the plasmatic membrane and the cell wall was compromised by the nanochitosan. These findings facilitate the investigation of potential adaptive or defensive mechanisms that C. siamense may employ in response to nanochitosan, offering novel insights for disease management.